What is “lead” in pencils?

The lead in modern pencils and crayons is natural graphite mixed with clay to give it the desired degree of hardness. Graphite, one of the softest of minerals, is a crystallized form of carbon and is chemically identical with diamond, the hardest mineral. In nature graphite occurs in both crystalline flake and amorphous forms. It was originally called lead because it was confused with that mineral, with which it has no chemical relationship, being a separate and distinct element. Before the invention of modern lead pencils actual lead was sometimes used for writing. Conrad Gesner, of Zurich, Switzerland, described “writing sticks” similar to modern lead pencils as early as 1695. Graphite is still sometimes popularly spoken of plumbum, the Latin word for ‘lead.” Graphite, from a Greek word signifying “to write,” was given to the mineral in 1789 by Abraham Werner, German geologist, because it was widely used in pencils. Pencil cores are made by mixing graphite and clay together, pressing the mixture into strings under tremendous pressure, and then straightening, drying and burning them at a high temperature. Graphite resists union with other minerals even at high temperatures and has many industrial uses. It is employed in making crucibles, foundry facings, bearings, gears, steel castings, dry cell batteries, electric tubes, motor brushes and generators, stove polish, paint pigments, lubricants, etc. Synthetic graphite made in electric furnaces competes favorably with natural graphite.