Pigments through the Ages - Manufacture Recipes

How Emerald green is made:

Artificial variety of pigment	Reaction of sodium arsenite with copper(II)-acetate.

19th century recipe	Dissolve in a small quantity of hot water, 6 parts of sulphate of copper; in another part, boil 6 parts of oxide of arsenic with 8 parts of potash, until it throws out no more carbonic acid; mix by degrees this hot solution with the first, agitating continually until the effervescence has entirely ceased; these then form a precipitate of a dirty greenish yellow, very abundant; add to it about 3 parts of acetic acid, or such a quantity that there may be a slight excess perceptible to the smell after the mixture; by degrees the precipitate diminishes the bulk, and in a few hours there deposes spontaneously at the bottom of the liquor entirely discolored, a powder of a contexture slightly crystalline, and of a very beautiful green; afterwards the floating liquor is separated.