A pencil seems too simple to need a factory, yet making one takes many steps. The black core is graphite mixed with clay, and the wood around it is cut, grooved, glued and shaped by machines. The core has never held the metal lead. In 1779, German chemist K. W. Scheele showed that it is pure carbon, and in 1789 it was named graphite, from the Greek word graphein, meaning to write.
Graphite works as a writing material because of how its atoms are arranged. Inside a graphite sheet, each carbon atom is strongly bonded to three neighbors in a hexagonal pattern. The sheets themselves are held to each other only weakly, so they slide apart with a light push. That slippery-sheet structure makes graphite feel oily and lets it leave a mark when dragged over paper.
Diamond is the same element arranged another way. In diamond, each atom bonds to four neighbors in a tight three-dimensional network, which makes it the hardest natural material. In graphite the atoms form flat sheets only one atom thick, and the sheets slip past each other. One element, two arrangements, and two nearly opposite materials.
The recipe for the core decides what kind of pencil you get. Clay binds the graphite together, and the ratio matters: more clay makes a harder pencil, while more graphite makes a softer, blacker one. French inventor Nicolas-Jacques Conté is credited with discovering this.
The wooden part starts as a slat, a narrow strip of cedar. One factory description gives its size as about 7.25 inches long, a quarter inch thick and 2.75 inches wide. Slats are planed flat before a cutter head makes parallel semicircular grooves along one side. Each groove will hold one core.
Then comes the sandwich. Graphite rods go into the grooves of one glued slat, and a second slat with empty grooves is turned over on top. The sandwich is clamped in a hydraulic press until the glue dries. Cutters then cut around the top and bottom halves, and one sandwich yields six to nine hexagonal pencils. Many pencils are six-sided because a round pencil rolls off a desk.
Pencils get a metal ferrule and an eraser at the end. A ferrule is a round metal case, attached to the wood with glue or small metal prongs. The eraser is pushed in, and the ferrule is clamped around it. In one description of a factory line, a heated steel die then presses the company logo onto each pencil.
The eraser has a history of its own. In 1858 an American named Hymen Lipman received a patent for attaching an eraser to a pencil. He later sold the patent to Joseph Reckendorfer for a reported $100,000, though one source says 1862 and another says 1872. An eraser works because rubber grips the bits of graphite and lifts them off the paper.
Words to know
- graphite: soft carbon form
- ferrule: metal band
- slat: thin board
- hexagonal: six-sided
