Contrary to popular belief, the lead in everyday pencils is not lead at all, but rather a mixture of graphite and clay. Graphite, carbon and lead leave gray-black marks on paper, but in 1795, a French chemist developed a mixture of clay, graphite and water that, when hardened, also leaves a gray-black mark on paper. That process is still used today.
In 1821, a graphite deposit was discovered in New England and the pencil-making industry in America grew up around this deposit.
The hardness of a pencil is determined by the ratio of clay to graphite in a pencil.
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Grind up clay and graphite in a large metal drum filled with rocks. Rotate the drum to pulverize the graphite and clay into a fine powder.
Add water to the mixture, and blend for up to 72 hours. When the mixture is the right consistency, press the water out, and leave the remaining muddy mixture to dry until it hardens.
Grind up the hardened, muddy mixture a second time, and add more water to create a malleable paste. If the pencil lead is not dark enough, add carbon to make it darker.
Force the soft paste through a thin metal tube with a small opening to make the familiar round pencil lead found in wood and mechanical pencils. Cut the pencil lead rods to the proper length.
Heat the pencil leads in a kiln at 1,800 degrees F until they are smooth and hard. You can dip the leads in oil or wax to create a smoother writing tool. Then insert the lead into pencils or package it for use in mechanical pencils.
This is a manufacturing process and should not be tried at home.