2688. Blue Verditer

2688.    Blue Verditer. It is generally stated to be made by adding chalk to a solution of nitrate of copper produced in the process of refining silver; but Mr. Phillips did not succeed in making it by this means, and found no lime in the best samples. This pigment is acted upon by suphurretted hydrogen; it should not be used in oil, and though more stable in water, it is hardly a pigment for high art work. Certain blues are made from the natural blue basic carbonate of copper, and from malachite, but they have no interest for the artist.

2689. New Blue

2689.    New Blue. Mix equal parts of common arseniate of copper (see Mineral Green, No. 2711), and neutral arseniate of potash, fuse by heat in a large crucible, then add to the fused salt 1/5 its weight of nitre. Effervescence takes place, and the salt becomes blue. Cool, pulverize, and wash.

2690. Cobalt Blue

2690.    Cobalt Blue. Th'enard's blue is made by precipitating a soluble cobalt salt with a solution of alum, and heating the precipitate. "When well made, it is a good permanent color, useful in oil and water. It can also be employed in fresco and silicious painting. It is, however, somewhat affected by light, losing its brilliancy slightly.

2691. Eisner's Preparation of Zinc Green

2691.    Eisner's Preparation of Zinc Green. Sprinkle with water a mixture of 5 parts oxide of zinc and 1 part of sulphate of cobalt, dry the pulp thus obtained, then heat to redness. A deep green powder is obtained. If 10 parts oxide of zinc, and 1 part sulphate of cobalt be employed, the product is grass green in color; the same color, only lighter, is obtained when the latter proportion of zinc oxide is again doubled. These colors, especially the latter, may replace to advantage Schweinfurt green; they apply well on a coating of lime.

2692. Bistre

2692.     Bistre. This is a brown color which is used in water-color painting. It is prepared from the root of beech-wood by washing away the soluble parts with water.

The insoluble residue is mixed with gum water and formed into cakes.

2693. White Lead

2693.     White Lead. This pigment, which enters largely into the composition of various colored paints, is carbonate of lead, obtained by suspending rolls of thin sheet lead over malt vinegar or pyroligneous acid in close vessels, the evaporation of the acid being induced and sustained by the heat of a steam-bath or other appliances.

2694. Test for White Lead

2694.    Test for White Lead. Commercial carbonate of lead is never quite pure, being commonly adulterated with sulphate of baryta, (heavy spar), and sometimes with chalk. The former may be detected by its insolubility in dilute nitric acid, and the latter by the nitric solution yielding a white precipitate with oxalic or sulphuric acid, or oxalate of ammonia, after having been treated with sulphuretted hydrogen, or a hydrosulphuret, to throw down the lead. (Cooley.)