What's the best method to strip paint from window putty before
repainting it.

The current paint is badly chipped and warped so ideally I need to
remove the paint from the putty to get a decent finish.
I've removed the rest of the paint from the window quite sucessfully
with a heat gun.

I want to avoid replacing all the putty if possible although I don't
mind re-touching some of the putty if that's sensible.

Any suggestions would be gratefully received.

Charlie