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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.
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.
From the 16th century, all pencils were made with leads of English natural graphite, but modern pencil lead is most commonly a mix of powdered graphite and clay; it was invented by Nicolas-Jacques Conté in 1795. [58] [59] It is chemically unrelated to the metal lead, whose ores had a similar appearance, hence the continuation of the name.
The graphite in mechanical pencils is typically much narrower than in wooden pencils, frequently in sub-millimeter diameters. This makes them particularly useful for fine diagrams or small handwriting, although different sizes of refill leads cannot be interchanged in the same pencil unless it has been specially designed for that purpose.
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. [2] [3]
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