A blackboard or chalkboard is a reusable writing surface on which text or drawings are made
with sticks of calcium sulphate or calcium carbonate, known, when used for this purpose,
as chalk.
Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone.
Modern versions are often green because the colour is considered easier on the eyes.
Design
A blackboard can simply be a piece of board painted with matte dark paint.
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 blackboards are made of a rougher version porcelain enamelled steel.
Porcelain is very hard wearing and blackboards made of porcelain usually last 10–20 years
in intensive use.
Lecture theatres may contain a number of blackboards in a grid arrangement.
The lecturer then moves boards into reach for writing and then move them out of reach,
allowing a large amount of material to be shown simultaneously.
The chalk marks can be easily wiped off with a damp cloth, a sponge or a special blackboard
eraser consisting of a block of wood covered by a felt pad.
However, chalk marks made on some types of wet blackboard can be difficult to remove.
Blackboard manufacturers often advise that a new or newly resurfaced blackboard 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 blackboards in white and also in various colours.
These are often made not from chalk rock but from calcium sulfate in its dihydrate form,
gypsum.
Chalk sticks containing calcium carbonate typically contain 40-60% of CaCO3
Advantages and disadvantages As compared to whiteboards, blackboards have
a variety of advantages: Chalk requires no special care; whiteboard
markers must be capped or else they dry out.
Chalk is an order of magnitude cheaper than whiteboard markers for a comparable amount
of writing.
It is easier to draw lines of different weights and thicknesses with chalk than with whiteboard
markers.
Chalk has a mild smell, whereas whiteboard markers often have a pungent odour.
Chalk writing often provides better contrast than whiteboard markers.
Chalk can be easily erased; writing on a whiteboard left for a prolonged period may require a
solvent to remove.
Chalk can be easily removed from most clothing; whiteboard markers often permanently stain
fabric.
On the other hand, chalk produces dust, the amount depending on the quality of chalk used.
Some people find this uncomfortable or may be allergic to it, and according to the American
Academy of Allergy, Asthma and Immunology, there are links between chalk dust and allergy
and asthma 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 blackboard, as well as other pointed, especially metal
objects against blackboards, produces a sound that is well known for being extremely irritating
to most people.
Many are averse also to merely the sight or thought of this sort of contact.
Etymology and history The writing slate was in use in Indian schools
in the 11th century as mentioned in Alberuni's Indica, written in the early 11th century:–
They use black tablets for the children in the schools, and write upon them along the
long side, not the broadside, writing with a white material from the left to the right.
The first classroom uses of large blackboards are difficult to date, but they were used
for music education and composition in Europe as far back as the sixteenth century.
The term "blackboard" is attested in English from the mid-eighteenth century; the Oxford
English Dictionary provides a citation from 1739, to write "with Chalk on a black-Board".
The term "chalkboard" was used interchangeably with "blackboard" in the United Kingdom in
the early nineteenth century, but by the twentieth century had become primarily restricted to
North American English.
The blackboard was introduced into the US education system from Europe in 1801.
This occurred at West Point, where George Baron, an English mathematician, used chalk
and blackboard in a lecture on September 21.
James Pillans has been credited with the invention of coloured chalk: he had a recipe with ground
chalk, dyes and porridge.
See also Chalkboard gag from The Simpsons
Chalkzone Conic Sections Rebellion, an 1830 student
uprising when Yale students were required to draw their own diagrams on the blackboard
Interactive whiteboard Sidewalk chalk
Slate Sound of fingernails scraping chalkboard
Whiteboard Further reading
"The Blackboard: An Indispensable Necessity", pages 21–34 in Tools of American Mathematics
Teaching, 1800–2000.
By Peggy Aldrich Kidwell, Amy Ackerberg-Hastings, and David Lindsay Roberts, Johns Hopkins University
Press, Baltimore, 2008, ISBN 978-0-8018-8814-4.
review Notes