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ULTRAMARINE

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Originally appearing in Volume V27, Page 570 of the 1911 Encyclopedia Britannica.
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ULTRAMARINE , a See also:

blue pigment, consisting essentially of a See also:double silicate of See also:aluminium and See also:sodium with some sulphides or sulphates, and occurring in nature as a proximate component of lapis lazuli (q.v.). As See also:early at least as the Irth See also:century the See also:art of extracting a blue pigment from lapis lazuli was practised, and from the beginning of the 16th century this pigment began to be imported into See also:Europe from " over the See also:sea," as azurrum ultramarinum. As the See also:mineral only yields from 2 to 3% of the pigment, it is not surprising to learn that the pigment used to be weighed up with See also:gold. It was valued chiefly on See also:account of its brilliancy of See also:tone and its inertness in opposition to sunlight, oil, and slaked See also:lime (in See also:fresco-See also:painting). In 1814 Tassaert observed the spontaneous formation of a blue See also:compound, very similar to ultramarine, if not identical with it, in a soda-See also:furnace at St Gobain, which caused the Societe pour l'Encouragement d'Industrie to offer, in 1824, a See also:prize for the artificial See also:production of the See also:precious See also:colour. Processes were devised by See also:Guimet (1826) and by See also:Christian See also:Gmelin (1828), then See also:professor of See also:chemistry in See also:Tubingen; but while Guimet kept his See also:process a See also:secret Gmelin published his, and thus became the originator of the " artificial ultramarine " See also:industry. The details of the commercial processes are See also:trade secrets. The raw materials used in the manufacture are: (I) See also:iron-See also:free See also:kaolin, or some other See also:kind of pure See also:clay, which should contain its See also:silica and alumina as nearly as possible in the proportion of 2SiO2 : Al20, demanded by the See also:formula assigned to ideal kaolin (a deficit of silica, however, it appears can be made up for by addition of the calculated See also:weight of finely divided silica); (2) anhydrous sulphate of soda; (3) anhydrous carbonate of soda; (4) See also:sulphur (in the See also:state of See also:powder) ; and (5) powdered See also:charcoal or relatively ash-free See also:coal, or colophony in lumps. " Ultramarine poor in silica " is obtained by fusing a mixture of soft clay, sodium sulphate, charcoal, soda and sulphur. The product is at first See also:white, but soon turns See also:green (" green ultra-marine ") when it is mixed with sulphur and heated. The sulphur fires, and a See also:fine blue pigment is obtained. " Ultramarine See also:rich in silica " is generally obtained by See also:heating a mixture of pure clay, very fine white See also:sand, sulphur and charcoal in a muffle-furnace.

A blue product is obtained at once, but a red tinge often results. The different ultramarines—green, blue, red and See also:

violet—are finely ground and washed with See also:water. Artificial, like natural, ultramarine has a magnificent blue colour, which is not affected by See also:light nor by contact with oil or lime as used in painting. Hydrochloric See also:acid at once bleaches it with liberation of sulphuretted See also:hydrogen and See also:milk of sulphur. It is remarkable that even a small addition of See also:zinc-white (See also:oxide of zinc) to the reddish varieties especially causes a considerable diminution in the intensity of the colour, while dilution with artificial precipitated sulphate of lime (" annalin ") or sulphate of baryta (" See also:blanc See also:fix ") acts See also:pretty much as one would expect. Ultramarine being very cheap, it is largely used for See also:wall painting, the See also:printing of paperhangings and See also:calico, &c., and also as a corrective for the yellowish tinge often See also:present in things meant to be white, such as See also:linen, See also:paper, &c. Large quantities are used in the manufacture of paper, and especially for producing that kind of See also:pale blue See also:writing paper which is so popular in See also:Great See also:Britain. The See also:composition of the pigment is quite similar to that of lapis lazuli; but the constitution of both is uncertain. By treating blue ultramarine with See also:silver nitrate See also:solution, " silver-ultramarine " is obtained as a yellow powder. This compound gives a blue See also:potassium- and See also:lithium-ultramarine when treated with the corresponding chloride, and an See also:ethyl-ultramarine when treated with ethyl icdide. See also:Selenium- and See also:tellurium-ultramarine, in which these elements replace the sulphur, have also been prepared. It has been suggested that ultramarine is a compound of a sodium aluminium silicate and sodium sulphide.

Another view is that the colour is due to some comparatively See also:

simple substance suspended in a colourless See also:medium.

End of Article: ULTRAMARINE

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