Yellows (1): Sulphate of copper and salammoniac, equal parts, dissolved in water; (2) onion-juice; both visible on heating Black (1): Weak infusion of galls. This is turned black by weak solution of protosulphate of iron. (2) Weak solution of protosulphate of iron. Turns blue when moistened by weak solution of prussiate of potash, and black by infusion of galls. Brown: Very weak solutions of nitric, sulphuric, muriatic acids, common salt, or nitrate of potash. Visible on heating. Green: Solution of nitro-muriate of cobalt. Brought out by heat; fades when cool. Rose-red: Acetate of cobalt solution, with a small quantity of nitrate of potash. Acts as preceding. Solutions of nitrate of silver and terchloride of gold become permanently dark when exposed to sunlight.