A
chalkboard or
blackboard is a reusable
writingWriting is the representation of language in a textual medium through the use of a set of signs or symbols . It is distinguished from illustration, such as cave drawing and painting, and non-symbolic preservation of language via non-textual media, such as magnetic tape audio.Writing most likely...
surface on which text or drawings are made with sticks of
calcium sulfateCalcium sulfate is a common laboratory and industrial chemical. In the form of γ-anhydrite , it is used as a desiccant. It is also used as a coagulant in products like tofu. In the natural state, unrefined calcium sulfate is a translucent, crystalline white rock...
or
calcium carbonateCalcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
, known, when used for this purpose, as
chalkSidewalk chalk are typically large colored sticks of calcium sulfate mostly used for drawing on pavement or cement sidewalk. It is sometimes used to draw a four square court or a hopscotch board.-Use:...
. Chalkboards were originally made of smooth, thin sheets of black or dark grey
slateSlate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary layering...
stone. Modern versions are often green because the colour is considered easier on the eyes.
Design
A chalkboard can simply be a piece of board painted with matte dark
paintPaint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...
(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
eraserAn eraser or rubber is an article of stationery that is used for rubbing out pencil markings. Erasers have a rubbery consistency and are often white or pink, although modern materials allow them to be made in any color. Many pencils are equipped with an eraser on one end...
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
rockIn geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
but from
calcium sulfateCalcium sulfate is a common laboratory and industrial chemical. In the form of γ-anhydrite , it is used as a desiccant. It is also used as a coagulant in products like tofu. In the natural state, unrefined calcium sulfate is a translucent, crystalline white rock...
in its dihydrate form,
gypsumGypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
.
Uses
Chalkboards are often used in teaching, although in wealthier countries their use has diminished. University lecture theatres may contain a number of chalkboards in a grid arrangement, with each column mounted on rollers to allow the lecturer to move boards into reach for writing and then move them out of reach, allowing a large amount of material to be shown simultaneously. Chalkboards are also used in many establishments (typically
public houseA public house, informally known as a pub, is a drinking establishment fundamental to the culture of Britain, Ireland, Australia and New Zealand. There are approximately 53,500 public houses in the United Kingdom. This number has been declining every year, so that nearly half of the smaller...
s) as a form of advertising often for upcoming events and menus and to record the score in
dartsDarts is a form of throwing game where darts are thrown at a circular target fixed to a wall. Though various boards and games have been used in the past, the term "darts" usually now refers to a standardised game involving a specific board design and set of rules...
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.
Advantages and disadvantages
As compared to whiteboards, chalkboards 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 odor.
- Chalk writing often provides better contrast than whiteboard markers, which helps people read at a distance.
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 (AAAAI), 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 chalkboardScraping a chalkboard with the fingernails produces a sound which most people find unpleasant. The basis of this innate reaction has been studied in the field of psychoacoustics.-The primate heritage hypothesis:...
, as well as other pointed, especially metal objects against chalkboards, 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 blackboard was invented by James Pillans, headmaster of the Royal High School, Edinburgh,
ScotlandScotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
. He used it with colored chalk to teach geography.
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.
See also
- Chalkboard gag from The Simpsons
The Simpsons is an American animated sitcom created by Matt Groening for the Fox Broadcasting Company. The series is a satirical parody of a middle class American lifestyle epitomized by its family of the same name, which consists of Homer, Marge, Bart, Lisa and Maggie...
- Chalkzone
ChalkZone is an American animated television series that aired on Nickelodeon. It was created by Bill Burnett and Larry Huber, and produced by Frederator Studios for the Nickelodeon TV channel...
- Interactive whiteboard
An interactive whiteboard , is a large interactive display that connects to a computer and projector. A projector projects the computer's desktop onto the board's surface where users control the computer using a pen, finger, stylus, or other device...
- Sidewalk chalk
Sidewalk chalk are typically large colored sticks of calcium sulfate mostly used for drawing on pavement or cement sidewalk. It is sometimes used to draw a four square court or a hopscotch board.-Use:...
- Slate
A writing slate is a piece of flat material used as a medium for writing.In the 19th century, writing slates were made of slate, which is more durable than paper and was cheap at the time when paper was expensive. It was used to allow children to practice writing...
- Sound of fingernails scraping chalkboard
Scraping a chalkboard with the fingernails produces a sound which most people find unpleasant. The basis of this innate reaction has been studied in the field of psychoacoustics.-The primate heritage hypothesis:...
- Whiteboard
A whiteboard is a name for any glossy, usually white surface for nonpermanent markings. Whiteboards are analogous to chalkboards, allowing rapid marking and erasing of markings on their surface...