Henry Petroski wrote a great book about the history of the pencil. There used to be a mine in Southern England which contained pure graphite, that was found in

Henry Petroski wrote a great book about the history of the pencil. There used to be a mine in Southern England which contained pure graphite, that was found in the 16th century. That graphite could just be cut into sticks and made into writing implements. The modern pencil consisting of powdered graphite with a binder is a response to that mine being exhausted. So it's a substitute for a product that wasn't possible before that pure deposit was found.