new old stock Ohzuku questions

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Senior Member
Jan 13, 2015
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A friend of mine named Greg runs a website called and all the credit goes to him. He figured out the math (quite simple to carry out on a calculator) and it was designed specifically for Japanese natural stones. If you want to figure out the hardness of other stones, you have to figure out a few different, specific things about the makeup of the stones.

This is the scale:

View attachment 184292

Cotedupy knows quite a bit about natural stones, he's a great resource and he's helped me out for sure.


The stone should be an old Stock ohzuku. A least it schould be a reliable tool. 2.7g/mmm indicates a low 5/5. That is exactly what I hoped for, might be manageable to a mediocre sharpener like me. Thank you. :)

With a little more trouble than I like, I need something to cheer me up. What do think about Mikawa Nagura? Ban to meijiro are available.

It looks like my first razor gets an edge at 1k. At least the feel changes, and the bevel starts suction to the stone, not sharp so far. Reading indicated naguras might help to get an nice feeling edge. And of course I will try to polish eventually.

The small corner would make a nice tomo nagura, That leaves the question which rough naguras might support me? Stones from ban to koma are available.

Final stones are a unknown Tsuchima, unknown Kaedeyama, something unknown dark slate and a Shapton 8k.

At the moment I like to focus on sharpening, to get off time, to clear my head. Works only, sometimes, like now.
For razors one traditional way of honing them is through those Mikawa nagura. Botan, Tenjyou, Mejiro will work just fine, though you could add koma after that if you’d like. Then comes a tomo nagura to finish the edge.

It seems like you were implying you’d cut your Ozuku for a tomo nagura, in which case I’d recommend you use a diamond plate to generate a tomo slurry instead.
If I can make a suggestion. Use your existing stones for their slurry to get some experience with how each stone + slurry combo works with each other. I’d also recommend to pick up the King 8K nagura because it is useful and a great value at about $11. As mentioned by musicman above, a diamond plate can allow you to draw slurry off of each, effectively a Tomo slurry. You may already have a diamond or roughing stone.

Personally, I was on the verge of buying a Mikawa set, then a light bulb went off, I have a crapton of stones already and they all double as naguras.
Next up is some flattening on sanding paper. I would prefer to sharpen the razor, to try finer stones. But taking the time to do it step by step might be a short cut.

I was completly wrong about diamod plates on hard naturals. Reading nagura page. What kind of plates are used on hard nats? Thinking of buying a rough plate for years, speeding up initial flattening.
In my case a DMT 325 worked much better and faster as the complete Nagura progression.