Mineral pigments (ochre, charcoal, iron oxide, hematite, manganese) were ground into animal fat and applied with brushes or were blown through hollow sticks. The artists, working in confined, possibly dangerous space, under unsteady or flickering light from a torch or oil lamp, incorporated distortions and shadows in the design, along with soot...
http://www.cdc.gov/ncidod/EID/vol11no07/about_cover.htm