Blackboard chalk

Description

A soft, chalky stick used to write on blackboards by students and teachers since the early 1800s. Blackboard chalk originally contained calcium carbonate typically bound with kaolin clay, oleic acid, and sodium hydroxide. A wide variety of formulations are now used, most of which are made from calcium sulfate hemihydrate (plaster of Paris), which reacts with water to form gypsum. Dry pigments may be added for increased whiteness or coloration.

Synonyms and Related Terms

blackboard crayon

Authority

• Encyclopedia Britannica, http://www.britannica.com Comment: crayon." Encyclopædia Britannica. 2005. Encyclopædia Britannica Premium Service 10 Mar. 2005 .

• Website address 1 Comment: Answers.com at http://www.answers.com/topic/chalk

• Website address 2 Comment: wikipedia: http://en.wikipedia.org/wiki/Chalk access March 10, 2005

• The Dictionary of Art, Grove's Dictionaries Inc., New York, 1996 Comment: "Crayon"

• External source or communication Comment: Submitted information: David Kearny, Conservator of Painted Surfaces, Australian War Memorial, Mar. 2005