Valve Shims

Hi,
Over the years I have accumulated quite a few shims, most of which are thick ones. Question is as any one ever had shims surface ground down to a thinner size, are they hard all the way through or surface hardened, if so how much can be removed ?
Thanks in advance.
Pat

 

Hi ram,
Thought they might be surface hardened, think it might be a bit risky so wont bother. Always have to fit thinner shims, so end up with a box full of thicker ones, just trying to reuse some of them!
Thanks for reply Pat