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METALLOGRAPHY

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Originally appearing in Volume V18, Page 215 of the 1911 Encyclopedia Britannica.
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METALLOGRAPHY .—The examination of metals and See also:

alloys by the aid of the See also:microscope has assumed much importance in comparatively See also:recent years, and it might at first be considered to be a natural development of the use of the microscope in determining the constitution of rocks, a study to which the name petrography has been given. It would appear, however, that it is an See also:extension of the study of the structure of meteoric irons. There can be no question that in the See also:main it was originated by Dr H. C. Sorby, who in 1864 gave the See also:British Association an See also:account of his See also:work. Following the work of Sorby came that of See also:Professor A. See also:Mar!ens of See also:Charlottenburg, presenting many features of originality. F. Osmond has obtained results in connexion with See also:iron and See also:steel which are of the highest See also:interest. A See also:list of the more important papers by these and other workers will be found in the appended bibliography. Preparation of the Specimen.—Experience alone can enable the operator to determine what portion of a See also:mass of See also:metal or alloy will afford a trustworthy See also:sample of the whole. In studying a See also:series of binary alloys it has been found advantageous in certain cases to obtain one See also:section which will show in a See also:general way the variation in structure from one end of the series to the other.

This has been effected by pouring the lighter constituent carefully on the See also:

surface of the heavier constituent, and allowing solidification to take See also:place. •A section through the culot so obtained will show a gradation in structure from pure metal on one See also:side to pure metal on the other. A thin slice of metal is usually cut by means of a hack-saw driven by mechanism. The thickness of the piece should not be less than 4 in. and in See also:order that it may be firmly held between the fingers it should not be less than 1 in. square. The preliminary stages of polishing are effected by See also:emery See also:paper placed preferably on wooden disks capable of being revolved at a high See also:rate of See also:speed. The finest grade of emery paper that can be obtained is used towards the end of the operation. Before use the finer papers should be rubbed with a hard steel surface to remove any coarse particles. The completion of the operation of polishing is generally effected on wet See also:cloth or See also:parchment covered with a small amount of carefully washed jeweller's See also:rouge. Various See also:mechanical appliances are employed to minimize the labour and See also:time required for the polishing. These usually consist of a series of interchangeable revolving disks, each of which is covered with emery paper, cloth or parchment, according to the particular See also:stage of polishing for which it is required. In the See also:case of brittle alloys and of alloys having a very soft constituent, which during polishing tends to spread over and obliterate the harder constituents, polishing is in many cases altogether avoided by casting the alloy on the surface of See also:glass or See also:mica. In this way, with a little care, a perfect surface is obtained, and it is only necessary to develop the structure by suitable See also:etching.

In adopting this method, however, instances have occurred in which the removal of the See also:

cast surface has shown a structure differing considerably from the See also:original. Polishing in Bas-See also:Relief.—If the polishing be completed with See also:fine rouge on a See also:sheet of wet parchment, placed upon a comparatively soft bas such as a piece of See also:deal, certain soft constituents of an alloy may often be eroded in such a manner as to leave the hardest portions in relief. For the later stages of polishing H. L. Le Chatelier recommends the use of alumina obtained by the calcination of ammonium See also:alum; and for the final See also:polish of soft metals, See also:chromium See also:oxide. Although in some cases a See also:pattern becomes visible after polishing, yet more frequently a See also:mirror-like surface is produced in which no pattern can be detected, or if there is a pattern it is blurred, as if seen through a See also:veil or mist. This is due to a thin layer of metal which has been dragged, or smeared, uniformly over the whole surface by the See also:friction of the polishing See also:process. Such a surface layer is formed in all cases of polishing, and the See also:peculiar lustre of burnished See also:silver or steel is probably due to this layer. But to the metallographist it is an inconvenience, as it conceals scratches See also:left by imperfect polishing, and also hides the pattern. It is therefore desirable to conduct the polishing so as to make this layer as thin as possible: it is claimed for alumina that it can be so used as to produce a much thinner surface layer than that due to the employment of rouge. The surface layer is very readily removed by appropriate liquid reagents, and, the true surface of the metal having been laid See also:bare, the etching reagent acts differently on the individual substances in the alloy and the pattern can thus be emphasized to any required extent. Osmond divides etching reagents into three classes—acids, See also:halogens and salts.

As regards acids, See also:

water containing from z to ro% of hydrochromic See also:acid is useful. It is made by mixing to grams of See also:potassium bichromate with ro grams of sulphuric acid in roo grams of water. The use of nitric acid requires much experience. It is frequently employed in the examination of steels, See also:Sir W. C. See also:Roberts-See also:Austen preferred a 1% See also:solution in See also:alcohol, but many workers use concentrated acid, and effect the etching by allowing a stream of water to dilute the film of acid left on the surface of the specimen after dipping it. Of the halogens, See also:iodine is the most useful. A solution in alcohol is applied, so that a single drop covers See also:half a square See also:inch of surface. The specimen is then washed with alcohol, and dried with a piece of fine See also:linen or See also:chamois See also:leather. See also:Tincture of iodine also affords a means of identifying See also:lead in certain alloys by the formation of a yellow iodide of lead, while the vapour of iodine has in certain cases been used to tint the constituents. Thin coloured films may often be produced by the oxidation of the specimen when heated in See also:air. This, as a means of developing the structure, in the case of the See also:copper alloys is specially useful.

Tinted crystals may thus be distinguished from the investing layer caused by the presence of a See also:

minute quantity of another constituent. The See also:temper See also:colours produced by See also:heating iron or steel in air are well known. See also:Carbide of iron is less oxidizable than the iron with which it is intimately associated, and it assumes a See also:brown tint, while the iron has reached the See also:blue stage. These coloured films may be fixed by covering with thin films of gelatine. In some cases the alloy may be attacked electrolytically by exposing it for a few minutes to a weak electric current in a See also:bath of very dilute sulphuric acid. Certain organic bodies give very satisfactory results. The See also:Japanese, for instance, produce most remarkable effects by See also:simple reagents of which an infusion of certain forms of grass is a not unimportant constituent. In the case of iron and steel a freshly prepared infusion of See also:liquorice See also:root has been found to be most useful for colouring certain constituents of steel. Osmond, who was the first to use this reagent, insisted that it should be freshly prepared and always used under identical conditions as regards See also:age and concentration. His method of applying it was to rub the specimen on parchment moistened with it, but he has subsequently modified this " polish attack " by substituting a 2% solution of ammonium nitrate for the liquorice infusion. In each case a small quantity of freshly precipitated See also:calcium sulphate is used on the parchment to assist the polishing. Appliances used in Micrography.—The method of using the microscope in connexion with a See also:camera for photographic purposes will now be considered.

Every micrographer has his own views as should be an achromatic one, as See also:

colour effects cause trouble in photographing the See also:objects. For See also:lower See also:powers the Lieberkuhn parabolic illuminator is useful. Certain See also:groups of alloys show better under oblique See also:illumination, which may be effected by the aid of a See also:good condensing See also:lens, the See also:angle of incidence being limited by the distance of the See also:object from the See also:objective in the case of high magnification. As regards objectives, the most useful are the Zeiss 2 mm., 4 mm. and 24 mm.; two other useful objectives for See also:low powers being 35 mm. and 70 mm., both of which are projecting objectives. A projecting See also:eye-piece, prefer-ably of low See also:power, should be employed with all but the two latter objectives. The See also:immersion lens, the Zeiss 2 mm., is used with specially thickened See also:cedar oil, and if the distance from the objective to the See also:plate is 7 feet, magnifications of over 2000 diameters can easily be obtained. As regards sensitized plates, excellent results have been obtained with Lumiere plates sensitive to yellow and See also:green The various brands of " process " plates are very serviceable where the contrasts on the specimen are not See also:great. Some reproductions of photo-micrographs of metals and alloys will be found in the plate accompanying the See also:article ALLOYS. W. C. Roberts-Austen and F. Osmond, " On the Structure of Metals, its Origin and Causes," Phil.

Trans. See also:

Roy. See also:Soc. clxxxvii. 417—4.32; and See also:Bull. de la Soc. d'encouragement pour l'industrie nationale, 5e eerie, i. 1136 (Aoflt 1896) ; G. Charpy, " Micro- Micrographic Apparatus. scopic Study of Me- tallic Alloys," Bull. to the See also:form of an See also:installation to be adopted, and it will therefore I de la sec. d'encouragement pour l'industrie nationale (See also:March, 1897) ; A. be well to give an See also:illustration of a definite apparatus which has Sauveur, Constitution of Steel," Technology Quarterly (See also:June, 1888) ; been found to give satisfactory results. It consists of a micro- See also:scope A with a See also:firm See also:base placed in a See also:horizontal position. The microscope can be connected by a See also:tube; B with the See also:expanded camera CC, at the end of which .is the usual See also:frame to receive the «Crystalline Structure of Metals," Phil. Trans. Roy. Soc. cxciii. photographic plate.

A practised observer can See also:

focus on a plate 1353 and cxcv. 279; F. Osmond, " See also:Crystallography of Iron," Annales of clear glass by the aid of a subsidiary low-power microscope See also:des Mines (See also:January ,9o0) ; Le Chatelier, Technology of Metallolens. If a semi-transparent plate is employed it should be as fine graphs," Metallogr¢phist, vol. iv. No. 1; Contribution a l'etude des as possible. The surface of the table is cut in such a way near H alliages. Societe d'encour¢gement pour l'industrie nationale (1901); See also:Smeaton, " Notes on the Etching of Steel Sections," Iron and Steel that the observer who is seated may conveniently examine the See also:Magazine, vol. ix. No. 3. (W. C.

R.-A.; F. H. NE.) object on the stage of the microscope, the portion B turning METALLURGY, the See also:

art of extracting metals from their ores; aside for this purpose. The subsequent focusing is effected by a the See also:term being customarily restricted to commercial as opposed See also:rod, FFF, and gearing attached to the fine See also:adjustment of the to laboratory methods. It is convenient to treat See also:electrical processes of extraction as forming the subjects of See also:Electrochemistry and See also:Electrometallurgy (qq.v.). The following table enumerates in the order of their importance the metals which,our subject at See also:present is understood to include; the second See also:column gives the chemical characters of the ores utilized, italics indicating those of subordinate importance. The term " oxide " includes carbonate, See also:hydrate, and, when marked with*, silicate. Metal. See also:Character of Ores. Iron Oxides, sulphide. Copper Complex sulphides, also oxides, metal. Silver Sulphide and reguline metal, chloride.

See also:

Gold Reguline metal. Lead Sulphide and basic carbonate, sulphate, &c. See also:Zinc Sulphide, oxide.* See also:Tin Oxide. Metallographist, vol. i. No. 3; " Metallography applied to Foundry Work," The Iron and Steel Magazine, vol. ix. No. 6, and vol. x. No. 1; J. E. See also:Stead, " Crystalline Structure of Iron and Steel," Journ.

