Since 1795, pencil leads have been made by combining graphite with clay, extruding the mixture into leads, firing the leads, and then impregnating them with wax. The proportion of clay to graphite and the amount and nature of the wax determine how soft the resulting lead will be.
The pencils used by artists and draftsmen are graded from 9B, the softest, through 8B, 7B, and so on to B, HB, both of medium softness, F, H, 2H, and on to 9H, the hardest. The extremes of the range are little used and difficult to obtain. Probably the most popular grade among artists is 2B.
The standard wooden artists' pencil is 7 inches long with a lead 2 mm in diameter. Two millimeter leads are also used in lead holders, popular with draftsmen. The point on a 2 mm lead in a lead holder is made with sandpaper or a lead pointer, but leads that do not require sharpening are made in diameters of 0.3, 0.5, 0.7 and 0.9 mm for draftsmen's mechanical pencils.
A close relative of the artists' pencil is the graphite crayon, made in diameters of 7, 8 and 12 mm.
Office pencils are graded on a different scale:
The number 2 pencil has acquired a certain cachet from being used to darken the bubbles on the answer sheets of machine-scored multiple-choice tests.
Today most office-type mechanical pencils accept one of the lead sizes used by draftsmen, usually 0.5 mm, but leads with diameters of 0.2, 3, 3.15, and 5.6 mm have also been offered.
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Last revised: 1 February 2010.