Originally Posted by
DaveW
Every natural I've seen has grit "balls" in it (if they are that nicely shaped) greater than 10k grit size to begin with, and if anything has grit in the 3-6 micron size that doesn't let go from its natural binder, it can be driven to razor polishing, as long as it wears.
10k size jis is somewhere south of 2 microns.
The only thing I worry about with a natural finisher is whether or not it will hold its grit without releasing it. If it does, I can use it. If it doesn't, I might be able to use it dry or with oil, but i don't like to do that unless the stone is an oil only stone (like an ark).
I'm always curious about natural grit size equivalences, they should almost be given with a full slurry, and disclosed as being hard enough to hold grit or not hard enough. I had a panic when I got my escher initially because I lapped it and it kept getting rid of grit for the first few razors. I could not get an edge the quality I'm used to off of it. It now finally has a nice shiny surface on it, and releases nothing. it's exactly where I want it, and I can get great edges off of it. I doubt the particle size in it is as small as the 12k grit people usually describe, but since it is hard enough to retain its grits, I can get an edge far better and finer than a friable 2 micron synthetic stone would ever give.
So, I'm backing rich's method with natural stones. If it's of any of the types that hold their grit, shave with it (and I'd add to do it with a known keen edge-taking very plain carbon steel razor). That'll tell you all you need to know.