"Periodically Henry [David Thoreau] would work in the family business, and every time he did, he would make some innovation that would improve production. American pencils at the time were inferior to those imported from Europe, especially the German models. American pencil lead was fabricated with plumbago, wax, and glue, and made an irregular, scratchy line. In 1838 Henry did some research and discovered that German pencils were manufactured with Bavarian clay, which was already being imported into Massachusetts. He changed the formulation of the lead and then designed a new grinding mill to produce a fine graphite. The result was a vastly improved American pencil, and the Thoreau family business prospered."
-- From Living at the End of Time, by John Hanson Mitchell (Houghton Mifflin, 1990)