While there are plastics that don't react with acids (all that well at least) other plastics do react. Also given enough time and/or a strong enough acid, it'll eat up most materials. But as was mentioned, there's a lot of easier ways to strip paint off of a mini
"There is a cancer eating at the Imperium. With each decade it advances deeper, leaving drained, dead worlds in its wake. This horror, this abomination, has though and purpose which functions on an unimaginable, galactic scale and all we can do is try to stop the swarms of bio-engineered monsters it unleashes upon us by instinct. We have given the horror a name to salve our fears; we call it the Tyranid race, but if it is aware of us at all, it must know us only as Prey."