Iron and Steel Inst. (1898), i. 145; " See also:

Practical Metallography," Prot. See also:Cleveland Inst. of See also:Engineers (Feb. 26, 1900) ; See also:Ewing and Rosenhain, microscope, GA; flap J when raised forms the support of the See also:lamp used for illumination. As an illuminant an arc See also:light has many advantages, as the exposure of the plate used will seldom exceed to seconds. The filament of a Nernst lamp can be used as the source of light; though not so brilliant as the arc it possesses the great See also:advantage of perfect immobility. For the best results, especially with high powers, the source of light must be small, so that its See also:image can be focussed on to the surface of the object; this advantage is possessed by both of these illuminants. Next in value comes the See also:acetylene See also:flame, and an incandescent lamp or a See also:gas lamp with a See also:mantle will give good results, but with much longer exposure. Actual illumination is best effected by a See also:Beck See also:vertical illuminator or a Zeiss See also:prism. It is necessary that the lens used for concentrating the light on the illuminator General Sequence of Operations.—Occasionally, but rarely, Sulphides.—Iron, copper, lead, zinc, See also:mercury, silver and See also:antimony very frequently present themselves in this See also:state of See also:combination, as metallic ores occur as practically pure compact masses, from components of a See also:family of ores which may be divided into two which the accompanying See also:matrix or " See also:gangue " can be detached sections: (L)' such as substantially consist of simple sulphides, as by See also:hand and See also:hammer. In most cases the " ore " (see See also:MINERAL, iron See also:pyrites (FeS2), See also:galena (See also:PbS), zinc See also:blende (ZnS), See also:cinnabar (HgS) ; DEPOSITS; See also:VEINS), as it comes out of the mine or See also:quarry, is and (2) complex sulphides, such as the various kinds of sulphureous simply mixture of ore and in which the latter copper ores (all substantially compounds or mixtures of sulphides a m proper gangue, of copper and iron) ; See also:bournonite, a complex sulphide of lead, See also:anti-not unfrequently predominates.

Hence it is generally necessary mony and copper; rothgiltigerz, sulphide of silver, antimony, and to purify the ore before the liberation of the metal is attempted. See also:

arsenic; fahlerz, sulphides of arsenic and antimony, combined with Most metallic ores are specifically heavier than the accompanying sulth ide es of and otherrsul ver, i wi, zinone c, another' silver; and mixtures impurities and their See also:purification is generally effected by reducing In treating a sulphureous ore, the first step as a See also:rule is to subject the crude ore to a fine enough See also:powder to detach the metallic it to oxidation by roasting it in a reverberatory or other See also:furnace, from the earthy See also:part, and then washing away the latter by a which leads to the burning away of at least part of the arsenic and current of water, as far as possible (see ORE-DRESSING). part of the See also:sulphur. The effect on the several individual metallic The See also:majority of ores being chemical compounds, the extraction sulphides (supposing only one of these to be present) is as follows: — g L. Those of silver (Ag2S) and mercury (HgS) yield sulphur dioxide of their metals demands chemical treatment. The chemical gas and metal; in the case of silver, sulphate is formed at low See also:tern- operations involved may be classified as follows:— peratures. Metallic mercury, in the circumstances, goes off as a 1. Fiery Operations.—The ore, generally with some " See also:flux," vapour, which is collected and condensed; silver -remains as a See also:regulus, is exposed to the See also:action of See also:fire. The fire in most cases has a but pure sulphide of silver is hardly ever worked. 2. Sulphides of iron and zinc yield the oxides Fe20a and ZnO as chemical, in addition to its See also:physical, See also:function. Moreover the final products, some basic sulphate being formed at the earlier stages, furnace (q.v.) is designed so as to facilitate the action of the See also:heat especially in the case of zinc. The oxides can be reduced by See also:carbon. and furnace gases in the desired direction. It is intended either 3.

The sulphides of lead and copper yield, the former a mixture to See also:

burn away certain components of the ore—in which case it of oxide and normal sulphate, the latter one of oxide and basic sulphate. Sulphate of lead is See also:stable at a red heat; sulphate of copper must be so regulated as to contain a sufficient excess of unburned breaks up into oxide, sulphur dioxide and See also:oxygen. In practice, oxygen; or it is meant to deoxidize (" reduce ") the ore,when the neither oxidation process is ever pushed to the end; it is stopped See also:draught must be restricted so as to keep the ore constantly as soon as the mixture of roasting-product and unchanged sulphide d up in combustible flame gases (carbon monoxide, contains oxygen and sulphur in the ratio of 02 : S. The See also:access of wrapped is then stopped and the whole heated to a higher temperature, See also:hydrogen, See also:marsh-gas, &c.). The majority of the chemical when the whole of the sulphur and oxygen is eliminated. This operations of metallurgy fall into this See also:category, and in these method is largely utilized in the smelting of lead from galena and of processes other metal-reducing agents than those naturally copper from copper pyrites. contained in the fire (or blast) are only exceptionally employed. 4. Sulphide of antimony, when roasted in air, is converted into a See also:kind of alloy of sulphide and oxide; the same holds for iron, only 2. Amalgamation.—The ore by itself (if it is a reguline one), its oxysulphide is quite readily converted into the pure oxide. Fe2Oa or with certain reagents (if it is not), is worked up with mercury by further roasting. Oxysulphide of antimony, by suitable processes so that the metal is obtained as an See also:amalgam, which can be separ- can be reduced to metal, but these processes are rarely used, because ated mechanically from the dross.

The purified amalgam is the same end is far more easily obtained by " precipitation," i.e. withdrawing the sulphur by See also:

fusion with metallic iron, forming distilled, when the mercury is recovered as a distillate while the metallic antimony and sulphide of iron. Both products fuse, but metal remains. readily part, because fused antimony is far heavier than fused 3. Wet Processes.—Strictly speaking, certain amalgamation sulphide of iron. A precisely similar method is used occasionally methods fall under this See also:head; but, in its See also:ordinary See also:acceptance, the for the reduction of lead from galena. Sulphide of lead, when fused term refers to processes in which the metal is extracted either ao egulus (it= LPb) and a " See also:mat " FeS which, ho ever,See also:Ion cooling, from the natural ore, or from the ore after roasting or other decomposes into the ordinary sulphide FeS,.and finely divided iron. preliminary treatment, by an acid or See also:salt solution, and from this What we have been explaining are See also:special cases of a more general solution precipitated—generally in the reguline form—by some metallurgic proposition: Any one of the metals, copper, iron, tin, zinc, lead, silver, antimony, arsenic, in general, is capable of de-suitable reagent. sulphurizing (at least partially) any of the others that follows it in Few methods of metal extraction at once yield a pure product. the series just given, and it does so the more readily and completely What as a rule is obtained is a more or less impure metal, which the greater the number of intervening terms. Hence, supposing requires to be "refined " to become See also:fit for the See also:market. a See also:complete mixture of these metals to be melted down under circum- stances admitting of only a partial sulphuration of the whole, the Chemical Operations.—Amalgamation and wet-way processes copper has the best See also:chance of passing into the " mat," while the have limited applications, being practically confined to copper, gold arsenic is the first to be eliminated as such, or, in the presence of and silver. We therefore here confine ourselves, in the main, to oxidants, as oxide. pyro-chemical operations. Arsenides.—Although arsenides are amongst the commonest The method to be adopted for the extraction of a metal from its impurities of ores generally, ores consisting essentially of arsenides ore is determined chiefly, though not entirely, by the nature of the are comparatively rare. The most important are certain See also:double non-metallic component with which the metal is combined. The arsenides of See also:cobalt and See also:nickel, which in practice are always See also:con-simplest case is that of the reguline ores where there is no non- taminated with the arsenides or other compounds of See also:foreign metals, metallic See also:element.

The important case is that of gold. such as iron, See also:

manganese, &c. The general mode of working these Oxides, Hydrates, See also:Carbonates and Silicates.—All iron and tin ores ores is as follows. The ore is first roasted by itself, when a part of proper fall under this heading, which, besides, comprises certain ores the arsenic goes off as such and as oxide, while a complex of lower of copper, of lead and of zinc. 1'he first step consists in subjecting arsenides remains. This See also:residue is now subjected to careful oxidisx, the crude ore to a roasting or calcining process, the object of which See also:ing fusion in the presence of some solvent for metallic bases. The is to remove the water and carbon dioxide, and burn away, to some effect is that the several metals are oxidized away and pass into the extent at least, the sulphur, arsenic or organic See also:matter. The residue slag (as silicates) in the following order—manganese, iron, cobalt, consists of an impure oxide of the respective metal, which in all cases nickel; and at any stage the as yet unoxidized residue of arsenide is reduced by treatment with See also:fuel at a high temperature. Should assumes the form of a fused regulus, which sinks down through. the the metal be present as a silicate, See also:lime must be added in the smelting slag as a " speis." (This term has the same meaning in reference to remove the See also:silica and liberate the oxide. to arsenides as " mat " has in regard to sulphides.) By stopping The temperature required for the reduction of zinc lies above the the process at the right moment, we can produce a speis which boiling point of the metal; hence the mixture of ore and reducing contains only cobalt and nickel, and if at this stage also the flux is See also:agent (See also:charcoal is generally used) must be heated in a,See also:retort combined renewed we can further produce a speis which contains only nickel with condensing apparatus. In all the other cases the reduction and a slag which substantially is one of cobalt only. The composiis effected in the fire itself, a See also:tower-shaped blast furnace being pre- tion of the speises generally varies from AsMe 812 to AsMe2, where ferably used. The furnace is charged with alternate layers of fuel " Me " means one atomic See also:weight of metal in toto, so that in general and ore (or rather ore and flux, see below), and the whole kindled 'Me = xFe + yCo + zNi, where x + y + z = I. The siliceous Metal.

Character of Ores. Mercury . . Sulphide, reguline metal. Antimony . Sulphide. See also:

Bismuth ..... Reguline metal. Nickel and cobalt . Arsenides. See also:Platinum, See also:iridium, &c. . Reguline. from below.

The metallic oxide, partly by the See also:

direct action of the carbon with which it is in contact, but principally by that of the carbon monoxide produced in the lower strata from the oxygen of the blast and the hot carbon there, is reduced to the metallic state; the metal fuses and runs down, with the slag, to the bottom of the furnace, whence both are withdrawn by opening plug-holes. cobalt is utilized as a blue pigment called " smalt "; the nickel-speis is worked up for metal. See also:Minor Reagents.—Besides the oxidizing and reducing agents present in the fire, and the " fluxes " added for the See also:production of slags, various minor reagents may be noticed. Metallic iron as a desulphurizer has already been referred to. Oxide of lead, PbO (litharge), is largely used as an oxidizing agent. At a red heat, when it melts, it readily attacks all metals, except silver and gold, the general result being the formation of a mixed oxide and of a mixed regulus, a See also:distribution, in other words, of both the lead and the metal acted on between slag and regulus. More important is its action on metallic sulphides, which, in general, results in the formation of three things besides sulphur dioxide, viz. a mixed oxide slag including the excess of litharge, a regulus of lead (which may include bismuth and other more readily reducible metals), and, if the litharge is not sufficient for a complete oxidation, a " mat " comprising the more readily sulphurizable metals. Oxide of lead, being a most powerful solvent for metallic oxides generally, is also largely used for the separation of silver or gold from base metallic oxides. Metallic lead is to metals generally what oxide of lead is to metallic oxides. It accordingly is available as a solvent for taking up small particles of metal diffused throughout a mass of slag, and uniting them into one regulus. This leads us to the process of " cupellation," which serves for the extraction of gold (q.v.; see also See also:ASSAYING) and silver from their alloys with base metals. Fluxes.—All ores are contaminated with more or less gangue, which in general consists of infusible matter, and if left unheeded in the reduction of the metallic part of the ore would retain more or less of the metal disseminated through it, or at best foul the furnace.

