This material is Plumbago Graphite dust. It is manufactured by Asbury Graphite of California, and sold as Plumbago PMB 456 to the commercial foundry industry.
Plumbago is a very fine carbon graphite powder used as a parting dust in high temperature foundry work. It is a slick powder that prevents sand from sticking to patterns, or to keep sand from sticking to itself at the parting line of the flask halves. It is also used as a release agent for coating steel core pins when used in aluminum castings. A graphite coating applied to a steel pin before pouring aluminum into the mold will allow the pin be driven out of the finished aluminum casting, thus leaving an accurate bore.
Dust the material onto patterns, sand or core pins using an old sock or parting dust bag. Store unused Plumbago in a sealed container to keep out moisture (and to keep in the Plumbago!!!).