A Pencil Can Draw a Line 35 Miles Long

The incredible mileage of a common pencil is a testament to the remarkable properties of its core material, graphite. A crystalline form of pure carbon, graphite is structured in stacked, sheet-like layers. When you press a pencil to paper, the friction is just enough to shear off these microscopically thin layers, which then adhere to the paper's fibers. Each visible mark is composed of countless near-transparent sheets of carbon. This extreme efficiency in depositing material means that a very small amount of graphite can be stretched out over an astonishing distance, turning a solid rod into a line that could trace the path of a marathon.

This writing instrument is also the product of a historical misunderstanding and a clever innovation. The "lead" in a pencil has never been actual lead; early users of a large graphite deposit discovered in 16th-century England mistook the dark, soft substance for a form of the metal. The modern pencil was perfected in 1795 when French inventor Nicolas-Jacques Conté developed a method of mixing graphite powder with clay and firing it in a kiln. This process not only conserved scarce graphite but also allowed for precise control over the pencil's hardness. Varying the ratio of clay to graphite is what gives us the familiar range from a hard, light-marking H pencil to a soft, dark B pencil.