ZINC WHITE

First introduced in 1840, this white is colder in appearance than lead white, and doesn't cover nearly as well, yet it is far less expensive. It is also non-poisonous, is permanent and doesn't yellow, though all these positive factors are true only with pure zinc white, as something less chemically pure, evidently will prove. If you heat zinc white, it turns to lemon yellow, but will revert to white when cooled. It differs from lead white in this respect. It also disintegrates quickly out of doors, increases in volume thus causing massive crackling, so it is not useful in fresco at all. Ground in oil it dries slowly, especially in poppy oil, where the retarded drying time is needed. It does not dry as solid as lead white, due to some transparency in the pigment. A small addition of damar or mastic varnish speeds up the drying time. As it is very fine in powder form, it can be sufficiently mixed with only a spatula, requiring 30% oil and an addition of 2% wax in the tube to prevent hardening. It is compatible with all other pigments, including copper based, but in watercolor it is destructive to the permanency of coal-tar colors and accelerates the process of fading (though it definitely doesn't do this in oil.)

ZINC YELLOW

Zinc chromate is a slightly poisonous, light lemon-colored pigment, which is obtainable only in this one tone, although richer tones can be produced without difficulty. It requires 40% oil, dries well, but fatally turns green when used pure as an oil color. It is not absolutely waterproof; the powder partially dissolves when shaken with water, and if moisture condenses on the surface, a yellow sheen will spread over the affected parts. In fresco, it can dissolve from the spot it is applied to, and reappear nearby where it has longer remained wet. Because of its tendency to turn green, it should not be used in sensitive areas such as atmospheric tones. When mixed with chrome oxide, permanent green, as a half tone, it is very useful.