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Natural water stones from Kyoto 6

Legend stone Uchigumori! You can get high contrast on Jigane and Hagane.

water stones

Uchigumori stone is the final stone for sharpening work. You can get beautiful looking and sharp edge.

There are Hazuya and Jizuya stones from Mt. Ohira.

  • Hazuya: For steel core. Also called Habiki or Hato. Light gray color and soft. A little bit easier to use than Jibiki. You can get beautiful blur on your edge and Hamon quicker.
  • Jizuya: For iron layer. Also called Jibiki or Jito. Dark gray color, a little bit harder, heavier and finer grain than Hazuya. You can produce a bright, black bottom on the soft layer. Jizuya is a rarer stone.

According to my own experience, these differences in Uchigumori stones are very small. Since these are natural stones, it can be difficult to distinguish between them because of natural variation in a particular stone. For the beginner I would recommend the Hazuya.

Normally, Uchigumori stones are supplied at rough chiseled surface, not flatten or polished. The stones are left unfinished because Samurai sword makers prefer to shape the stone surface themselves for their particular application like semi-cylindrical, not flat. If you would like the stone flattened like standard stones, I can do that for an additional fee. We call this chipped surface Hatsuri skin.

#1 Uchigumori, Hazuya, flat surface. In Ohira-yama, Kyoto.
Size 36 x 70 x 204mm. Weight 1,350g.Finest finishing stone. Hardness: HS52.
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Price: JPY150,000 In stock
#2 Uchigumori, Hazuya, flat surface. In Ohira-yama, Kyoto.
Size 19 x 60 x 180mm. Weight 650g include the wooden base. Finest finishing stone. Hardness: HS54.
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Price: JPY31,000 In stock
#3 Uchigumori, Hazuya, Hatsuri surface. In Ohira-yama, Kyoto.
Size 33 x 58 x 196mm. Weight 930g. Finest finishing stone. Hardness: HS52.
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Price: JPY64,000 In stock
#4 Uchigumori, Jizuya, Aka Renge. In Ohira-yama, Kyoto.
Size 40 x 68 x 175mm. Weight 1,300g. Finest finishing stone. Hardness: HS69.
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Price: JPY30,000 In stock
#5 Uchigumori, Hazuya, Akarenge, flat surface. In Ohira-yama, Kyoto.
Size 44 x 70 x 206mm. Weight 1,620g. Finest finishing stone. Hardness: HS45.
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Price: JPY150,000 In stock
#6 Uchigumori, Hazuya, Akarenge, Karasu, flat surface. In Ohira-yama, Kyoto.
Size 40 x 75 x 210mm. Weight 1,500g. Finest finishing stone, 3.83μm. Hardness: HS45.
Extra pictures A B
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Price: JPY150,000 In stock
#7 Uchigumori, Hazuya, Hatsuri surface. In Ohira-yama, Kyoto.
Size 26 x 65 x 183mm. Weight 750g. Finest finishing stone. Hardness: HS44.
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Price: JPY63,000 In stock
#8 Uchigumori, Jizuya, Akarenge, flat surface. In Ohira-yama, Kyoto.
Size 15 x 70 x 205mm. Weight 570g. Finest finishing stone, 3.19μm. Hardness: HS62.
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Price: JPY40,000 In stock
#9 Uchigumori, Finger stone, in Ohira-yama, Kyoto.
Finest finishing stone. Hardness: 5/10 medium hard. The picture is sample.
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Price: JPY10,000 for 50g In stock
#10 Uchigumori, Hazuya, 50% flattened surface. In Ohira-yama, Kyoto.
Size 20 x 62 x 183mm. Weight 590g. Finest finishing stone. Hardness: HS56.
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Price: JPY40,000 In stock
#11 Uchigumori, Hazuya, flat surface. In Ohira-yama, Kyoto.
Size 26 x 64 x 190mm. Weight 790g. Finest finishing stone. Hardness: HS47.
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Price: JPY64,000 In stock
#12 Uchigumori, Hazuya, Akarenge, Hatsuri surface. In Ohira-yama, Kyoto.
Size 18 x 64 x 179mm. Weight 560g. Finest finishing stone. Hardness: HS54.
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Price: JPY45,000 In stock
#13 Uchigumori, Jizuya, Akarenge, flat surface. In Ohira-yama, Kyoto.
Size 25 x 65 x 180mm. Weight 700g. Finest finishing stone. Hardness: HS57.
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Price: JPY50,000 In stock
#14 Uchigumori, Hazuya, Akarenge, Namazu, Hatsuri surface. In Ohira-yama, Kyoto.
Size 24 x 52 x 163mm. Weight 560g. Finest finishing stone. Hardness: HS55.
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Price: JPY45,000 In stock
#15 Uchigumori, Hazuya, Akarenge, Hatsuri surface. In Ohira-yama, Kyoto.
Size 25 x 66 x 176mm. Weight 720g. Finest finishing stone. Hardness: HS37.
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Price: JPY63,000 In stock
#16 Uchigumori, Hazuya, Hatsuri surface. In Ohira-yama, Kyoto.
Size 30 x 58 x 166mm. Weight 790g. Finest finishing stone. Hardness: HS38.
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Price: JPY90,000 In stock
#17 Uchigumori, Hazuya, Akarenge, Namazu, Hatsuri surface. In Ohira-yama, Kyoto.
Size 33 x 64 x 181mm. Weight 980g. Finest finishing stone. Hardness: HS43.
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Price: JPY60,000 In stock
#18 Uchigumori, Jizuya, Akarenge, flat surface. In Ohira-yama, Kyoto.
Size 24 x 70 x 204mm. Weight 895g. Finest finishing stone. Hardness: HS57.
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Price: JPY90,000 In stock
#19 Uchigumori, Jizuya, Akarenge, Hatsuri surface. In Ohira-yama, Kyoto.
Size 25 x 64 x 170mm. Weight 685g. Finest finishing stone. Hardness: HS52.
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Price: JPY60,000 In stock
#20 Uchigumori, Hazuya, Karasu, flat surface. In Ohira-yama, Kyoto.
Size 22 x 70 x 198mm. Weight 750g. Finest finishing stone. Hardness: HS50.
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Price: JPY80,000 In stock
#21 Uchigumori, Hazuya, Hatsuri surface. In Ohira-yama, Kyoto.
Size 31 x 67 x 208mm. Weight 1,070g. Finest finishing stone. Hardness: HS44.
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Price: JPY80,000 In stock
#22 Uchigumori, Hazuya, Hatsuri surface. In Ohira-yama, Kyoto.
Size 35 x 70 x 195mm. Weight 1,250g. Finest finishing stone. Hardness: HS45.
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Price: JPY90,000 In stock

