I recently purchased a package of new pencils with a range of 'leads' and am learning about them and pencil history. Pencil 'leads' come in a range. They are typically categorized as H (hard), B (soft; darkness), F (sharpens to fine point) or HB (hard and black). For the H and B pencils, there can be a number, added to the letter, that distinguishes the hardness of that 'lead'. H (hard) leads make lighter lines while B (soft) leads make darker ones. In addition, the higher the number for the H lead, the harder the lead and the lighter the line. For the B lead, the higher the number, the softer the lead and darker the line. In terms of the history of graphite used in the core of pencils, here are some key points: A major graphite deposit was discovered in England in 1565 Graphite is a crystalline form of carbon Pencil graphite has no lead Pencil cores are made of purified graphite power + kaolin (a clay binder) Hard pencils have about 20% graphite; soft