To avoid this, the ore as it goes into the furnace is mixed with " fluxes " so selected as to convert the gangue into a fusible. " slag," which readily runs down through the fuel with the regulus and separates from the latter. The quality and proportion of flux should, if possible, be so chosen that the formation of the slag sets in only after the metal has been reduced and molten; or else part of the basic oxide of the metal. to be extracted may be dissolved by the slag and its reduction thus be prevented or retarded. Slags are not a necessary evil; if an ore were See also:

free from gangue we should add gangue and flux from without to produce a slag, because one of its functions is to form a layer on the regulus which protects it against the further action of the blast or furnace gases. Fluxes may be arranged under the three heads of (I) fluor-spar, (2) basic fluxes and (3) acid fluxes. Fluor-spar fuses up at a red heat with silica, sulphates of calcium and See also:barium, and a few other infusible substances into homogeneous masses. It shows little tendency to dissolve basic oxides, such as lime, &c. One part of fluor-spar liquefies about half a part of silica, four parts of calcium sulphate and one and a half parts of barium sulphate. Upon these facts its extremely wide application in metallurgy is founded. Carbonate of soda (or potash is the most powerful basic flux. It dissolves silica and all silicates into fusible glasses. On the other hand, See also:borax may be taken as a type for the acid fluxes.

At a red heat, when it forms a viscid fluid, it readily dissolves all basic oxides into fusible complex borates. Now the gangue of an ore in general consists either of some basic material such as carbonate of lime (or See also:

magnesia), ferric oxide, alumina, &c., or of silica (See also:quartz) or some more or less acid silicate, or else of a mixture of the two classes of bodies. So any kind of gangue might be liquefied by means of borax or by means of alkaline carbonate; but neither of the two is used otherwise than for assaying; what the metal-smelter does is to add to a .basic gangue the proportion of silica, and to an acid ore the proportion of lime, or, indirectly, of ferrous or perhaps manganous oxide, which it may need for the formation of a slag of the proper qualities. The slag must possess the proper degree of saturation. In other words, taking SiO2+ nMeO (where MeO means an See also:equivalent of base) as a See also:formula for the potential slag, n must have the proper value. If n is too small, i.e. if the slag is too acid, it may dissolve part of the metal to be recovered; if n is too great, i.e. the slag too basic, it may refuse to dissolve, for instance, the ferrous oxide which is meant to go into it, and this oxide will then be reduced, and its metal (iron in our example) contaminate the regulus. In reference to the problem under discussion, it is See also:worth noting that oxides of lead and copper are more readily reduced to metals than oxide of iron Fe203 is to FeO, the latter more readily to FeO than FeO itself to metal, and FeO more readily to metal than manganous oxide is. Oxide of calcium (lime) is not reducible at all. The order of basicity in the oxides (their readiness to go into the slag) is precisely the See also:reverse. Most slags being, as we have seen, complex silicates, it is a most important problem of scientific metallurgy to determine the relations in this class of bodies between chemical See also:composition on the one hand and fusibility and solvent power for certain oxides (CaO, FeO, Fe2Oi, Al203, SiO2, &c.) on the other. Their general composition may be expressed as n(MO-f-xSiO2)+m[(fe or al)O +xSiO2] (M=Ca, Mg, Fe, K2, &c.; fe =Fe, al=;Al.) The following mode of classifying and naming composition in silicates is metallurgical; scientific chemists designate Class I. as orthosilicates, Class II. as metasilicates, Class III. as sesquisilicates. In the formulae M stands for K2, Ca, Fe, &c., or for al=fAl, fe=;Fe, &c.

Name. Formula. Oxygen Ratio. x I. Singulo-silicates ISiOi+IMO tease. Acid. ` 1 i . ISi0ii-IMO i 2 I II. . . Bi-silicates It should be possible to represent each quality of a silicate as a function of x, n/m, and of the nature of the individual bases that make up the MO and (fe or al) 0 respectively. Our actual knowledge falls far See also:

short of this possibility. The problem, in fact, is very difficult, the more so as it is complicated by the existence of aluminates, compounds such as Al203. 3CaO, in which the alumina plays the part of acid, and the occasional existence of compounds of fluorides and silicates in certain slags.

The formation of slags, or, what comes to the same thing, of metallic silicates, was especially studied by See also:

Percy, See also:Smith, Bischof, See also:Plattner and others, and in more recent times by See also:Vogt, Doelter, and at the Geophysical laboratory of the See also:Carnegie Institution, See also:Washington. METAL-WORK. Among the many stages in the development of primeval See also:man, none can have been of greater moment in his struggle for existence than the See also:discovery of the metals, and the means of working them. The names generally given to the three prehistoric periods of man's See also:life on the See also:earth—the See also:Stone, the See also:Bronze and the Iron age—imply the vast importance of the progressive steps from the See also:flint See also:knife to the bronze See also:Celt, and lastly to the keen-edged elastic iron weapon or See also:tool. The metals chiefly used in the arts have been gold, silver, copper and tin (the last two generally mixed, forming an alloy called bronze), iron and lead (see the See also:separate articles on these metals). Their peculiarities have naturally marked out each of them for special uses and methods of treatment. The durability and the extraordinary ductility and pliancy of gold, its power of being subdivided, See also:drawn out or flattened into See also:wire or See also:leaf of almost See also:infinite fineness, have led to its being used for See also:works where great minuteness and delicacy of See also:execution were required; while its beauty and rarity have, for the most part, limited its use to objects of adornment and luxury, as distinct from those of utility. In a lesser degree most of the qualities of gold are shared by silver, and consequently the treatment of these two metals has always been very similar, though the greater abundance of the latter metal has allowed it to be used on a larger See also:scale and for a greater variety of purposes. The great fluidity of bronze when melted, the slightness of its contraction on solidifying, together with its See also:density and hardness, make it especially suitable for casting, and allow of its taking the impress of the See also:mould with extreme sharpness and delicacy. In the form of plate it can be tempered and annealed till its See also:elasticity and toughness are much increased, and it can then be formed into almost any shape under the hammer and See also:punch. By other methods of treatment, known to the See also:ancient Egyptians, Greeks and others, but now forgotten, it could be hardened and formed into knife and See also:razor edges of the utmost keenness. In many specimens of ancient bronze, small quantities of silver, lead and zinc have been found, but their presence is probably accidental.

In See also:

modern times See also:brass has been much used, chiefly for the See also:sake of its cheapness as compared with bronze. In beauty, durability and delicacy of surface it is very inferior to bronze, and, though of some commercial importal CE, has been of but little use in the production of works of art. To some extent copper was used in an almost pure state during See also:medieval times, especially from the 12th to the 15th See also:century, mainly for objects of ecclesiastical use, such as pyxes, monstrances, reliquaries and croziers, partly on account of its softness under the tool, and also because it was slightly easier to. apply See also:enamel and See also:gilding to pure copper than to bronze (see fig. I). In the medieval See also:period it was used to some extent in the shape of thin sheeting for See also:roofs, as at St See also:Mark's, See also:Venice; while during the 16th and 17th centuries it was largely employed for ornamental domestic vessels of various sorts. Iron.'--The abundance in which iron is found in so many places, its great strength, its remarkable ductility and malleability in a red-hot state, and the ease with which two heated surfaces of iron can be welded together under the hammer combine to make it specially suitable for works on a large scale where strength with lightness are required —things such as screens, window-grills, ornamental hinges and the like. In its hot plastic state iron can be formed and modelled under the hammer to almost any degree of refinement, while its great strength allows it to be beaten out into leaves and ornaments of almost paper-like thinness and delicacy. With repeated hammering, See also:drawing out and See also:annealing, it gains much in strength and toughness, and the addition of a very minute quantity of carbon converts it into steel, less tough, but of the keenest hardness. The large employment of cast iron is comparatively modern, in See also:England at least only dating from the 16th century; it is not, however, in-capable of See also:artistic treatment if due regard be paid to the necessities of casting, and if no See also:attempt is made to imitate the fine-drawn lightness to which wrought iron so readily lends itself. At the best, however, it is not generally suited for the finest work, as the great contraction of iron in passing from the fluid to the solid state renders the cast somewhat See also:blunt and spirit-less. Among the Assyrians, See also:Italian work of the 15th century. Egyptians and Greeks the use of iron, either cast or wrought, was very limited, bronze being the favourite metal almost for all purposes.

The difficulty of smelting the ore was probably one See also:

reason for this, as well as the now forgotten skill which enabled bronze to be tempered to a steel-like edge. It had, however, its value, of which a See also:proof occurs in See also:Homer (Il. See also:xxiii.), where a mass of iron is mentioned as being one of the prizes at the funeral See also:games of Patroclus. Methods of Manipulation in Metal-Work.—Gold, silver and bronze may be treated in various ways, the See also:chief of which are (1) casting in a mould, and (2) treatment by hammering and punching (Fr. repousse). The first of these, casting is chiefly adapted for bronze, or ' Analyses of the iron of prehistoric weapons have brought to light the interesting fact that many of these earliest specimens of iron manufacture contain a considerable percentage of nickel. This special alloy does not occur in any known iron ores, but is invariably found in meteoric iron. It thus appears that iron was manufactured from meteorolites which had fallen to the earth in an almost pure metallic state, possibly See also:long before prehistoric man had learnt how to dig for and See also:smelt iron in any of the forms of ore which are found on this See also:planet.in the case of the more See also:precious metals only if they are used on a very small scale. The reason of this is that a repousse relief is of much thinner substance than if the same See also:design were cast, even by the most skilful metal-worker, and so a large surface may be produced with a very small See also:expenditure of valuable metal. Casting is probably the most See also:primitive method of metal-work. This has passed through three stages, the first being represented by solid castings, such as are most celts and other implements of the prehistoric time; the mould was formed of See also:clay, See also:sand or stone, and the fluid metal was poured in till the hollow was full. The next stage was, in the case of bronze, to introduce an iron core, probably to See also:save needless expenditure of the more valuable metal. The British Museum possesses an interesting See also:Etruscan or Archaic Italian example of this primitive See also:device. It is a bronze statuette from Sessa on the See also:Volturno, about 2 ft. high, of a See also:female See also:standing, robed in a See also:close-fitting See also:chiton.

