Originally Posted by
DaveW
I think the nagura is pulling all particles from the surface of the stone and not just iron oxide particles. I don't know what the composition of the stone is itself, but most stones that have a significant amount of iron oxide are reddish or rust colored (you probably already know that).
If you get a clear bright finish with it, I'd call it good, just not good as a nagura plate where you want the stone to shed nothing. It would seem that a pricey nagura with it is a bit redundant, because the stone is happy to give you what you'd get from tomo, and at least the slurry blackens wheras a very cheap stone would slurry too fast for any slurry to blacken.