I'm not making a moralistic judgement, its like asking if medical testing is okay or not, its a case by case kind of thing. I just thought the dissolving aspect hadn't come up at all. If it's known to be badly corrosive, and the stone something needing pointed out for posterity, a bad pic and a planned return trip might be better.

I do wonder now if pictures with gorgeous golden toned highlights might be rockart I'd want to avoid touching now though.... :-/