The presence of the iron core has been made visible by the splitting of the figure, owing to the unequal contraction of the two metals. The forearms, which are extended, have been cast separately and soldered or brazed on to the elbows. The third and last stage in the progress of the art'of casting was the employment of a core, generally of clay, See also:

round which the metal was cast in a See also:mere skin, only thick enough for strength, without See also:waste of metal. The Greeks and See also:Romans attained to the greatest possible skill in this process. Their exact method is not certainly known, but it appears probable that they were acquainted with the process now called d cire perdue—the same as that employed by the great Italian artists in bronze. See also:Cellini, the great Florentine artist of the 16th century, has described it fully in his Trattato della Scultura. If a statue was to be cast, the figure was first roughly modelled in clay—only rather smaller in all its dimensions than the future bronze; all over this a skin of See also:wax was laid, and worked by the sculptor with modelling tools to the required form and finish. A mixture of pounded See also:brick, clay and ashes was then ground finely in water to the consistence of cream, and successive coats of this mixture were then applied with a See also:brush, till a second skin was formed all over the wax, fitting closely into every, See also:line and depression of the modelling. Soft clay was then carefully laid on to strengthen the mould, in considerable thickness, till the whole statue appeared like a shapeless mass of clay, round which iron hoops were See also:bound to hold it all together. The whole was then thoroughly dried, and placed in a hot See also:oven, which baked the clay, both of the core and the outside mould, and melted the wax, which was allowed to run out from small holes made for the purpose. Thus a hollow was left, corresponding to the skin of wax between the core and the mould, the relative positions of which were preserved by various small rods of bronze, which had previously been driven through from the See also:outer mould to the rough core. The mould was now ready, and melted bronze was poured in till the whole space between the core and the outer mould was full.

After slowly cooling, the outer mould was broken away from outside the statue and the inner core as much as possible broken up and raked out through a hole in the See also:

foot or some other part of the statue. The projecting rods of bronze were then cut away, and the whole finished by rubbing down and polishing over any roughness or defective places. The most skilful sculptors, however, had but little of this after-touching to do, the final modelling and even polish which they had put upon the wax being faithfully reproduced in the bronze casting. The further enrichment of the objeet„ by enamels and inlay of other metals was practised at a very See also:early period by See also:Assyrian, See also:Egyptian and See also:Greek metal-workers, as well as by the artists of See also:Persia and medieval See also:Europe. The second chief process, that of hammered work (Gr. uLupilkaros; Fr. repousse), was probably adopted for bronze-work on a large scale before the art of forming large castings was discovered. In the most primitive method thin plates of bronze were hammered over a wooden core, rudely cut into the required shape, the core serving the double purpose of giving shape to and strengthening the thin metal. A further development in the art of hammered work consisted in laying the metal plate on a soft and elastic See also:bed of See also:cement. made of See also:pitch and pounded brick. The design was then beaten into relief from the back with hammers and punches, the pitch bed yielding to the protuberances which were thus formed, and serving to prevent the punch from breaking the metal into holes. The pitch was then melted away from the front of the embossed relief, and applied in a similar way to the back, so that the modelling could be completed on the See also:face of the relief, the final touches being given by the graver. This process was chiefly applied by medieval artists to the precious metals, but by the Assyrians, Greeks and other early nations it was largely used for bronze. The great See also:gates of See also:Shalmaneser II., 858–823 B.C., from Balawat, now in the British Museum, are a remarkable example of this sort of work on a large scale, though the treatment of the reliefs is minute and delicate. The " Siris bronzes," in the same museum, are a most astonishing example of the skill attained by Greek artists in this repousse work (see BrSnsted's Bronzes of Siris, 1836).

They are a pair of See also:

shoulder-pieces from a suit of bronze See also:armour, and each has in very high relief a combat between a Greek See also:warrior and an See also:Amazon. No work of art in metal has probably ever surpassed these little figures for beauty, vigour and expression, while the skill with which the artist has beaten these high reliefs out of a See also:flat plate of metal appears almost miraculous. The heads of the figures are nearly detached from the ground, their substance is little thicker than paper, and yet in no place has the metal been broken through by the punch. They are probably of the school of See also:Praxiteles, and date from the 4th century B.C. (see fig. 2). Copper and tin have been but little used separately. Copper in its pure state may be worked by the same methods as bronze, but it is inferior to it in hardness, strength and beauty of surface. Tin is too weak and brittle a metal to be employed alone for any but small objects. Some considerable number of tin drinking-cups and See also:bowls, of the See also:Celtic period have been found in Cornwallin the neighbourhood of the celebrated tin and copper mines, which have been worked from a very early period. The use of lead has been more extended. In sheets it forms the best of all coverings for roofs and even See also:spires.

In the See also:

Roman and medieval periods it was largely used for coffins, which were often richly ornamented with cast work in relief. Though fusible at a very low temperature, and very soft, it has great power of resisting decay from See also:damp or exposure. Its most important use in an artistic form has been in the shape of baptismal fonts, chiefly between the 11th and the 14th centuries. The See also:superior beauty of colour and durability of old specimens of lead is owing to the natural presence of a small proportion of silver. Modern smelters carefully See also:extract this silver from the lead ore, thereby greatly impairing the durability and beauty of the metal. As in almost all the arts, the ancient Egyptians excelled in their metal-work, especially in the use of bronze and the precious metals. These were worked by casting and hammering, and ornamented by inlay, gilding and enamels with the greatest possible skill. From See also:Egypt perhaps was derived the early skill of the See also:Hebrews. Further instruction in the art of metal-working came probably to the See also:Jews from the neighbouring See also:country of See also:Tyre. The description of the great gold lions of See also:Solomon's See also:throne, and the laver of cast bronze supported on figures of oxen, shows that the artificers of that time had overcome the difficulties of metal-working and See also:founding on a large scale. The Assyrians were perhaps the most remarkable of all ancient nations for the See also:colossal See also:size and splendour of their works in metal; whole See also:circuit walls of great cities, such as See also:Ecbatana, are said to have been covered with metal plates, gilt or silvered. See also:Herodotus, See also:Athenaeus and other Greek and Roman writers have recorded the enormous number of colossal statues and other works of art for which See also:Babylon and See also:Nineveh were so famed.

The numerous objects of bronze and other metals brought to light by the excavations in the See also:

Tigris and See also:Euphrates valleys, though mostly on a small scale, See also:bear See also:witness to the great skill and artistic power of the See also:people who produced them; while the discovery of some bronze statuettes, shown by See also:inscriptions on them to be not later than 2200 B.C., proves how early was the development of this See also:branch of art among the people of See also:Assyria. The metal-Work of See also:Greece.—The early See also:history of metal-working in Greece is extremely obscure, and archaeologists are divided in See also:opinion even on so important a question as the relative use of bronze and iron in the Homeric age. The See also:evidence of Mycenaean remains, as compared with the See also:literary evidence of Homer, is both inadequate and inconclusive (see See also:AEGEAN See also:CIVILIZATION; GREEK ART; ARMS AND ARMOUR, Ancient; PLATE; &e.). The poems of Homer are full of descriptions of elaborate works in bronze, gold and silver, which, even when full See also:allowance is made for poetic See also:fancy, show clearly enough very advanced skill in the working and ornamenting of these metals. Homer's description of the See also:shield of See also:Achilles, made of bronze, enriched with bands of figure reliefs in gold, silver and tin, could hardly have been written by a man who had not some See also:personal acquaintance with works in metal of a very elaborate kind. Again, the accuracy of his descriptions of brazen houses—such as that of See also:Alcinous, Od. vii. 81—is See also:borne witness to by See also:Pausanias's mention of the bronze See also:temple of See also:Athena XaXKiocKOS in See also:Sparta, and the bronze chamber dedicated to See also:Myron in 648 B.e., as well as by the discovery of the stains and bronze nails, which show that the whole interior of the so-called See also:treasury of See also:Atreus at See also:Mycenae was once covered with a lining of bronze plates. Of the two chief methods of working bronze, gold and silver, it is probable that.the hammer process was first practised, at least for statues, among the Greeks, who themselves attributed the invention of the art of hollow casting to See also:Theodorus and See also:Rhoecus, both Samian sculptors, about the See also:middle of the 6th century B.C. Pausanias specially mentions that one of the See also:oldest statues he had ever seen was a large figure of See also:Zeus in Sparta, made of hammered bronze plates riveted together. With increased skill in large castings, and the discovery of the use of cores, by which the fluid bronze was poured into a mere skin-like cavity, hammered or repousse work was only used in the case of small objects in which lightness was desirable, or for the precious metals in order to avoid large expenditure of metal. The colossal statues of See also:ivory and gold by See also:Pheidias were the most notable examples of this use of gold, especially his statue of Athena in the See also:Parthenon, and the one of Zeus at See also:Olympia. The nude parts, such as face and hands, were of ivory, while the armour and drapery were of beaten gold.

The comparatively small weight of gold used by Pheidias is very remarkable when the great size of the statues is considered. A graphic See also:

representation of the workshop of a Greek sculptor in bronze is given on a fictile See also:vase in the See also:Berlin Museum (see See also:Gerhard's Trinkschalen, plates xii., xiii.). One man is raking out the fire in a high furnace, while another behind is blowing the See also:bellows. Two others are smoothing the surface of a statue with scraping tools, formed like a strigil. A See also:fourth is beating the See also:arm of an unfinished figure, the head of which lies at the workman's feet. Perhaps the most important of early Greek works in cast bronze,. both from its size and great See also:historical interest, is the bronze See also:pillar (now in the See also:Hippodrome at See also:Constantinople) which was erected to commemorate the victory of the allied Greek states over the Persians at See also:Plataea in 479 B.C. (see See also:Newton's Travels in the See also:Levant). It is in the form of three serpents See also:twisted together, and before the heads were broken off was at least 20 ft. high. It is cast hollow, all in one piece, and has the names of the allied states engraved on the lower part of the coils. Its size and the beauty of its surface show great technical skill in the founder's art. On it once stood the gold See also:tripod dedicated to See also:Apollo as a tenth of the spoils. It is described by both Herodotus and Pausanias.

See also:

Marble was comparatively but little used by the earlier Greek sculptors, and even Myron, a rather older man than Pheidias, seems to have executed nearly all his most important statues in metal. Additional richness was given to Greek bronze-work by gold or silver inlay on lips, eyes and See also:borders of the See also:dress; one remarkable statuette in the British Museum has eyes inlaid with diamonds and See also:fret-work inlay in silver on the border of the chiton. The mirrors of the Greeks are among the most important specimens of their artistic metal-work. These are bronze disks, one side polished to serve as a reflector, and the back ornamented with engraved outline drawings, often of great beauty (see Gerhard, Etruskiscke Spiegel, 1843-1867). In metal-work, as in other arts, the Romans were pupils and imitators of the Greeks. Owing to the growth of the spirit of luxury, a considerable demand arose for magnificent articles of gold and silver plate. The finest specimens of these that still exist are the very beautiful set of silver plate found buried near See also:Hildesheim in 1869, now in the Berlin Museum. They consist of drinking vessels, bowls, vases, ladles and other objects of silver, See also:parcel-gilt, and exquisitely decorated with figures in relief, both cast and repousse. There are electrotypes of these in the See also:Victoria and See also:Albert Museum. When the seat of the See also:empire was changed, See also:Byzantium became the chief centre for the production of artistic metal-work. From Byzantium the special skill in this art was transmitted in the 9th and loth centuries to the Rhenish provinces of See also:Germany and to See also:Italy, and thence to the whole of western Europe; in this way the 18th century smith who wrought the See also:Hampton See also:Court iron gates was the See also:heir to the mechanical skill of the ancient metal-workers of See also:Phoenicia and Greece. In that period of extreme degradation into which all the higher arts See also:fell after the destruction of the Roman Empire, though true feeling for beauty and knowledge of the subtleties of the human form remained for centuries almost dormant, yet at Byzantium at least there still survived great technical skill and power in the production of all sorts of metal-work.

