Thanks Jim, Micheal and Marta for coming up with some very interesting points. I just found a company on the web called Reade Advanced Materials. They offer diamond and gold dust as well as platinum, quartz, titanium oxide/dioxide and many other powders. I wonder if it would be safe to use these industrial powders as paint pigments. Can you imagine? Flake white step aside, platinum is here.
P.S. try this address:
www.reade.com/home_index.html