
what kind of ink does Robert Crumb use when drawing?
Since Robert Crumb uses a Rapidograph pen, when drawing, I would assume that he uses Rapidograph ink. There are many types of ink that can go into a Rapidograph pen, but the most common is Ultradraw.
Ultradraw ink was created to provide technical pen users a rich, non-smearing, black India ink with a long open time for non-clogging. It says on the bottle that it is waterproof, (but if you try coloring/painting over it, there is some smearing) dries quickly on all drawing surfaces and is also suited to airbrushes, crow quills and calligraphy pens. In a .75 oz. filler bottle.
The Crumbs Talk (English)