Pencils don’t contain lead and never have, but write with graphite, a pure carbon isotope (diamonds being another form of pure carbon). Graphite deposits have been mistaken for lead, however, and pre-pencil writing styluses were made of lead, perhaps explaining the misnomer.
Pencils work because the graphite’s carbon atoms are arranged in sheets, bonded strongly to other atoms to the side of each other, but only weakly to those sheets above and below. Accordingly, they “rub off” easily, such that pencil marks are sheets of carbon atoms.
Pencil-ready graphite is so delicate it must be encased in something to be usable, and before hollowed-out wooden tubes, early pencils were graphite wrapped in paper or string.
The uses of the pencil informed its naming. Pencil comes from “pencillum” or “fine brush” in Latin, and graphite comes from “graphien” or “to write” in Greek.
The graphite pencil went about 200 years before it got that pink eraser attached. Before that, bread crumbs did the trick.
Famous natural philosopher and writer Henry David Thoreau was also part of the very successful John Thoreau & Company family pencil business, and himself developed many major innovations to pencil quality and manufacture.
The letters and numbers on pencils, including that testing favorite yellow “No. 2”, indicate the formulation of that pencil’s graphite for blackness, hardness, and ability to sharpen to a fine point.