Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 2, 1802).djvu/55

Rh by mixing red and yellow colours together in due proportions.

5. .—The chief colours of this kind are, Kings and Naples-yellow, Dutch-pink, and Turbith-mineral.

Kings-yellow is prepared from arsenic. Its colour is very beautiful, but apt to fade, on which account, as well as from its great price, it is but seldom employed.

The basis of Naples-yellow is lead: it therefore frequently turns black; is particularly liable to be spoiled by iron, when moist, and should never come in contact with that metal, unless previously ground in oil.

Dutch-pink is said to be prepared by striking the colour of yellow berries upon chalk finely levigated. This, however, we doubt much, as its basis is harder and more gritty than chalk, and its colour more durable than others prepared in a similar manner.

 is, at present, but little used in painting, though it appears to be very durable, and is therefore preferable both to Kings and Naples-yellow.

6. . The only simple green of a tolerable degree of brightness, is , or its different preparations: though far from being durable, it may be rendered more so, as a water-colour, by dissolving it in the pure tartarous acid.—A green colour may be made by compounding Prussian, or other blue, with yellow; but it is by no means fixed, and much inferior to common verdigrease.

7. . The principal blue colours are, Prussian and Dutch Blue, Verditer, Smalt, Bice, and Indigo.

Various processes have been adopted for the making of Prussian-blue, of which we shall select the shortest.

Take 3lbs. of dried ox's blood, 4lbs. 8oz. of quick-lime, 2lbs. of red tartar, and 1lb. 8oz. of saltpetre. Let them be calcined and lixiviated, when the lye should be poured into a solution of 4lbs. of alum, and 1lb. of green vitriol. This operation will produce the finest blue; but the quantity will exceed little more than 8oz. and 4 drams.

Dutch-blue. See, vol. i. p. 296.

The preparation of  is studiously concealed, so that the best chemists of Europe have been baffled in discovering its component parts. It is very bright, and has a considerable tinge of green. This colour is durable in water; but, like verdigrease, dissolves in oil, and is subject to the same inconveniencies.

 is glass coloured with zaffre; a preparation from cobalt. It is, in general, so grossly pulverized as to be unfit for painting, and its texture is so hard, that it cannot easily be levigated. Its colour is exceedingly bright and durable; and, if finely pulverized, is little inferior to Prussian-blue.

Bice is prepared from the Lapis Armenus, a stone which was formerly brought from Armenia, but now from Germany. Bice bears the best body of all bright blues in common use, but it is the palest in colour. Being somewhat sandy, it is necessary to grind it very fine, and to wash it well, previously to its being used. It is as durable, and yields nearly as good a colour, as Prussian-blue.

Indigo is but little employed in painting, either in oil, or water, on account of the dullness of the