This paint might be neat on a guitar.

[levantin]

Was going to actually say the same thing.-Lou

Me too. I've still got it somewhere.

[leftykingv2]

If it worked without water it would be cool as hell for sure but that video looked a little hinky to me.

[Force]

It's most likely fairly warm water they're using, cold water takes longer to change the colour.

As for guitars, when the air is cool, you'll just have a mark where you picking arm rests.