It is common for draftsmen to sprinkle SCUMEX (powdered rubber eraser) on tracings prior to doing any drawing on it. This reduces smearing of the pencil marks and such and results in a cleaner tracing.
At a former employers we had replaced the Scumex at one draftsmans desk with dried parmesian cheese. It looked about the same. It was extremely interesting watching him draw for a while and then begin to smell the paper. Took the poor dude almost 10 minutes to guess that he had been gigged!