[Icorps1970]

If its Hydrofluoric acid it will etch the stone according to
http://www.findstone.com/othprob.htm
Some will cause color changes.
If the vandal did research the monument may be permanently stained or etched.

[concretebob]

Yeah but hydroflouric acid is something you need to be very careful with.
That would be a hoot.
Try to deface the Wall with that, and spill a little on his clothes or skin, wouldn't be hard to find him.
Just listen for the screams.
No Bro, I saw it, I touched it, it's oil.

Quick riddle for ya

Whats wrong with this sentence:
A scientist working in a lab invented a substance which will disolve anything it touched.