chipping paint.... –
I accidentally found out how to do this once -- I had used thicker coats of crackle finish (I've also heard that plain, white school glue like Elmer's will do the same thing, but I haven't tried it) -- on a sign. I painted the sign, let it crackle and then left it in the sun before I put a sealer coat on it -- and it crackled and chipped.
I don't know if this helps at all...but I thought I'd share it with you at least!
Good luck on your project
"Enthusiasm is one of the most powerful engines of success. When you do a thing, do it with your might. Put your whole soul into it. Stamp it with your own personality. Be active, be energetic, be enthusiastic and you will accomplish your object. Nothing great was ever achieved without enthusiasm."
~Ralph Waldo Emerson~