In the middle of 16th century a previously unkown material that shone like lead ore was discovered in the far north of England.
Wooden or metal tong-like appliances with pieces of this material wedged in were soon in use as a new kind of writing instrument. 

This innovation became misleadingly known as the "lead" pencil.

It wasn't until 1789 that a Swedish chemist was able to prove that the material in question was not actually lead, but a form of crystallised carbon, or graphite.

This rare, and therefore rather expensive, graphite was mixed with sulphur and clay (later with synthetics too).

By varying the recipe, various degrees of hardness could be achieved at kiln temperatures of around 1,100 degrees centigrade.