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A copying pencil, also an indelible pencil or chemical pencil, [1] is a pencil whose lead contains a dye. The lead is fabricated by adding a dry water-soluble permanent dye to powdered graphite —used in standard graphite pencils—before binding the mixture with clay .
Graphite pencils (traditionally known as "lead pencils") produce grey or black marks that are easily erased, but otherwise resistant to moisture, most solvents, ultraviolet radiation and natural aging. Other types of pencil cores, such as those of charcoal, are mainly used for drawing and sketching.
The graphite in pencils is mixed with clay during fabrication of the "lead" to help hold its shape, and would only burn at greater than 1,000 °C (1,832 °F). [ 10 ] The quantity of graphite particles actually produced during occasional writing would be too small to constitute an electrical hazard.
A mechanical pencil or clutch pencil is a pencil with a replaceable and mechanically extendable solid pigment core called a "lead" / ˈ l ɛ d /. The lead , often made of graphite , is not bonded to the outer casing, and the user can mechanically extend it as its point is worn away from use.
Silverpoint is one of several types of metalpoint used by scribes, craftsmen and artists since ancient times. Metalpoint styli were used for writing on soft surfaces (wax or bark), ruling and underdrawing on parchment, and drawing on prepared paper and panel supports. For drawing purposes, the essential metals used were lead, tin and silver
Unlike the construction of a traditional wooden pencil around a solid graphite core, a mechanical pencil feeds a small, mobile piece of graphite through its tip. An internal mechanism controls the position of the graphite by friction, so that although it remains steady while writing, the graphite can be advanced forward to compensate for ...
Grease pencils are available in several forms. The outer casing may be made of wood (like an ordinary pencil) and sharpened with a knife or pencil sharpener. Other types are covered in paper and sharpened by pulling a string to peel off the paper, needing no additional tools to remain functional.
The first mark sense scanner was the IBM 805 Test Scoring Machine; this read marks by sensing the electrical conductivity of graphite pencil lead using pairs of wire brushes that scanned the page. In the 1930s, Richard Warren at IBM experimented with optical mark sense systems for test scoring, as documented in US Patents 2,150,256 (filed in ...
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