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pencil lead?
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For more on marking an answer as the "Best Answer", please visit our FAQ.The connection between graphite and lead stems from the days of the Roman Empire (and likely before that), when lead rods were used by scribes to write on papyrus. Both graphite and lead leave a gray mark on paper, although graphite is a bit darker. Graphite didn't come into widespread use for writing until after the 1564 discovery of a very pure graphite deposit in Borrowdale, England. At the time, graphite was thought to be a type of lead and consequently was called black lead or plumbago.
Today, 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 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.
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There is also another link between lead and graphite. The Latin root (plumbus) for lead gives us plumber, plumbing and plumb line - all asssociated with lead. The mineral form of pure graphite looks a lot like lead, though lacking its weight. An old name for graphite ore was therefore plumbago. This could therefore explain why materials made from graphite (plumbago) also became known as 'lead'.