Pencil lead From Wikipedia, the free encyclopedia.Pencil lead is the marking substance inside a pencil or mechanical pencil. It is not actual lead (which is poisonous), but rather a form of graphite, which in modern pencil lead is mixed with clay. It is called lead because graphite was originally mistaken with lead and named "black lead" since lead and graphite leave similar marks.
History Graphite was originally discovered in England after a violent storm broke some trees leaving a graphite deposit visible under the roots. Graphite was soon used to write but it was very fragile so it had to be wrapped in a string and later inserted into a perforated cedar wood stick. Early cedar pencils were made of a solid piece of wood but modern pencils are made with two halves glued together with the lead between them. The Napoleonic Wars birthed the modern graphite and clay-based pencil out of necessity. France, under naval blockade imposed by Great Britain, was unable to import the pure graphite sticks from the British Seathwaite Fell mines - the world's only known source of solid graphite. France was also unable to import the inferior German graphite pencil substitute. In 1795 Nicholas Jacques Conté, a Army officer, discovered that firing the available powdered graphite with clay would work as a susbstitute pencil filler.
Hardness Pencil lead is graded by hardness: a greater percentage of clay results in a harder lead. H (harder), F, HB and B (softer) are pencils of average hardness. Pencils ranging from 2B to 9B are softer still and are used for sketching; 2H to 9H are harder than average. A common American #2 pencil is equivalent to HB. In order, the leads are (from hardest to softest) 9H | 8H | 7H | 6H | 5H | 4H | 3H | 2H | H | F | HB | B | 2B | 3B | 4B | 5B | 6B | 7B | 8B | 9B. The harder the pencil the lighter the mark, e.g. "b"s tend to a create darker colour that can be smeared easily.
Mechanical pencils In mechanical pencils, pencil lead is a long, thin rod of graphite, clay, and wax. The most common thicknesses are 0.5 mm and 0.7 mm, others being 0.3 mm, 0.9 mm, and 2.0 mm. Common lengths include 60 mm, 75 mm, and 120 mm. Two-millimeter lead comes 5 1/8" long. Pencil lead is typically inserted at the back of the pencil. Two-millimetre lead is used in a drafting mechanical pencil called a "lead holder", and a "pointer" is used to sharpen the lead. Some Japanese companies, like Tombo, now sell "recycled" lead made from industrial waste carbon.
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