2706. Chrome Red

2706.      Chrome Red. Melt saltpetre in a crucible heated to dull redness, and add chrome yellow, by small portions, till no more red fumes arise. Allow the mixture to settle, then pour off the melted salt from the heavy sediment, and wash the latter with water, which should be quickly poured off, and dry the pigment. The liquefied salt poured off contains chromate of potash, and is reserved for making chrome yellow.

2707. Orange Chrome

2707.     Orange Chrome is chrome yellow acted on by an alkali, which deprives it of part of the chromic acid. All the chromes are chromates of lead, and are therefore liable to be blackened by sulphuretted hydrogen. When used with oil, they may, with care, retain their color for a long time, the oxidized oil protecting them from the action of sulphuretted hydrogen. They cannot be used in silicious, fresco, or any other method of water painting. They are destroyed by alkalies ; they should never be used with Prussian blue or kindred colors. On the whole, it would be as well for artists to reject them, as better and safer pigments can be employed for the same purpose as they are.

2708. Aureolin Yellow

2708.    Aureolin Yellow. An excellent pigment in every respect. It is a double nitrate of potassium and cobalt. It is not acted upon by lime or by potash; it is, therefore, a good pigment for fresco and silicious painting. It may be used with safety in oil and in water. Sulphuretted hydrogen does not affect it, and it is permanent when submitted to the severest tests. It is not affected by admixture with other colors.

2709. Naples Yellow

2709. Naples Yellow. Mix 12 parts metallic antimony, 8 parts red lead, and 4 oxide of zinc, and calcine in a reverberatory furnace. The mixed oxides are rubbed together, fused, and the fused mass elutriated into a fine powder. (Dr. Ure.) M. Guimel recommends 1 part well-washed antimoniate of potash to be ground into a paste with 2 parts red lead, and the powder exposed to a red heat for 4 or 5 hours, keeping the heat moderate. This is a good pigment, and may safely be used with oil.

2710. Brunswick Green

2710. Brunswick Green. Pour a saturated solution of muriate of ammonia over copper filings in a close vessel placed in a warm situation; add more of the solution from time to time till 3 parts of the muriate have been used to 2 of copper. After standing for a few weeks the pigment is separated from the unoxidized copper by washing through a sieve. It is then to be well washed, and dried slowly in the shade. It is often reduced with white lead; some samples contain arsenic.

2711. Mineral Green, Scheele's Green, or Arsenite of Copper

2711.  Mineral Green, Scheele's Green, or Arsenite of Copper. Dissolve 11 ounces white arsenic and 2 pounds carbonate of potash, by heat, in a gallon of water. Dissolve also 2 pounds sulphate of copper in 3 gallons water. Filter each solution separately, and add the former gradually to the latter as long as it occasions a precipitate. Wash the precipitate, drain it, and dry it.