Recording rock art is a bit of a contentious issue. Rubbing is frowned upon and the use of paper covering the surface is viewed as potentially damaging if there is any acidic content in the paper.
Yes, thought that might be the case. Can put your mind at rest though concerning Japanese paper - this is widely used in both Western and Eastern conservation labs. The tamping technique is not as damaging as rubbing (it really is a very gentle technique) but I guess if you have hundreds of people doing it the effect in the long run is the same. 