In the early 16th century, in the northern English county of Cumberland, people discovered a shiny black mineral that was used for the precursors of the present-day pencil. They believed it to be a lead ore. It was not until the late 18th century that it was discovered to be pure carbon – as is diamond. The substance was named graphite, from the Greek “graphein” = to write. In the late 18th century it became possible to produce pencils in various grades of hardness by mixing the graphite with clay. The "lead" pencil never really had anything to do with lead, but the misleading name has been retained to this day.

Surprisingly, despite the long history of black lead pencils, there is no internationally standardized hardness scale. All pencil manufacturers work to their own hardness classifications. 

The CASTELL® hardness scale to which pencils are manufactured within Faber-Castell has remained unchanged since 1910.

A Block of Graphite