David Weaver
I have a lap of pure .09 micron iron oxide pigment from kremer. It is extremely fine and will bring a razor past where I'd have any interest in using it - linen and strop normalize that off.

the interesting thing is that the iron oxide pigment will blacken when a hardened razor is stropped on it - it does some cutting and not just burnishing. I never checked the mohs hardness of it, but some component of it must be at least in the ballpark of iron carbides, as the edge is supremely uniform.

Chris Griggs, who used to post on SMC was vegan and thus had to find something to use as a substitute for a leather strop (neoprene and other artificial materials by themselves just don't do nearly as well as good leather). He really liked the iron ox and tolerated the sharpness better than my face does.