Blackboard chalk

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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

Sources Checked for Data in Record

  • Encyclopedia Britannica, http://www.britannica.com Comment: crayon." Encyclop√¶dia Britannica. 2005. Encyclop√¶dia Britannica Premium Service 10 Mar. 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

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