Your Pencil Has Never Had Any Lead in It

Picture a sheep on a green hillside in the Lake District of England, with a smudge of dark grey on its woolly back. Long before anyone wrote a shopping list with a pencil, the farmers of Borrowdale were using a soft, shiny black stone from their own valley to mark their sheep. It left a clean dark line on wool and, as people soon noticed, on paper too. That stone is the reason we talk about pencil lead today, and it has never had anything to do with lead at all.

What people often get wrong

Almost everyone calls the grey core of a pencil its lead, and plenty of people half believe there really is metal inside. There is not, and there never was. The core is graphite, a soft form of pure carbon, usually mixed with clay. The funny part is that the only real lead in this story belongs to the tools graphite replaced. Before it arrived, people drew with metal points, and the new stone made a darker line that was far easier to rub out.

So where did the name come from? When a rich seam of graphite was found in Borrowdale in 1564, nobody knew what it was, because chemistry was still very young. The stone marked paper much the way lead does, only darker, so people called it black lead, and in more learned writing plumbago, from the Latin word for lead. Over the years black lead was shortened to plain lead, and the name stuck to the pencil for good.

How a stone got its real name

The Borrowdale graphite was so pure that it could simply be sawn into sticks, and the earliest known description and drawing of a pencil appeared in 1565. Solving the mystery of the stone took two more centuries. In 1778 and 1779 the chemist Carl Wilhelm Scheele published work showing that it was a form of carbon, not a metal. About a decade later the mineralogist A. G. Werner gave it a fresh name, graphite, from the Greek word graphein, which means to write.

1. 1564 A rich seam of graphite is found in Borrowdale, England
2. 1565 The earliest known description and drawing of a pencil
3. 1779 Carl Wilhelm Scheele shows that the black stone is carbon
4. 1794 Powdered graphite, clay and water make a new kind of pencil core
5. Today Pencil makers still use a version of that recipe

Pure graphite like Borrowdale's is rare, and in 1794 the French inventor Nicolas-Jacques Conté found a way round that. He mixed powdered, less pure graphite with clay and water to make strong pencil cores. Some accounts give the year as 1795, but they agree on the recipe, and a version of it is still how pencils are made today.

Why graphite writes so well

The trick lies in how graphite is built. Its carbon atoms are joined into flat sheets, each only one atom thick. Inside a sheet the atoms hold on to each other very tightly, but the sheets themselves are only loosely stacked, like the pages of a book with no spine. Press a pencil onto paper and whole layers slide off and stay behind as your line. Diamond is made of the very same carbon, only packed into a tight three-dimensional pattern, which is why one leaves a soft grey line and the other is the hardest natural material on Earth.

Lead was not the only metal caught up in the mix-up. Old writers also called some soft grey minerals molybdaena, from the Greek word for lead, and when a new metal was later drawn out of one of them, it was named molybdenum. So the periodic table carries a small souvenir of the same confusion, and every pencil in your drawer carries the other.