Chalkboard

From Wikipedia, the free encyclopedia

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

Image:Tafelkreide1.jpg Image:Math lecture at TKK.JPG

A chalkboard or blackboard (and similar colour based names) 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 Chalkboards were originally made of smooth, thin sheets of black or dark grey slate stone.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 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.

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. Chalkboard manufacturers often advise that a new or newly resurfaced chalkboard is 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" 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. These disadvantages have led to the widespread adoption of the whiteboard, which uses ink markers that produce no dust. However, other methods of displaying information are more expensive and have drawbacks of their own.

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

[edit] Terminology

The term "blackboard" was invented about 1820, while the newer term "chalkboard" was first coined in the 1930s.<ref>Dictionary.com Unabridged (v 1.0.1).</ref>. Some think that the term "chalkboard" is used rather than "blackboard" for reasons of political correctness.<ref>BBC News (2002-05-17). Has political correctness gone mad?.</ref>