Sunday, May 13, 2007


Black stone, hard stone

Some time ago, I was looking around in an old tools shop here in Taiwan, and noticed that on the floor was laying a dusty box that looked like one of a sharpening stone. I kneel down to look closer and yes, it is a stone. And a natural one. And one that I had never seen before.

No hesitation, I buy one.

I soon sprinkle it with water and put one of my blade on it. Bad. I quickly put back the stone in a box. It is hard, really hard, too hard. The blade I tried on it would jump, chatter and the feeling was bad.

That was maybe one year ago. Recently, wanting to try again the stone, I have the idea to leave the slurry created on the stone when I hone a diamond plate on it. And there it is.
The stone behaves totally differently. It is like a new stone. The slurry, though in few amounts, transforms the stone.

For chisels, even as narrow as 6mm, plane blades (I have tried so far 48 and 55mm), the stone is now one of my favorite.

I had sent one of this stone to a good friend, and he loved it from the begining. I didn't know why, but he was probably right, knowing his expertise in sharpening. Last week I went back to the store to get 3 more stones, and my friend asked for all 3 of them.

Update / complement may 31th 2007

Here are some pictures of that stone.

Hard black stone from the NanHu mountain in East Taiwan.

I have shown the stone to a temple builder. He was interested about it. After trying it, he found it very hard. However using some stone powder makes the sharpening "smooth" as he said in english. He mentioned the stone to some of his colleagues and asked me how much it costed. I gave it to him.

Interesting to note, is that my friend from America to whom I gave one of these stone, compared it with some other black stones that he has.
He graciously sent me some pictures that I post here with his permission, the comments are inspired from his own ones.

Stone from Guanxi in China. Not as hard as the one from Taiwan, can leave some scratches. Not the same "class" of stone.

Hard black stone from Japan.

My friend did an interesting side by side comparison. His conclusion is that "the stone from China are dark grey but not black. The 2 other pairs, on the left from Japan and on the right from Taiwan, are very similar in color and texture.
Taiwan being a volcanic island may have some geological similarities with Japan. Further test would be to compare the hardness, magnify the stone structure, and obviously a sharpening test on identical blades.

Side by side comparison:
-pair on the left are from Japan
-pair on the right from Taiwan
-bottom from China
Stones from Japan and Taiwan are similar in color and texture

I have found out that a small black nagura (from Japan) seems to "fit" well on the black stone from Taiwan. By "fitting well" I mean it produces a slurry that makes the sharpening smooth. Other method of use of that stone was to create a slurry with a diamond plate. This last method gives very good results.

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