In the age of Justinian (first half of the 6th century) the great See also:

church of St See also:Sophia at Constantinople was adorned with an almost incredible amount of See also:wealth and splendour in the form of screens, altars, candlesticks and other ecclesiastical See also:furniture made of massive gold and silver. Metal-Work in Italy.—It was therefore to Byzantium that Italy turned for metal-workers, and especially for goldsmiths, when, in the 6th to the 8th centuries, the See also:basilica of St See also:Peter's in See also:Rome was enriched with masses of gold and silver for decorations and fittings, the gifts of many donors from See also:Belisarius to See also:Leo III., the mere See also:catalogue of which reads like a See also:tale from the Arabian Nights. The gorgeous Pala d'oro, still in St Mark's at Venice, a gold See also:retable covered with delicate reliefs and enriched with enamels and jewels, was the work of See also:Byzantine artists during the 11th century. This work was in progress for more than a See also:hundred years, and was set in its place in rio6 A.D., though still unfinished (see Bellomo, Pala d'oro di St Marco, 1847). It was, however, especially for the production of bronze doors for churches, ornamented with panels of cast work in high relief, that Italy obtained the services of Byzantine workmen (see Garrucci, Arte cristiana, 1872-1882). One artist, named Staurachios, produced many works of this class, some of which still exist, such as the bronze doors of the See also:cathedral at See also:Amalfi, dated ro66 A.U. Probably by the same artist, though his name was spelled differently, were the bronze doors of See also:San See also:Paolo fuori le Mura, Rome, careful drawings of which exist, though the originals were destroyed in the fire of 1824. Other important examples exist at See also:Ravello (1197), See also:Salerno (1099), Amalfi (ro62), Atrani (1087); and doors at See also:Monreale in See also:Sicily and at See also:Trani, signed by an artist named Barisanos (end of the r 2th century); the reliefs on these last are remarkable for expression and dignity; in spite of their early rudeness of modelling and See also:ignorance of the human figure. Most of these works in bronze were enriched with fine lines inlaid in silver, and in some cases with a kind of See also:niello or enamel. The technical skill of these Byzantine metal-workers was soon acquired by native Italian artists, who produced many important works in bronze similar in See also:style and execution to those of the Byzantine Greeks. Such, for example, are the bronze doors of San Zenone at See also:Verona (unlike the others, of repousse; not cast work); those of the Duomo of See also:Pisa, cast in 118o by Bonannus, and of the Duomo of See also:Troia, the last made in the beginning of the 12th century by Oderisius of See also:Benevento. Another artist, named See also:Roger of Amalfi, worked in the same way; and in the See also:year r 219 the See also:brothers Hubertus and Petrus of See also:Piacenza cast the bronze See also:door for one of the side chapels in San Giovanni in Laterano.

One of the most important early specimens of metal-work is the gold and silver See also:

altar of Sant' Ambrogio in See also:Milan. In character of work and design it resembles the Venice Pala d'Oro, but is still earlier in date, being a See also:gift to the church from See also:Archbishop See also:Angilbert II. in 835 A.D. (see Du Sommerard, and D'See also:Agincourt, Moyen Age). It is signed wOLVINIVS MAGISTER PHABER; nothing is known of the artist, but he probably belonged to the semi=`~ Byzantine school of the See also:Rhine provinces; according to Dr See also:Rock he was an Anglo-Saxon See also:goldsmith. It is a very sumptuous work, the front of the altar being entirely of gold, with repousse reliefs and cloisonne enamels; the back and ends are of silver, with gold ornaments. On the front are figures of See also:Christ and the twelve apostles; the ends and back have reliefs illustrating the life of St See also:Ambrose. The most important existing work of art in metal of the 13th century is the great See also:candelabrum now in Milan Cathedral. It is of gilt bronze, more than 14 ft. high; it has seven branches for candles, and its upright See also:stem is supported on four winged dragons. For delicate and spirited execution, together with refined See also:grace-fulness of design, it is unsurpassed by any similar work of art. Every one of the numerous little figures with which it is adorned is worthy of study for the beauty and expression of the face, and the dignified arrangement of the drapery (see fig. 3). The semi-conventional open See also:scroll-work of branches and See also:fruit which See also:wind around and frame each figure or See also:group is devised with the most perfect See also:taste and richness of fancy, while each minute part of this great piece of metal-work is finished with all the care that could have been bestowed on the smallest article of gold jewellery.

Though something in the See also:

grotesque dragons of the base recalls the Byzantine school, yet the beauty of the figures and the keen feeling for graceful curves and folds in the drapery point to a native Italian as being the artist who produced this wonderful work of art. There is a cast in the Victoria and Albert Museum. Fro. 4.—Silver Repousse Reliefs from the See also:Pistoia Retable. During the 13th and 14th centuries in Italy the widespread See also:influence of Niccola See also:Pisano and his school encouraged the sculptor to use marble rather than bronze for his work. At this period wrought iron came into general use in the form of screens for chapels and tombs, and grills for windows. These are mostly of great beauty, and show remarkable skill in the use of the hammer, as well as power in adapting the design to the requirements of the material. Among the finest examples of this sort of work are the screens round the tombs of the Scala family at Verona, I350-1375, -a sort of network of light cusped quatrefoils, each filled up with a small See also:ladder (scala) in allusion to the name of the family. The most elaborate specimen of this wrought work is the See also:screen to the See also:Rinuccini See also:chapel in See also:Santa Croce, See also:Florence, of 1371, in which moulded pillars and window-like See also:tracery have been wrought and modelled by the hammer with extraordinary skill (see See also:Wyatt, Metal-Work of Middle Ages). Of about the same date are the almost equally magnificent screens in, Sta Trinita, Florence, and at See also:Siena across the chapel in the Palazzo Pubblico. The main part of most of these screens is filled in with quatrefoils, and at the See also:top is an open See also:frieze formed of plate iron pierced, repousse, and enriched with See also:engraving. In the 14th century great quantities of objects for ecclesiastical use wereproduced in Italy.

The silver altar of the Florence See also:

baptistery was begun in the first half of the 14th century, and not completed till after 1477 (see Gaz. des See also:beaux-arts, See also:Jan. 1883). The greatest artists in metal laboured on it in See also:succession, among them See also:Orcagna, See also:Ghiberti, Verrocchio, See also:Ant. See also:Pollaiuolo and many others. It has elaborate reliefs in repousse work, cast canopies and minute statuettes, with the further enrichment of translucent coloured enamels. The silver altar and retable of Pistoia Cathedral (see fig. 4), and the great See also:shrine at See also:Orvieto, are works of the same class, and of equal importance. Whole volumes might be devoted to the magnificent works in bronze produced by the Florentine artists of this century, works such as the baptistery gates by Ghiberti, the statues of Verrocchio, See also:Donatello and many others, the bronze screen in See also:Prato cathedral by See also:Simone, See also:brother of Donatello, in 1444-1461, and the screen and bronze ornaments of the See also:tomb of See also:Piero and Giovanni dei See also:Medici in San Lorenzo, Florence, by Verrocchio, in 1472. At the latter part of the 15th century and the beginning of the 16th the Pollaiuoli, See also:Ricci and other artists devoted much labour and artistic skill to the production of candlesticks and smaller objects of bronze, such as door-knockers, many of which are works of the greatest beauty. The candlesticks in the Certosa near See also:Pavia, and in the cathedrals of Venice and See also:Padua, are the finest examples of these. Niccolo See also:Grossi, who worked in wrought iron under the patronage of Lorenzo dei Medici, produced some wonderful specimens of metal-work, such as the candlesticks, lanterns, and rings fixed at intervals round the outside of the great palaces (see fig. 5).

The See also:

Strozzi See also:palace in Florence and the Palazzo del Magnifico at Siena have fine specimens of these — the former of wrought iron, the latter in See also:late 15th-century. Florentine work. cast bronze. At Venice fine work in metal, such as salvers andvases, was being produced, of almost See also:Oriental design, and in some cases the work of See also:resident Arab artificers. In the 16th century Benvenuto Cellini was supreme for skill in the production of enamelled jewellery, plate and even larger works of See also:sculpture (see Plon's See also:Ben. Cellini, 1882), and Giovanni de See also:Bologna in the latter part of the same century inherited to some extent the skill and artistic power of the great 15th-century artists. See also:Spain.—From a very early period the metal-workers of Spain have been distinguished for their skill, especially in the use of the precious metals. A very remarkable set of specimens of goldsmith's work of the 7th century are the eleven votive crowns, two crosses and other objects found in 1858 at Guarrazar, and now preserved at See also:Madrid and in See also:Paris in the See also:Cluny Museum (see Du Sommerard, Musee de Cluny, 1852). Magnificent works in silver, such as shrines, altar crosses and chf ch vessels of all kinds, were produced in Spain from the 14th to the 16th century—especially a number of sumptuous See also:tabernacles (custodia) for the See also:host, magnificent examples of which still exist in the cathedrals of See also:Toledo and See also:Seville. The bronze and wrought-iron screens—rejas, mostly of the 15th and 16th centuries—to be found in almost every important church in Spain are very fine examples of metal-work. They generally have moulded rails or balusters, and See also:rich friezes of pierced and repousse work, the whole being often thickly plated with silver. The See also:common use of metal for pulpits is a peculiarity Flo. 5.—Wrought-iron See also:Candle Pricket; of Spain; they are sometimes of bronze, as the pairs in See also:Burgos and Toledo cathedrals, or in wrought iron, like those at See also:Zamora and in the church of San Gil, Burgos.

