Nick Huckaby apparently said,on my timestamp of 6/03/2005 1:50 AM:

The problem is that a few of the green see-thru chisels have 10-15 percent
chips gone from its plastic striking surface. Since that day I am more careful.
I'm not sure whether the cause is the a 12-oz. iron hammer or the way I pound
them. What's the best way to repair these tool?

You can't easily repair them. Try grinding/sanding to shape?
Or better yet, get another set. They are cheap enough.

The iron hammer would be the cause. Use a mallet.
Wood is a good choice and you can make one yourself.
Rawhide hammers are the best for this, IMHO. But hard to find.
If all else fails, get one of those cheap hammers with one
side rubber mallet, the other yellow nylon. Use the nylon
side: it bounces really well.

It's important that the head of the hammer is wider than the
top of the chisel handle. Otherwise it's real easy to
swing slightly off-centre and end up with a chip.

HTH
Cheers
Nuno Souto
in sunny Sydney, Australia
am