Graphite and clay are crushed into a fine powder in a rotating drum containing large rocks. Water is added and the mixture is blended for up to three days. The water is pressed out of the mixture, leaving a gray sludge that is air-dried until it hardens.
The dried sludge is ground into a powder, water is added again, and the mixture is blended to form a soft paste. Carbon black may be added to increase the dark-ness of the lead. The paste is extruded through a metal tube to form thin rods that are cut into pencil-length pieces--called leads--that are then dried. The leads are heated in an oven to 1,800 &°F (about 1,000 °C) or higher to make them smooth and hard. The ratio of graphite to clay can be adjusted to vary the hardness of the lead: the more clay, the harder the lead; the harder the lead, the less graphite comes off onto the paper, making a lighter line.
Pencils are made by cutting blocks of wood into slats that are machined to form a groove (two to nine per slat) to place the leads. A second slat is glued onto the first, sandwich fashion, then individual pencils are cut from the sandwich and sanded smooth. The pencils are next painted with five to eight coats of paint, and a recess is cut for the ferrule--the metal ring that holds the eraser. The ferrule and eraser are crimped into place, and a metal stamp is used to press a label onto the pencil.
Matt: CORRECT
Record: 229-180
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