Blackboard
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A blackboard or a chalkboard is a reusable writing surface on which text or drawings are made with sticks of calcium sulphate or calcium carbonate, better known as chalk.
Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone.
Design
A blackboard can simply be a board painted with a dark matte paint (usually black, occasionally dark green).<ref>Template:Cite web</ref> Matte black plastic sign material (known as closed-cell PVC foamboard) is also used to create custom chalkboard art.<ref>Template:Cite web</ref> Blackboards on an A-frame are used by restaurants and bars to advertise daily specials.<ref>Template:Cite web</ref> Adhesive chalkboard surface is also available in stores as rolls of textured black plastic shelf covering, which is applied to the desired wall, door or other surface.
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 porcelain-enameled 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.<ref name=buzbee />
Lecture theatres may contain a number of blackboards in a grid arrangement.<ref>Template:Cite web</ref> 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.
Chalk sticks
File:Chalkboard-writing.ogg Chalk sticks are produced in white and in various colours, especially for use with blackboards. White chalk sticks are made mainly from calcium carbonate derived from mineral chalk or limestone, while coloured chalk sticks are made from calcium sulphate in its dihydrate form, CaSO4·2H2O, derived from gypsum.<ref>Template:Cite web</ref><ref>Template:Cite journal</ref> Chalk sticks containing calcium carbonate typically contain 40–60% of CaCO3 (calcite).
Issues with use
Chalk dust can aggravate respiratory conditions such as asthma and allergies, according to the American Academy of Allergy, Asthma and Immunology (AAAAI).<ref name="Reading, Writing, and Wheezing? Not Necessarily">Template:Cite web</ref> The dust can also damage or interfere with dust-sensitive equipment, including computers. Chalk sticks wear down quickly and are prone to breaking unless held in a protective chalk holder. Over time, blackboards may experience “ghosting,” in which residual pigment from chalk or chalk markers absorbs into the surface and cannot be fully erased.<ref>Template:Cite web</ref>
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.<ref>Template:Cite journal</ref> According to a study run by Michael Oehler, a professor at the University of Cologne, Germany, humans are "predisposed to detest" the sound of nails on a blackboard.<ref>Template:Cite web</ref> 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.<ref>Template:Cite magazine</ref>
Etymology and history
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The writing slate was in use in Indian schools as mentioned in Alberuni's Indica (Tarikh Al-Hind), 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.<ref>Template:Cite book</ref>
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 16th century.<ref>Template:Cite book</ref> The term "blackboard" is attested in English from the mid-18th century; the Oxford English Dictionary provides a citation from 1739, to write "with Chalk on a black-Board".<ref name=OED>Entry for "blackboard, nTemplate:-", in the Oxford English Dictionary (Third ed., 2011)</ref> The first attested use of chalk on blackboard in the United States dates to September 21, 1801, in a lecture course in mathematics given by George Baron.<ref name="Ambrose1999">Template:Cite book</ref> James Pillans has been credited with the invention of coloured chalk (1814); he had a recipe with ground chalk, dyes and porridge.<ref>Template:Cite book</ref>
The use of blackboards changed methods of education and testing, as found in the Conic Sections Rebellion of 1830 in Yale.<ref>Template:Cite journal</ref> Manufacturing of slate blackboards began by the 1840s.<ref name=buzbee>Template:Cite book</ref> Green porcelain enamel surface was first used in 1930, and as this type of boards became popular, the word "chalkboard" appeared.<ref name=buzbee /> In the US green porcelain enamelled boards started to appear at schools in 1950s.<ref>Template:Cite journal</ref>
Gallery
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An advertising blackboard in Taipei, Taiwan, 2019 -
Mathematics on a board, 2017 -
Teacher explaining the decimal system of weights using a blackboard, Guinea-Bissau, 1974 -
An Austrian chemist with colored chalk, 1970 -
A schoolboy in Seattle, WA, USA, 1961
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See also
- Blackboard bold
- Blackboard Jungle
- 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
- Einstein's Blackboard
- Hagoromo Bungu, Japanese chalk company
- Sidewalk chalk
- Simon in the Land of Chalk Drawings
- Slate
- Tacita Dean, an artist who often uses blackboards in her work
- Whiteboard