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No expert here, but you may have a very high quality finishing stone there. Can you provide some pics of the Asagi? Any stamps on it?
Whatever it is, you should try it and see how it works for you. Some options are to i) make up a ~fairly thick slurry and hone until the slurry is sticky, then refresh and repeat (often several times...depending...), finally finishing on a ~paste, ii) dilute the slurry through several cycles, or iii) hone on water. I would certainly play with it to find out what works best as each hone and method seems to have their own unique way of responding (imagine that... ). I like using a small, 'credit-card' size DMT 325-grit for the slurry 'stone'.
I took the liberty of moving this thread to the appropriate section.
I can't add much else than what Steve already posted.
You can combine it with your Coticule in many ways. You could for instance do the first part of Unicot with the Coticule, and the taped steps with the Japanese hone. That would give you a very good idea of its finishing abilities, because the secondary bevel, which forms the very edge, is entirely and solely produces by the hone you used. And when done well, you can be absolutely sure that the edge has the maximum keenness that hone will ever provide. It's my favorite and first test for unfamiliar hones.
Did you post a pic of the stone?
I am not seeing it.
I agree with Bart, although I test after 12k Super Stone, which I know can give me say 95% of what I consider to be smooth and sharp edge. Depending on the stone you can use Jim's method of honing, which IMHO is great for slow stones.
A variation of the method can be used with medium fast stones, and with fast stones it's entirely up to experimentation how much slurry, if at all, needs to be used.
Maxim has great reputation for carrying top quality stones.
He recently got into straights so the stone is tested on a razor, and if it is said it is suitable then it is.
Please let us know how do you like the stone when you have a chance to test it on a few razors.
^^^ Very nice looking stone. I notice that he also has some nagura listed for reasonable prices. You might want to think about picking up 2-3 of them: botan (or tenjou) and mejiro are shown as being available, and koma is another one of interest if he has it. The different naguras (coarser to fine as listed above) permit you to work your stone essentially from lower grit to higher grit (for lack of a better description...) and then to finish on the asagi.