Chalk - Uses

Uses

Chalk is used to make quicklime and slaked lime, mainly used as lime mortar in buildings. In southeast England, Deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines, where the prime object was to remove flint nodules for stone tool manufacture. The surface remains at Cissbury are one such example, but perhaps the most famous is the extensive complex at Grimes Graves in Norfolk.

The traditional uses of chalk have in some cases been replaced by other substances, although the word "chalk" is often still applied to the usual replacements.

  • Blackboard chalk is a substance used for drawing on rough surfaces, as it readily crumbles leaving particles that stick loosely to these surfaces. Although traditionally composed of natural chalk, modern blackboard chalk is generally made from the mineral gypsum (calcium sulfate), often supplied in sticks of compressed powder about 4 in (10 cm) long.
  • Sidewalk chalk is similar to blackboard chalk, except that it is formed into larger sticks and often colored. It is used to draw on sidewalks, streets, and driveways, mostly by children, but also by adult artists.
  • In agriculture chalk is used for raising pH in soils with high acidity. The most common forms are CaCO3 (calcium carbonate) and CaO (calcium oxide).
  • In field sports, including grass tennis courts, powdered chalk was used to mark the boundary lines of the playing field or court. This gives the advantage that, if the ball hits the line, a cloud of chalk or pigment dust can be seen. Nowadays the substance used is mostly titanium dioxide.
  • In gymnastics, rock-climbing, weight-lifting and tug of war, chalk — now usually magnesium carbonate — is applied to the hands to remove perspiration and reduce slipping.
  • Tailor's chalk is traditionally a hard chalk used to make temporary markings on cloth, mainly by tailors. Nowadays it is usually made from talc (magnesium silicate).
  • Toothpaste also commonly contains small amounts of chalk, to serve as a mild abrasive.
  • Polishing chalk is chalk prepared with a carefully controlled grain size, for very fine polishing of metals.
  • Chalk is a source of quicklime by thermal decomposition, or slaked lime following quenching with water.
  • Builder's putty also mainly contains chalk as a filler in linseed oil.
  • Woodworking joints may be fitted by chalking one of the mating surfaces. A trial fit will leave a chalk mark on the high spots of the corresponding surface. Chalk transferring to cover the complete surface indicates a good fit.
  • Fingerprint powder
  • Taken orally, in small doses, as an antacid.

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