"Since you didn't mention the purpose behind your question"
I mean, what would be the maximum thickness of the edge for a knife (or razor) to be shaving sharp.
I read somewhere that obsedian (sp?) is probably the sharpest cutting tool in existance.
I think that edge geometry, heat treating, and type of steel, and also hardness would go more toward edge holding ability than how keen you can get an edge.
I used to work at a place where we sheared large pieces of aluminum. I know that the sheared edge would not last on aluminum, but it is sharp enough to do a job on your bare hands.
The same can be said for 303 Stainless, but I don't think either would have a very long lasting cutting edge.
There is also something about grain size and the finer the grain size, the sharper you can get the edge.