The great candelabrum or tenebrarium in Seville Cathedral is the finest specimen of 16th-century metal-work in Spain; it was mainly the work of See also:

Bart. See also:Morel in 1562. It is of cast bronze enriched with delicate scroll-work foliage, and with See also:numbers of well-modelled statuettes. Especially in the art of metal-work Spain was much influenced in the 15th and 16th centuries by both Italy and Germany, so that numberless See also:Spanish objects produced at that time owe little or nothing to native designers. At an earlier period Arab and Moorish influence is no less apparent. 1 England.—In Saxon times the See also:English metal-workers, especially of the precious metals, possessed great skill, and appear to have produced shrines, altar-frontals, retables and other ecclesiastical furniture of considerable size and magnificence. See also:Dunstan, archbishop of See also:Canterbury (925-988), like Bernward, See also:bishop of Hildesheim a few years later, and St See also:Eloi of See also:France three centuries earlier, was himself a skilful worker in all kinds of metal. The description of the gold and silver retable given to the high altar of See also:Ely by See also:Abbot Theodwin in the 11th century, shows it to have been a large and elaborate piece of work decorated with many reliefs and figures in the round. In 1241 See also:Henry III. gave the order for the great gold shrine to contain the bones of See also:Edward the See also:Confessor. It was the work of members of the See also:Otho family, among whom the goldsmith's and coiner's crafts appear to have been long hereditary. Countless other imporant works • in the precious metals adorned every See also:abbey and cathedral church in the See also:kingdom. In the r3th century the English workers in wrought iron were especially skilful.

The grill over the tomb of See also:

Queen Eleanor at See also:Westminster, by See also:Thomas de Leghton, made about 1294, is a remarkable example of skill in See also:welding and modelling with the hammer (see fig. 6). The rich and graceful iron hinges, made often for small and out-of-the-way country churches, are a large and important class in the list of English wrought-iron work. Those on the See also:refectory door of Merton See also:College, See also:Oxford, are a beautiful and well-preserved example dating from the 14th century. More mechanical in execution, though still very rich in effect, is that sort of iron tracery work produced by cutting out patterns in plate, and superimposing one plate over the other, so as to give richness of effect by the shadowsproduced by these varying planes. The screen by Henry V.'s tomb at Westminster is a good early specimen of this kind of work. The screen to Bishop See also:West's chapel at Ely, and that round Edward VI.'s tomb at See also:Windsor, both made towards the end of the 15th century, are the most magnificent English examples of wrought iron; and much wrought-iron work of great beauty was produced at the beginning of the 18th century, especially under the superintendence of Sir See also:Christopher See also:Wren (see Ebbetts, Iron Work of 17th and 18th Centuries, r88o). Large flowing leaves of See also:acanthus and other See also:plants were beaten out with wonderful spirit and beauty of See also:curve. The gates from Hampton Court are the finest examples of this class of work (see fig. 7). From an early period bronze and See also:latten (a variety of brass) were much used in England for the smaller objects both of ecclesiastical and domestic use, but except for tombs and lecterns were but little used on a large scale till the 16th century. The full-length recumbent See also:effigies of Henry III. and Queen Eleanor at Westminster, cast in bronze by the " sire perdue " process, and thickly gilt, are equal, if not superior, in artistic beauty to any sculptor's work of the same period (end of the 13th century) that was produced in Italy or elsewhere.

These effigies are the work of an Englishman named See also:

William ToreL, The gates to Henry VII.'s chapel, and the screen round his tomb at Westminster (see fig. 8), are very elaborate and beautiful examples of " latter" work, showing the greatest technical skill in the founder's art. In latten also were produced the numerous monumental See also:brasses of which a large number still exist in England (see BRASSES, MONUMENTAL). In addition to its chief use as a roof covering, lead was some-times used in England for making fonts, generally tub-shaped, with figures cast in relief. Many examples exist: e.g. at Tidenham, See also:Gloucestershire; Warborough and See also:Dorchester Oxon; .Chirton, Wilts; and other places. Germany.—Unlike England, Germany in the loth and rich centuries produced large and elaborate works in cast bronze, especially doors for churches, much resembling the contemporary doors made in Italy under Byzantine influence. Bernward, bishop of Hildesheim, 992–1022, was especially skilled in this work, and was much influenced in design by a visit to Rome in the See also:suite of Otho III. The bronze column with winding reliefs now at Hildesheim was the result of his study of See also:Trajan's column, and the bronze door which he made for his own cathedral shows classical influence, especially in the composition of the drapery of the figures in the panels. The bronze doors of See also:Augsburg (1047–1072) are similar in style. The bronze tomb of See also:Rudolph of See also:Swabia in See also:Merseburg Cathedral (ro8o) is another fine work of the same school. The production of works in gold and silver was also carried on vigorously in Germany. The shrine of the three See also:kings at See also:Cologne is the finest surviving example.

At a later time Augsburg and See also:

Nuremberg were the chief centres for the production of artistic works in the various metals. See also:Hermann See also:Vischer, in the 15th century, and his son and grandsons were very remarkable as bronze founders. The See also:font at See also:Wittenberg, decorated with reliefs of the apostles, was the work of the See also:elder Vischer, while Peter and his son produced, among other important works, the shrine of St Sebald at Nuremberg, a work of great finish and of astonishing richness of fancy in its design. The tomb of See also:Maximilian I., and the statues round it, at See also:Innsbruck, begun in 1521, are perhaps the most meritorious See also:German work of this class in the 16th century, and show considerable Italian influence. In wrought iron the German smiths, especially during the 15th century, greatly excelled. Almost peculiar to Germany is the use of wrought iron for See also:grave-crosses and sepulchral monuments, of which the Nuremberg and other cemeteries contain fine examples. Many elaborate well-canopies were made in wrought iron, and gave full See also:play to the fancy and invention of the smith. The celebrated 15th-century example over the well at See also:Antwerp, attributed to Quintin See also:Matsys, is the finest of these. France.—From the time of the Romans the See also:city of See also:Limoges has been celebrated for all sorts of metal-work, and especially for brass enriched with enamel. In the 13th and 14th centuries many life-size sepulchral effigies were made of beaten copper or bronze, and ornamented by various-coloured " champleve enamels. The beauty of these effigies led to their being ported into England.; most are now destroyed, but a fine specimen still exists at Westminster on the tomb of William de See also:Valence (1296). In the ornamental iron-work for doors the See also:French smiths were pre-eminent for the richness of design and skilful treatment of their metal.

Probably no examples surpass those on the west doors of Notre See also:

Dame in Paris—unhappily much falsified by restoration. The crockets and finials on the fleches of See also:Amiens and Rheims are beautiful specimens of a highly ornamental treatment of cast lead, for which France was especially celebrated. In most respects, however, the development' of the various kinds of metal-working went through much the same stages as in England. Persia and See also:Damascus.—The metal-workers of the See also:East, especially in brass and steel, were renowned for their skill even in the time of See also:Theophilus, the monkish writer on the subject in the 13th century. But it was during the reign of Shah Abbas I. (d. 1628) that the greatest amount of skill both in design and execution was reached by the See also:Persian workmen. Delicate pierced vessels of gilt brass, enriched by tooling and. inlay of gold and silver, were among the chief specialties of the Persians (see fig. 9). A process called by Europeans " See also:damascening " (from Damascus, the chief seat of the export) was used to produce very delicate and rich surface See also:ornament. A pattern was incised with a graver in iron or steel, and then gold wire was beaten into the sunk lines, the whole surface being then smoothed and polished. In the time of Cellini this process was copied in Italy, and largely used, especially for the decoration of weapons and armour.

The repousse process both for brass and silver was much used by Oriental workers, and even now fine works of this class are. produced in the East, old designs still being adhered to. (J. H. M.) Modern Art Metal-Work.—The term " art metal-work " is applied to those works in metal in which beauty of form or decorative effect is the first See also:

consideration, irrespective of whether the object is intended for use or is merely ornamental; and it embraces any article from a See also:Birmingham brass bedstead to works of the highest artistic merit. The term, as definitely distinguishing one branch of metal-working from another, is objected to by many on the ground that no such prefix was required in the best periods of art, and that allied crafts continue to do without it to the present See also:day. Indeed, as long as metal-working remained a handicraft—in other words, until the introduction of See also:steam machinery—every article, however humble its purpose, seems to have been endowed with some traditional beauty of form. The robust, florid and distinctly Roman rendering of the classic, which followed the refined and attenuated treatment associated with the See also:architecture of the brothers See also:Adam, who died in 1792 and 1794, is the last development in England which can be regarded as a See also:national style. The massively moulded See also:ormolu See also:stair See also:balustrade of See also:Northumberland See also:House, now at 49 See also:Prince's See also:Gate; the candelabra at Windsor and See also:Buckingham Palace, produced in Birmingham by the firm of Messenger; the cast-iron railings with See also:javelin heads and See also:lictors' See also:fasces, the tripods, Corinthian column See also:standard lamps and candelabra, See also:boat-shaped oil lamps and See also:tent-shaped lustres with classic mountings, are examples of the metal-work of a style which, outside the See also:eccentric See also:Brighton See also:Pavilion and excursions into See also:Gothic and Elizabethan, was universally accepted in the See also:United Kingdom from the days of the Regency until after the See also:accession of Victoria. Except perhaps the silversmiths, no one was conscious of being engaged in " art metal-working," yet the See also:average is neither vulgar nor in See also:bad taste, and the larger works are both dignified and suited to their architectural surroundings. The introduction of gas as an illuminant, about 1816, at once induced a large demand and a novel description of metal fitting; and the See also:craft fell under the See also:control of a new commercial class, See also:intent on breaking with past traditions, and utilizing steam power, electyp-deposition, and every mechanical and scientific invention tending to economize metal or labour. But when all artistic See also:perception in Great See also:Britain appeared lost in admiration of the triumphs of machinery and the expansion of See also:trade, a new influence in art matters, that of the prince See also:consort, began to make itself See also:felt. The Great See also:Exhibition, state-aided See also:schools of design, the See also:South See also:Kensington Museum, and the See also:establishment of a See also:Science and Art See also:Department under See also:Government, were among the results of the important art revival which he inaugurated.

He is credited with having himself designed candelabra and other objects in metal, and he directly encouraged the production of the 'sumptuous See also:

treatise on metal-work by See also:Digby Wyatt, which laid the See also:foundations of the revival. To this work, and that of See also:Owen See also:Jones, can be traced the origin of theeclecticism which has laid all past styles of art under contribution. The Gothic revival also helped the recognition of art, without very directly affecting the See also:movement. It was valuable in teaching how to work within definite limitations, but without slavish copying; it also emancipated a considerable See also:body of craftsmen from the tyranny of manufacturers whose See also:sole See also:idea was that See also:machine-work should supersede handicraft. Its greatest efforts were the metal See also:chancel-screens designed by Sir G. G. See also:Scott, that for See also:Hereford Cathedral having been exhibited in 1862. It does not appear that the influence either of Owen Jones or Digby Wyatt on metal-working extended beyond bringing the variety and beauty of past styles to the direct See also:notice of designers. Neither can the See also:London silversmiths, though they employed the best See also:talent available, particularly in the See also:decade following the Great Exhibition of 1851, be credited with much influencing the art metal revival. They were rivalled by See also:Elkington of Birmingham, who secured the permanent assistance of at least one fine artist, Morel Ladeuil, the producer of the Elcho See also:Challenge Shield. Perhaps the first actual designer to make a lasting impression on the crafts was Thomas Jeckyll, some of whose work, including gates for See also:Sandringham, was exhibited in 1862. Infinitely greater as a designer was See also:Alfred See also:Stevens, whose influence on English craftsmen might be regarded as almost comparable to that of See also:Michelangelo on that of his Italian contemporaries.

