3. Dissolve acetate of lead in warm water, and add of sulphuric acid, q. s. to convert it into sulphate of lead; decant the clear liquid (vinegar), wash the residuum with soft water, and digest it, with agitation, in a hot solution of neutral (yellow) chromate of potash, containing 1 part of that salt to every three parts of sulphate of lead operated on; afterwards decant the liquid, which is a solution of sulphate of potash, and carefully drain, wash, and dry the newly formed pigment. The product contains much sulphate of lead, but covers as well, and has as good a colour, as pure chromate of lead, whilst it is much cheaper. The shade may be varied by increasing or lessening the quantity of the chromate.[273]
[273] Armengaud’s ‘Génie Industriel,’ April, 1853.
Obs. Four shades of this beautiful pigment are met with in the shops, viz. pale yellow or straw colour, yellow, deep yellow, and orange. The former are made by adding a little alum or sulphuric acid to the solution of the chromate before mixing it with the solution of lead; the last, by the addition of a little subacetate of lead (tribasic acetate), or by washing the precipitate with a weak alkaline lye. The darker colour appears to arise from a little ‘dichromate’ being thrown down intimately mixed with the neutral chromate, and the paler shades from a slight excess of acid, or from the presence of water-sulphate of lead, and, occasionally, alumina. The colour is also influenced by the temperature of the solutions at the time of admixture. Anthon has found that, when hot solutions of equal equivalents of acetate of lead (190 parts) and chromate of potash (100 parts, both neutral and in crystals) are mixed, the yellow precipitate, when dried, is anhydrous; but when the mixture is made at ordinary temperatures, the precipitate has a paler yellow, and when dried contains 1 eq., or nearly 51⁄4% of water. (‘Buch. Rept.’) It thus appears that the shades of colour of chrome yellow may be varied, without any foreign addition. In practice, the third formula will be found very satisfactory. See Orange Chrome and Chrome Red.
Dutch Pink. Prep. Take of French berries, 1 lb.; turmeric, 1⁄2 lb.; alum, 1⁄2 lb.; water, 11⁄2 gall.; boil 1⁄2 an hour, strain, evaporate to 2 quarts, adding of whiting, 3 lbs., and dry by a gentle heat. Starch, or white lead, is sometimes employed instead of whiting, to give it a body. Golden yellow. Used as a pigment; but will not glaze like brown pink.
English Pink. Syn. Light pink. As the last, but using 5 lbs. of whiting.
Indian Yellow. See Purree.
King’s Yellow. Factitious tersulphuret of arsenic.
Naples Yellow. Syn. Mineral yellow. Prep. 1. Take of metallic antimony, in powder, 3 lbs.; red lead, 2 lbs.; oxide of zinc, 1 lb.; mix, calcine, well triturate the calx, and fuse it in a covered crucible; the fused mass must be reduced to an impalpable powder by grinding and elutriation.
2. Flake white, 11⁄2 lb.; diaphoretic antimony, 1⁄4 lb.; calcined alum, 1 oz.; sal ammoniac, 2 oz.; calcine in a covered crucible with a moderate heat for 3 hours, so that at the end it may be barely red hot. More antimony and sal ammoniac turn it on the gold colour.
3. (Guimel.) Washed diaphoretic antimony, 1 part; pure red lead, 2 parts; grind them to a paste with water, and expose this mixture to a moderate red heat for 4 or 5 hours, as before. Used in oil, porcelain, and enamel painting. Chrome has now nearly superseded it for ordinary purposes.