Blackboard chalk

Description

A soft, chalky stick used to write on blackboards by students and teachers since the early 1800s. Blackboard chalk originally contained carbonate calcium carbonate typically bound with kaolin clay, acid oleic acid, and hydroxide sodium hydroxide. A wide variety of formulations are now used, most of which are made from calcium sulfate hemihydrate (of Paris 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." Encyclopdia Britannica. 2005. Encyclopdia Britannica Premium Service 10 Mar. 2005 .

• Website address 1, 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, External source or communication Comment: Submitted information: David Kearny, Conservator of Painted Surfaces, Australian War Memorial, Mar. 2005