Pumice

Pumice is a lightweight stone produced in volcanos. Ground finely it becomes a sand-like gritty substance that is used by artists for very toothy grounds, and for adding texture to paint. This may be for simple visual effect or to provide a rough tooth for the application of pastels and other dry media. Some artists mix it with acrylic medium or paint, depending on the effect required and then paint it onto paper, board or canvas. In this form it has enough tooth to hold pastel with a minimum of, or zero, fixative. Pumice stone has also been known to be used with one flat side as an effective sanding and smoothing tool for preparing painting surfaces or when working sculpture and was commonly used this way before the development of modern sandpapers.