This pigment is used extensively- it is almost transparent in oil but it gives opacity to watercolor and is used in gouache. Can be limestone or marble. In painting literature it is also sometimes called whiting. This can also include marble dust, which comes in several very different particle sizes.

Sometimes chalk is used as a base, and it is commonly used as an extender in oil paint. Unfortunately its use in titanium white can accelerate some forms of degradation, though this seems to happen to a lesser extent with chalk than it does with barium sulfate, another common extender. A fuller discussion of that study can be found in this article which was shared by George O’Hanlon. While this color has an excellent blue wool scale rating, its role in lightfastness is still being explored.

Monona Rossol mentions in her work to use the standards for nuisance dusts if working with chalk.

It is available in several grades of coarseness or fineness.

Sometimes PW18:1 Dolomite (with some magnesium carbonate) can be an impurity in chalk.