Color? Well, maybe for starters. I’m thinking itching powder. Caustics? Oilly stuff. Lemme look around the shop. I’m pretty sure there’s a dozen ways here to break the poster ripping habbit.
Prussian Blue is a bitch to wash off. I use it for mold making. Anti seize is a pain to wash off too. But doesn’t cause any discomfort. Maybe mixed with chili oil....