Stevens's designs certainly directly raised the standard of production in several metal-working firms by whom he was employed; whilst in the See also:

Wellington Memorial in St See also:Paul's Cathedral, and in Dorchester House, his work is seen unfettered by commercial considerations. Omitting many whose occasional designs have had little influence on the development of the metal crafts, we come to Alfred See also:Gilbert, whose influence for a time was scarcely less than that of Stevens himself. Monumental works, such as his statue of Queen Victoria at See also:Winchester and his work at Windsor, may be handed down as his greatest achievements, but judged as art metal-work, his smaller productions, such as the centre-piece presented by the See also:army and See also:navy to Queen Victoria on her See also:Jubilee, have been more important. The charming bronze statuettes of See also:Onslow See also:Ford, the most representative of which are in the See also:Tate See also:Gallery; the work of See also:George Frampton, as seen in the See also:Mitchell Memorial; and the beautiful bas-reliefs of W. See also:Stirling See also:Lee, examples of which are the bronze gates of the Adelphi See also:Bank at See also:Liverpool, have all contributed, especially when applied to architectural decoration, to a high standard of excellence. Painters also have frequently designed and modelled for metal-work, for example, See also:Lord See also:Leighton, who produced bronze statuettes of most refined character; and Sir L. See also:Alma-Tadema, who designed the grilles for his studio and entrance See also:hall; but none so conspicuously as Professor H. von Herkomer, who, whether working in gold and enamel, iron, or his favourite alloy, See also:pewter, infuses a freshness into his designs and methods which displays an unusual mastery over materials. The gift of reproducing effects of nature or art by brush or See also:chisel is not necessarily accompanied by power to design; but a noteworthy exponent of the dual See also:faculty is G. C. Haite, whose designs are widely applied. It is chiefly to architecture that metal-work owes its permanent artistic improvement. In England buildings of See also:Norman See also:Shaw and Ernest George demanded quiet and harmonious metal-work; and the See also:custom of these architects of superintending and designing every detail, even for interiors, created the See also:supply.

The work of every worthy architect raises the standard of the crafts; but beyond others Messrs Ashbee, Lethaby and See also:

Wilson have taken an active personal interest in schools of metal-work. The technical schools have also been of immense service in creating a class of self-respecting craftsmen, whose See also:wages enable them to regard their work as worthy occupation abounding in interest. See also:Home See also:industries such as the metal-working round See also:Keswick (founded in 1884 by See also:Canon and Mrs Rawnsley), executed during See also:hours of idleness by See also:field labourers and railway porters, educate the passer-by as well as the worker. British architects and artists who design for the See also:principal metal-work has rather receded than progressed in merit, except when designed by architects and executed under their super-See also:vision. Though the demand for good domestic wrought-iron work has enormously increased, adaptations from the beautiful work of the 17th and 18th centuries have been found so suited to their architectural surroundings, that new departures have been relatively uncommon. Of such the gates for Sandringham, by Jeckyll; for See also:Crewe Hall, by See also:Charles See also:Barry; and for the Victoria and Albert Museum, by Gamble, are the earliest and best known. Of the vast number designed upon traditional lines may be cited those for Lambton See also:Castle, Welbeck, See also:Eaton Hall, See also:Twickenham, Clieveden, and the See also:Astor See also:Estate See also:Office on the Victoria See also:Embankment. Cast iron, brought to perfection by the See also:Coalbrookdale See also:Company about 186o, but now little esteemed, owing to the poverty of design which so often counterfeits smiths' work, presents great opportunities to founders possessing taste or willing to submit to artistic control. A very large field is also opening for cast-lead work, whether associated with architecture, as in the leaden covered-way over Northumberland See also:Street, in London (see Plate), and the fine See also:rain-water heads of the Birmingham See also:Law Courts (see Plate), or with the revival of the use of metal statuary and vases in gardens. The subdued colour and soft contours of pewter render it once more a favoured material, peculiarly adapted to the methods of the art revival, and perhaps destined to supersede electro-plate for See also:household purposes. In silver-work the proportion of new art designs exhibited by dealers and others is still relatively small; but jewellers, except when setting pure brilliants and pearls, are becoming more inclined to make their jewels of finely modelled gold and enamel enriched with precious and semi-precious stones, than of gems merely held together by wholly subordinate settings. On the See also:continent of Europe, France was the first to recognize the merits of its bygone designers and craftsmen, and even antecedent to the Exhibition of 1851, when art in Great Britain was dormant, it was possible to obtain in Paris faithful reproductions of the finest ormolu work of the 18th century.

At the same time a most active production of modern designs was proceeding, stimulated by rewards, with the result that the supply of clocks, lamps, candelabra, statuettes, and other ornaments in bronze and zinc to the See also:

rest of Europe became a mohopoly of Paris for nearly half a century. In all connected with their own homes the French adhere to their traditions far more than other nations, and the attempt at originality in the introduction of metal-work into the See also:scheme of decoration of a See also:room is almost unknown. In the domain of bronze and See also:imitation bronze statuary the originality of the French is absolutely unrivalled. And not only in bronze, but in Paris jewellery, enamels, silver, pewter and iron work a cultured refinement is apparent, beside which other productions, even the most finished, appear crude. The French artist attains his ideal, and it is difficult to imagine, from his standpoint, that the metal-work of the present can be surpassed. The best English metal-worker, on the contrary, is probably not often quite satisfied with the results he attains, perhaps because in Great Britain the pursuit of art has for centuries been fitful and individual, while in France art traditions are hereditary. The metal-work of See also:Belgium is based at ,present entirely on that of France, without attaining the same standard, unless designed for ecclesiastical uses. In See also:Holland these.,crafts have not progressed. Italian metal-workers are mainly employed in See also:reproduction; but traditions linger in some remote parts, while. the sporadic See also:appearance of craftsmen of a high order is eviderlCe that the ancient artistic spirit is not wholly See also:extinct. Similarly, the surprising damascening by Messrs Zuluaga of Madrid in the See also:monument to General See also:Prim, and that of See also:Alvarez of Toledo, give See also:hope that the Spanish craftsman only needs to be properly directed. German and See also:Austrian workers had for years shown more See also:energy than originality, but they have recently embraced the newest English developments and carried them to extremes of exaggeration. For really fresh and progressive indigenous art we may perhaps have, in the near future, to turn to See also:America decorating firms are to-day as conversant with the See also:Renaissance and succeeding styles of France and Italy as medieval revivalists were See also:familiar with the Gothic styles with which they made us so well acquainted.

Metal-work more or less based upon every kind of past style is produced in vast quantities, and in some cases so skilful are the workers that modern forgeries and reproductions are almost beyond the power of experts to detect. This large class of designers and craftsmen, to whom a thorough knowledge of the history of design is a See also:

necessity, follows and develops traditional lines. The new art school, on the contrary, breaks wholly with tradition, unless unconsciously influenced by the Japanese, and awards the highest place to originality in design. It is not to be expected that an art-revival following on, and in See also:possession of, all the results of a period of unprecedented activity in scientific See also:research should. proceed with the same See also:restraint as heretofore; but the unfettered activity, and the general encouragement to abandon the traditions of art, have no exact parallel in the past, and may yet prove a danger. It is perhaps the very rapidity of the movement that is likely to retard its progress, and to fail to carry with it the wealthy clients and the decorators they employ, or perhaps even to increase the disposition to cling to the reproductions of the styles of the 17th and 18th centuries. The multiplication of art See also:periodicals, lectures, books, photo-graphs, meetings of See also:societies and See also:gilds, museums, schools of arts and crafts, polytechnics, scholarships, facilities for travel, exhibitions, even those of the Royal See also:Academy, to which objects of applied art are now admitted, not only encourages many persons to become workers and designers in the applied arts, but exposes everything to the plagiarist, who travesties the freshest idea before it has well left the hands of its originator. Thus the inspirations of See also:genius, appropriated by those who imperfectly appreciate their subtle beauty and quality, become hackneyed and lose their See also:charm and interest. The keen See also:desire to be unconventional in applied art has spread from Great Britain and the United States to Germany, See also:Austria and other countries, but without well-defined first principles, or limitations. It seems agreed in a general way that the completed work in metal is to be wholly the conception and, as far as possible, the actual handiwork of the designer: casting by the See also:tire-perdue process, left practically untouched from the mould, and See also:embossing, being the two most favoured processes. The female figure is largely made use of, and rich and harmonious colours are sought, the glitter of metal being invariably subdued by deadening its lustre, or by patinas and oxides. Gilding, stains and lacquers, electro-plating, See also:chasing, " See also:matting," frosting, burnishing, mechanically produced See also:mouldings and enrichments, and the other processes esteemed in the loth century, are disused and avoided. New contrasts are formed by the juxtaposition of differently toned metals; or these with an inlay of haliotis See also:shell, introduced by Alfred Gilbert; or of coloured wax, favoured by Onslow Ford; or enamelling, perfected by Professor von Herkomer; or stained ivory, pearls, or semi-precious stones.

The quality of the surface left by the skilled artist or See also:

artisan is more regarded than symmetry of design, or even than correct modelling. Frequently only the important parts in a design are carefully finished and the rest merely sketched: the mode of working, whether by modelling-tools or hammer, being always left apparent. The newer kinds of art metal-work have, until recently, reached the purchaser direct from the producer's workshop; but they may now also be seen in the shops of silversmiths, jewellers, and general dealers, who are thus helping to See also:transfer production from large commercial manufactories to smaller ateliers under artistic control. The production of the larger household accessories, such as bedsteads, fenders, gas and electric fittings, docks, &c., has hardly as yet come under the influence of the art movement. The services rendered by Mr W. A. S. See also:Benson of See also:Chiswick, who commenced about 1886 to revolutionize the production of sheet-brass and copper utensils, cannot be passed over. The average ecclesiastical Platers' Work (see See also:BOILER) is distinguished from work in sheet metals by the fact that plates have considerable thickness, which sheets have not. Plates range in thickness from 4 in. to 2 in., but for most purposes they do not go beyond a in. or i in. Over these thicknesses they are used chiefly for the largest marine boilers, Armour plates which are several inches in thickness do not come in this group, being a special article of manufacture. Sheets are of thicknesses of less than } in.

This distinction of thickness is of importance in its bearing on workshop practice. A thin sheet requires a very different kind of treatment from a thick plate. Not only is more powerful machinery required for the latter, but in bending it allowance has to be made for the difference in See also:

radius of outer and inner layers, which increases with increase of thickness. Short, See also:sharp bends which are readily made in thin sheets cannot be done in thick plates, as the metal would be stressed too much in the outer layers. The methods of See also:union also differ, riveting being adopted for thick plates, and soldering or brazing generally for thin. Coppersmiths' Work is an important section of sheet-metal working. It is divided into two great departments: the domestic utensil side, on which the See also:brazier's craft is exercised; and the See also:engineering side, which is concerned in some See also:engine-work, See also:locomotive and marine, and in the manufacture of brewers' utensils. The methods of the first are allied to those of the tinman, those of the second to the methods of the plater. Tinsmiths' work resembles the lighter part of the work of the coppersmith. There is no essential difference in dealing with tin (i.e. sheets of iron or steel coated with tin) and copper of the same thickness. Hence the craft of tinmen and braziers is carried on by the same individuals. There are, however, See also:differences of treatment in detail, because copper is more malleable and softer than tin plate.

