Black Chalk Board

A chalkboard or blackboard is a reusable writing surface on which text or drawings are made with sticks of calcium sulphate, known, when used for this purpose, as chalk . Chalkboards were originally made of smooth, thin sheets of black or dark grey slate stone. Modern versions are often green or brown and are thus sometimes called a greenboard or brownboard instead.

Design

A chalkboard can simply be a piece of board painted with matte dark paint (usually black or dark green). A more modern variation consists of a coiled sheet of plastic drawn across two parallel rollers, which can be scrolled to create additional writing space while saving what has been written. The highest grade chalkboards are made of a rougher version porcelain enamelled steel (black, green, blue or sometimes other colours). Porcelain is very hard wearing and chalkboards made of porcelain usually last 10-20 years in intensive use.

The chalk marks can be easily wiped off with a damp cloth, a sponge or a special chalkboard eraser consisting of a block of wood covered by a felt pad. However, chalk marks made on some types of wet chalkboard can be difficult to remove. Chalkboard manufacturers often advise that a new or newly resurfaced chalkboard be completely covered using the side of a stick of chalk and then that chalk brushed off as normal to prepare it for use.

Chalk sticks

Sticks of processed "chalk" are produced especially for use with chalkboards in white and also in various colours. These are not actually made from chalk rock but from calcium sulfate in its dihydrate form, gypsum.

Uses

Chalkboards are often used in teaching, although in wealthier countries their use has diminished. Chalkboards are also used in many establishments (typically public houses) as a form of advertising often for upcoming events and menus and to record the score in darts matches. Also in homes specifically in the Kitchen, for writing messages, shopping lists and things to remember as well as sometimes serving a decorative purpose.

Drawbacks

Chalkboards have disadvantages: they produce dust, the amount depending on the quality of chalk used. Some people find this uncomfortable or may be allergic to it, and there has been speculation about links between chalk dust and respiratory problems. The dust also precludes the use of chalk in areas shared with dust-sensitive equipment such as computers.

The scratching of fingernails on a chalkboard, as well as other pointed, especially metal objects against chalkboards, produces a sound that is well-known for being extremely irritating. Many are averse also to merely the sight or thought of this sort of contact.

Etymology and history

The term "blackboard" dates from around 1815 to 1825 while the newer and predominantly American term, "chalkboard" dates from 1935 to 1940.

The chalkboard was introduced into the US education system in 1801.

Gallery

See also

• Chalkboard gag from The Simpsons
• Chalkzone
• Sidewalk chalk
• Sound of fingernails scraping chalkboard
• Whiteboard
• Interactive whiteboard
• Slate

References

1. ^ "Blackboard - Dictionary.com" . http://dictionary.reference.com/browse/blackboard .  
2. ^ "Chalkboard - Dictionary.com" . http://dictionary.reference.com/browse/chalkboard .  
3. ^ The Cato Education Market Index , http://cato.org/pubs/pas/pa585.pdf  

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