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A blackboard (also known as a chalkboard) is a reusable writing surface on which text or drawings are made with sticks of calcium sulfate 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 Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone.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.
A blackboard can simply be a piece of board painted with matte dark paint (usually black or dark green). Black plastic sign material, using the trade name sintra is also used to create custom chalkboard art. 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 (black, green, blue or sometimes other colours). 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 moves 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 usually 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.
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, CaSO4·2H2O (gypsum). Chalk sticks containing calcium carbonate typically contain 40-60% of CaCO3 (calcite).
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.
- Dashed lines can be drawn very quickly using a technique involving the friction of the chalk and blackboard.
- Chalk has a mild smell, whereas whiteboard markers often have a pungent odor.
- Chalk writing often provides better contrast than whiteboard markers.
- Chalk can be easily erased; writing which has been left on a whiteboard 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 (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. Chalkboards writing on chalkboards are not easy to see in the dark. Chalk sticks are notorious for both shrinking upon frequent use and breaking in half when using them, unless the chalk is inserted inside a writing utensil designed to store chalk.
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. According to a study run by Michael Oehler, a professor at the University of Media and Communication in Cologne, Germany, humans are "predisposed to detest" the sound of nails on a blackboard. The findings of the study were presented at the Acoustical Society of America conference and support earlier findings from a 1986 study by Vanderbilt psychologist Randolph Blake and two colleagues found that the sound of nails on a chalkboard annoyed people even when the high-pitch frequencies were removed. The study earned Blake a 2006 Ig Nobel Prize.
Etymology and history
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 the United States Military Academy, 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 (1814): he had a recipe with ground chalk, dyes and porridge.
- Chalkboard gag from The Simpsons
- Conic Sections Rebellion, an 1830 student uprising when Yale students were required to draw their own diagrams on the blackboard
- Interactive whiteboard
- Sidewalk chalk
- Sound of fingernails scraping chalkboard
- Simon in the Land of Chalk Drawings
- WebMD. "Reading, Writing, and Wheezing? Not Necessarily". Asthma Health Center. WebMD.
- Robert Siegel (9 November 2011). "Why Nails On A Chalkboard Drives Us Crazy". NPR. Retrieved 31 May 2016.
- Frances Romero (14 June 2010). "Top 10 Most Annoying Sounds: Nails on a Chalkboard". TIME Magazine. Retrieved 31 May 2016.
- "Full text of "Alberuni's India. An account of the religion, philosophy, literature, geography, chronology, astronomy, customs, laws and astrology of India about A.D. 1030"".
- Owens, Jessie Ann. Composers at Work: The Craft of Musical Composition, 1450-1600. Oxford University Press, 1998.
- Entry for blackboard, n, in the Oxford English Dictionary (Third ed., 2011)
- Stephen E. Ambrose (1 December 1999). Duty, Honor, Country: A History of West Point. JHU Press. p. 19. ISBN 978-0-8018-6293-9. Retrieved 14 February 2013.
- Jo Swinnerton (30 September 2005). The History of Britain Companion. Anova Books. p. 128. ISBN 978-1-86105-914-7. Retrieved 14 February 2013.
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