As student medical illustrators, we learned all of the illustration techniques of the old masters. I think the only time I used this technique was as a student. The method consisted of applying carbon dust, obtained by rubbing carbon pencils against an abrasive surface such as a metal file, to a prepared surface via dry brushes. Highlights were painted on or scratched out later in the process using fine instruments or erasures. A very specialized paper was used. Wonder if it's even made anymore.
This extremely fragile piece is entering the Lloyd Library and Museum in Ohio as a part of the Vesalius Trust Collection of Art Serving Medicine and Science. I hope to continue to post pieces as they're prepared for shipping.