Chalkboard

From Free net encyclopedia

This article is about chalkboards. For other meanings, see (disambiguation).

Image:Chalkboard.jpg Image:Tafelkreide1.jpg

A chalkboard or blackboard (and similar colour based names for the same thing) is a reusable writing surface on which text or drawings are made with chalk or other erasable markers. Chalkboards were originally made of smooth, thin sheets of black or dark grey slate stone.

A chalkboard can simply be a piece of board painted with matte dark paint (usually dark green or black). It is usually dark green as this is less harsh on the eyes than black. 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.

Chalkboards are commonly used in teaching. The chalk marks can be quickly and easily wiped off with a damp cloth, or a special blackboard eraser consisting of a block of wood covered by a felt pad. Chalkmarks made on some types of wet chalkboard can be difficult to remove.

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

Chalkboards 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. However, other methods of displaying information are more expensive and have drawbacks of their own. These disadvantages have led to the widespread adoption of the whiteboard, which uses ink markers that produce no dust.

The scratching of fingernails on a chalkboard is a sound that is well-known for being extremely irritating.de:Schreibtafel nl:Schoolbord pt:Quadro negro simple:Blackboard sv:Svarta tavlan th:กระดานดำ zh:黑板