Then, as a joke, he wrote, "owned by G. Washington" inside in modern pencil. He used to point it out to people who had no idea that a graphite pencil had not yet been invented back then.

Actually, the graphite pencil- ie a piece or rod of graphite in a case or binding to support it, and to keep hands clean- had been devised soon after the discovery of Graphite in Cumbria, in the 1560's, and was widely used by artists, including Michelangelo's studio

The modern Graphite-and-Clay pencil was patented by a French officer in 1795.

Pedant? where?