Chalkboard

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This article is about the writing surface. For other uses, see Chalkboard (disambiguation).

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Writing teacher

A chalkboard, with multiple colors of chalk

A quadruple chalkboard at the Helsinki University of Technology

Portable blackboard in a mind-reading performance, 1900

Blackboard eraser.

A cleaner for a blackboard eraser.

A chalkboard or blackboard is a reusable writing surface on which text or drawings are made with chalk or other erasable markers.^[specify] Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone.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.

A blackboard 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 enameled 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.

In the past, blackboards were commonly used in teaching. The chalk marks could be easily wiped off with a damp cloth or a special blackboard eraser consisting of a block of wood covered by a felt pad. However chalkmarks made on some types of wet blackboard could be difficult to remove. Blackboard manufacturers often advised 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.

Sticks of processed "chalk" were produced especially for use with blackboards in white and also in various colours. These were not actually made from chalk rock but from gypsum.

Blackboards have disadvantages: they produce a fair amount of dust, 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. However, these alternative methods of displaying information have drawbacks of their own.

The scratching of fingernails on a blackboard is a sound that is well-known for being extremely irritating.

Blackboards are also used in many establishments (typically public houses) as a form of advertising often for upcoming events and menus - as well as to keep the score in darts matches.