The See also:

geometry of sheet-metal work and of platers' and boiler-makers' work is identical up to a certain stage. The divergence appears when plates are substituted for sheets. A thin sheet has for all practical purposes no thickness—that is, the geometrical pattern marked on it will develop the object required after it is See also:bent. Nearly all patterns are the developments of the envelopes of geometrical solids of See also:regular or irregular outlines, few of See also:plane faces; when they are made up of combinations of plane faces, or of faces curved in one plane only, there is no difference in dealing with thin sheets or thick plates. But when curving occurs In different planes at right or other angles (hollowing), the metal has to be drawn or extended on the outside, and important differences arise. A typical form is the hemisphere, from which many modified forms are derived. The production of this is always a tedious task. It involves details of " wrinkling " and " razing," if done by hand-work in copper. In thick plates it is not attempted by hand, but pressing is done between See also:dies, or segments of the See also:sphere are prepared separately and riveted together. In tin it is effected by stamping. In all work done in thick plates the dimensions marked out must have reference to the final shape of the article. Generally and to See also:Russia, where, having little artistic past to refer to, the dimensions are taken as in the middle of the plate, but they may designers and craftsmen display unequalled individuality and force.

It is from the Far East, however, that the most serious rivalry may be anticipated. The metal-work of See also:

China and See also:Japan, so pleasantly naive and inexpensive, though becoming undesirably modified as to design through contact with See also:European buyers, is losing none of its matchless technique, which indeed in Japan is still being See also:developed. In any history of the art revival the influence of such firms as Barbedienne and Christofle in Paris and See also:Tiffany in New See also:York cannot be ignored. (J. S. G.) See also:Industrial Metal-Work. be on the inside or outside according to circumstances. But In any case the thickness must enter into the calculations, whereas in thin sheets no account is taken of thickness. Raised Work.—All the works in sheet metal that are bent in one plane only are easily made. The shapes of all polygonal and all cylindrical and conical forms are obtained by simple development—that is, the envelopments of these bodies are marked out on a flat plane, and when cut, are bent or folded to give the required envelopes. Only common geometrical problems are involved in the case of sheets of sensible thickness, and allowances are made for thickness. But in those forms where curving must take place in different directions the layers or See also:fibres of metal are made to glide over one another, extension taking place in some layers but not in others, and this goes on without producing much reduction in the thickness.

This is only possible with malleable and ductile metals and alloys. As a general rule it is restricted to metals which are not cast, for, with some sligkt exceptions, it is impossible to produce relative movements of the layers in cast iron, steel or cast brass. But most rolled metals and alloys can be so treated, copper being the best for the purpose. The methods employed are " raising " by the hammer, and pressing in dies. But the severity of the treatment would See also:

tear the material' asunder if rearrangement of the particles were not obtained by frequent annealing (q.v.). If an object has to be beaten into See also:concave form from a flat thin sheet, the outer portions must be hammered until they occupy smaller dimensions than on the flat sheet. If a circular disk is wrought into a hemisphere and the attempt is made to hammer the edges round, crumpling must occur. This in fact is the first operation, termed wrinkling, the edge showing a series of flutes. These flutes have to be obliterated by another series of hammerings termed razing. The result is that the object assumes a smooth concave and See also:convex shape, without the thickness of the metal becoming reduced. Cast Work.—The metals and alloys which are neither malleable nor ductile can only be worked into required shapes by melting and casting in moulds. Abundance of remains which date from the See also:Neolithic period testify to the high antiquity of this class of work, and also to the great skill which the ancient founders had, acquired.

Statue-founding is a highly specialized department of metal-work, in which the artists of the middle ages excelled. Two methods have been employed, the tire-perdue, or wax process (see above), and the present, or all sand method. In the latter the artist provides a See also:

model in See also:plaster from which the founder takes a mould within an encircling See also:box. This mould must obviously be made in scores of little separate sections (false cores or drawbacks) to permit of their removal from the model without causing fracture of the sand. These are subsequently replaced piece by piece in the encircling frame, and a core made within it, leaving a space of i in. or thereabouts into which the metal is poured. The advantage of this process is that the artist's model is not destroyed as in the Fire-perdue, and if a " waster " results, a second mould can be taken. A large statue occupies from one to three months in the moulding. The extreme tenuity of objects which are hammered, drawn or tolled cannot for obvious reasons be attained by casting. Casting also is complicated by the shrinkage which occurs in cooling down from the molten state, and in some alloys by the formation of eutectics, and the liquation of some constituents. The temperature of pouring is now known to be of more importance than was formerly suspected. The after-treatment of castings by annealing exercises great influence on results in malleable cast iron and steel. There are many metals and alloys which are malleable and ductile, and also readily fused and cast.

This is the case with gold, silver, copper, tin, lead and others, and especially with low carbon steel, which is first cast as an See also:

ingot, then annealed and rolled into plates as well as the thinnest sheets. The ancient wootz, and the products of the native furnaces of See also:Africa are first cast, then hammered out thin. Many of the patent bronzes are by slight See also:variations in the proportions of the constituents made suitable for casting, for See also:forging, and for See also:rolling into sheets. But in all the great modern manufacturing processes it is true that metals and alloys, though of the same name, have a different composition according as they are intended for casting on the one hand, or for forging, rolling and drawing on the other. Wrought or malleable iron has less of carbon and other elements in its composition than has cast iron. Steel intended for castings has slightly more carbon and other elements than the cast-steel ingot intended for rolling into plates. 'So also's. with the numerous bronzes, the phosphor, the See also:delta, the See also:aluminium and other alloys of copper; each is made in several grades to render it suitable for different kinds of treatment. , There are no materials used in manufacture of which the crafts-man is able to vary the composition and physical qualities so extensively as the metals and their alloys. Much light has been thrown on facts which have long been known in a practical way, by the labours of the Alloys Research See also:Committee of the Institution of Mechanical Engineers (England). These, together with See also:independent researches into the heat treatment of steel and iron, have opened up many unsolved problems fraught with deepest interest and importance. One of the most difficult problems with which the metal-worker 214 METAL-WORK who handles constructional forms has to deal is the See also:maintenance of a due relation between See also:absolute strength and a useful degree of elasticity. Only after many failures has the fact been grasped that a very high degree of strength is inconsistent with a trustworthy degree of elasticity.

The reasons were not understood until the researches of See also:

Wohler demonstrated the difference between the effects of merely dead loads and of live loads, and between repetitions of stress of one kind only, and the vastly more destructive effects of both kinds alternating. The texture of metals and alloys is related to the character of the operations which can be done upon them. Broadly the malleable and ductile metals and alloys show a fibrous character when ruptured, the fusible ones a crystalline fracture. The difference is seen both in the workshop and in the specimens ruptured in testing-See also:machines. A piece of wrought iron, or mild steel or copper, if torn asunder shows long lustrous fibres, resembling a bundle of threads in appearance. A piece of cast iron, or steel or bronze, shows on rupture a granular, crystalline surface destitute of any fibre. The ductile metals and alloys also extend from 10 to 30 % with reduction of See also:area before they fracture, the crystalline ones snap shortly without warning. In some instances, however, the method of application of stress exercises an influence. Wrought iron and mild steel may be made to show a short and crystalline fracture by a sudden application of stress, while if drawn asunder slowly they develop the silky, fibrous appearance. The men who design and work in metals have to take account of these vital differences and characteristics, and must be careful not to apply treatment suitable to one kind to another of a dissimilar character. Tools, appliances and methods have little in common. Between the work of the smith, the sheet-metal worker and the founder, there is a great gulf.

An artistic taste will recognize the essential differences, and not endeavour, apart from questions of strength, to See also:

graft a design suitable for one on another. It is bad taste to imitate the tracery of the ductile wrought iron in cast designs, the foliations of ancient wrought-iron grilles and screens in heavy cast iron. Severe simplicity is also most in See also:harmony with constructional designs in plated work, where stresses occur in straight lines. From this point of view the lattice-girder See also:bridge is an ideal design in steel. One of the most valuable characteristics of the - iron alloys is their capacity for hardening, which they owe in the main to the presence of certain small percentages of carbon relatively to minute quantities of other elements: as manganese, See also:tungsten, nickel and others of less importance. The capacity for hardening is an in-valuable See also:property not only in regard to cutting-tools, but also in prolonging the life of parts subjected to severe friction. Great advances have been made in the utilization of this property as a result of the growth of the precision grinding-machines, which are able to correct the inaccuracies of hardened work as effectually as those of soft materials. It is utilized in the spindles of machine-tools, in the balls and rollers for high-speed See also:bearings, slides, pivots and such like. Methods of Union.—The methods of union of works in metal are extremely varied. An advantage in casting is that the most complicated shapes are made in one piece. But all other complicated forms have to be united by other means—as welding, soldering, riveting or bolting. The two first-named are trustworthy, but are evidently unsuitable for the greater portion of engineers' work, for which riveting and bolting are the methods adopted.

Even the simple elements of rivets and bolts have produced immense developments since the days when bolts were made by hand, holes cored or hand-drilled, and rivets formed and closed by hand labour. See also:

Nut- and See also:bolt-making machinery, both for forging and See also:screw cutting, operates automatically, and drilling machinery is highly specialized. Hand-riveting on large contracts has been wholly displaced by power-riveting machines. The methods of union adopted are. not allowed to impair the strength of structures, which is calculated on the weakest sections through the See also:rivet or bolt holes. Hence much ingenuity is exercised in order to obtain the strongest See also:joint which is consistent with See also:security of union. This is the explanation of all the varied forms of riveted See also:joints, which to casual observers often appear to be of a fanciful character. See also:Protection of Surfaces.—The protection and coloration of metals and alloys includes a large number of industries. The engineer uses paints for his iron and steel. A small amount of work is treated by the See also:Bower-Barff and allied processes, by which a coating of magnetic oxide is left on the metal. Hot See also:tar—See also:Angus Smith's process—is used for water-pipes. Boiled See also:linseed-oil is employed as a non-corrosive coating preceding the application of the lead and iron oxide paints. In steam boilers artificial galvanic couples are often set up by the suspension of zinc plates in the boiler, so that the corrosion of the zinc may preserve the steel boiler, plates from waste.

Various artificial protective coatings are applied to the plates of steel See also:

ships. See also:Bright surfaces are protected with oil or with See also:lacquer. The ornamental bronzes and brasses are generally lacquered, though in engineers' machinery they are as a rule not protected with any coating. For ornamental work lacquering divides favour with colouring—sometimes done with coloured lacquers, but often with chemical colourings, of which the copp er and iron salts are the chief basis. (J. G.

End of Article: METALLOGRAPHY

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