Asked by: Mark Musgrove, USA
The Romans and Egyptians used a lead stylus to write on papyrus but the wooden pencil has always contained graphite.
The original source was a single huge deposit of graphite that was discovered in the 17th Century in Cumbria. This was pure enough to simply saw into sticks and place in wooden cases.
Later, powdered graphite was mixed with varying amounts of clay to adjust the hardness of the pencil.
There's a classification system so we know how hard a pencil is. HB is the standard hardness, 9H the hardest and 9B the softest.
Read more:
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.
