Dave Burnard
>we're "birds of a feather" then. I finished mine, a hard way, shortly after I had switched careers and during the rapid process of forgetting more than I ever knew. Lucky for me, I was walking down a street in North Berkeley, puzzling over x-ray radiative transfer through highly magnetized superheaded plasma, when I walked past one of the 2 japanese tools stores there. ;)

The characterization of manmade stones having "uniform grit size" and manmade stone having "random grit sizes" may be part of the problem. In order for a stone to effectively sharpen at all, the distribution of particle sizes has to be pretty narrow. It only takes a few outliers from the previous stones grit range and you'll never remove all of the coarser scratches (since you'll constantly generate new ones).

I think it may have to do with the relative hardness/softness of the abrasive particles themselves. A paste of diamonds doesn't break down, but a paste of something softer will so that such a stone (manmade or natural) can change grits with the paste.

If I had one stone of perfectly hard 8000 grit abrasive and a second stone of softer 8000 grit abrasive that broke down to form a paste of smaller particles - which one could produce a better edge? Which bevel would be shinier? I know I don't know enough about that's actually going on at the microscopic level to say.