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ENGRAVING OF COPPER

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Originally appearing in Volume V26, Page 698 of the 1911 Encyclopedia Britannica.
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ENGRAVING OF See also:COPPER ROLLERS The engraving of copper rollers is one of the most important branches of textile-See also:printing and on its perfection of See also:execution depends, in See also:great measure, the ultimate success of the designs. Roughly speaking, the operation of engraving is performed by three different methods, viz. (1) By See also:hand with a graver which cuts the See also:metal away; (2) by See also:etching, in which the See also:pattern is dissolved out in nitric See also:acid; and (3) by See also:machine, in which the pattern is simply indented. (I) Engraving by hand is the See also:oldest and most obvious method of engraving, but is the least used at the See also:present See also:time on See also:account of its slowness. The See also:design is transferred to the See also:roller from an oil-See also:colour tracing and then merely cut out with a See also:steel graver, prismatic in See also:section, and sharpened to a bevelled point. It requires great steadiness of hand and See also:eye, and although capable of yielding the finest results it is only now employed for very See also:special See also:work and for those patterns which are too large in See also:scale to be engraved by See also:mechanical means. (2) In the etching See also:process an enlarged See also:image of the design is See also:cast upon a See also:zinc See also:plate by means of an enlarging See also:camera and prisms or reflectors. On this plate it is then painted in See also:colours roughly approximating to those in the See also:original, and the outlines of each colour are carefully engraved in duplicate by hand. The See also:necessity for this is that in subsequent operations the design has to be again reduced to its original See also:size and, if the outlines on the zinc plate were too small at first, they would be impracticable either to etch or See also:print. The reduction of the design and its See also:transfer to a varnished copper roller are both effected at one and the same operation in the See also:pantograph machine. This machine is capable of reducing a pattern on the zinc plate from one-See also:half to one-tenth of its size, and is so arranged that when its pointer or " stylus " is moved along the engraved lines of the plate a See also:series of See also:diamond points cut a reduced facsimile of them through the See also:varnish with which the roller is covered. These diamond points vary in number according to the number of times the pattern is required to repeat along the length of the roller.

Each colour of a design is transferred in this way to a See also:

separate roller. The roller is then placed in a shallow trough containing nitric acid, which acts only on those parts of it from which the varnish has been scraped. To ensure evenness the roller is revolved during the whole time of its See also:immersion in the acid. When the etching is sufficiently deep the roller is washed, the varnish dissolved off, any parts not quite perfect being retouched by hand. (3) In machine engraving the pattern is impressed in the roller by a small cylindrical " See also:mill " on which the pattern is in See also:relief. It is an indirect process and requires the utmost care at every See also:stage. The pattern or design is first altered in size to repeat evenly See also:round the roller. One repeat of this pattern is then engraved by hand on a small highly polished soft steel roller, usually about 3 in. See also:long and 4 in. to 3 in. in See also:diameter; the size varies according to the size of the " repeat " with which it must be identical. It is then re-polished, painted with a chalky mixture to prevent its See also:surface oxidizing and exposed to a red-See also:heat in a See also:box filled with See also:chalk and See also:charcoal; then it is plunged in See also:cold See also:water to harden it and finally tempered to the proper degree of toughness. In this See also:state it forms the " See also:die " from which the " mill " is made. To produce the actual " mill " with the design in relief a softened steel See also:cylinder is screwed tightly against the hardened die and the two are rotated under constantly increasing pressure until the softened cylinder or " mill " has received an exact replica in relief of the engraved pattern. The " mill " in turn is then hardened and tempered, when it is ready for use.

In size it may be either exactly like the " die " or its circumferential measurement may be any multiple of that of the latter according to circumstances. The copper roller must in like manner have a circumference equal to an exact multiple of that of the " mill," so that the pattern will join up perfectly without the slightest break in See also:

line. The modus operandi of engraving is as follows:—The " mill " is placed in contact with one end of the copper roller, and being mounted on a See also:lever support as much pressure as required can be put upon it by adding weights. Roller and " mill " are now revolved together, during which operation the See also:projection parts of the latter are forced into the softer substance of the roller, thus engraving it, in See also:intaglio, with several replicas of what was cut on the original " die." When the full circumference of the roller is engraved, the " mill " is moved sideways along the length of the roller to its next position, and the process is repeated until the whole roller is fully engraved.

End of Article: ENGRAVING OF COPPER

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