Chalk1

In use for at least the last 50,000 years it is one of the rst pigments used by mankind. Readily available and easy to grind into a powder it had no challenger until the invention of the lead whites in Ancient Greece.

Composed of the fossilised microscopic remains of phytoplankton algae, chalks often develop as very thick and extensive deposits, the most famous being the cliffs of the English southern coast. The chalk sample shown here is from chalk pits in the Chiltern hills of England.

Chalk, in its many guises; English whiting, Bologna chalk or Champagne chalk, has, since the early Renaissance, been used to make a traditional ‘gesso’ ground. A mixture of chalk and animal glue made from the hides or bones of rabbits it makes a bright white, smooth plaster surface that was applied to timber panels prior to application of egg tempera paint.

With the adoption of oil painting in the 15th century, chalk lost its importance as a white pigment as it will turn almost transparent when added to linseed oil.

Since then it has been used mostly as an extender for other pigments and as the bulk content of soft pastels.

Because it is simple calcium carbonate it can be cheaply manufactured arti cially and the majority of ‘chalk’ sold today for use in industrial application is not the natural variety.