I think the material you use is limited only by your imagination. The only thing to watch out for is the weight factor. If your working on a large wedge a heavy silver spacer can add quite a bit of weight or enough to throw your balance off on the razor. If you have access to a lapidary saw you could cut up and slice all kinds of minerals, semi precious gem stuff. It could get really interesting. I had a razor rescaled by one of our exmembers a while back. He used Mamouth ivory for the scales and used fossil ivory for the spacer.