EXPLORING THE MYSTERY OF NATURAL STONE

Some mystery results will appear when sharpening with natural stones. Please check the two pictures below. They are sharpened blade edges with natural stone and synthetic stone. I used a microscope with 100 times magnification.

Sharpened with Ohira stone
Natural stone Ohira about #5000
Sharpened with Kitayama #8000
Synthetic stone Kitayama #8000

The Ohira stone is rougher grained than the Kitayama stone. However the pictures show that sharpening marks from the Ohira stone are obviously finer than the Kitayama stone.

I don't know exactly why this happened. These are my own results according to my own experience with the stones. Though, my experiences are not unique according to some other books and reports.

A. You can sharpen easier and get precise edge.

  1. You can start to sharpen with only a few drops of water. You can sharpen well without clogging and slipping.
  2. Grain corners are rounded, which help remove all ground marks.
  3. Grains becomes smaller and smaller during a sharpening session, so you can sharpen to a more precise edge.
  4. The resulting micro wavy edge will be keener and hold longer.

B. The edge retention is incredible by hardening effect.

  1. When you sharpen until your blade becomes hot, the hardening effect will be strongly on the edge. The burr becomes very small, and you can easily remove it with opposite side sharpening, because the burr becomes brittle with this effect.
  2. The edge retention is very long. So you don’t have to re-sharpen very often. This gives your blade more longevity.

C. You can get beautiful glossy surface of steel and iron.

  1. Gloss of iron. (bottom black brightness)
  2. Gloss of steel. (Attain inside fogginess of Samurai sword)
  3. Matte of edge. (Blur of the edge)

From "Fascinating Kyoto Natural Stones" Kyoto natural stone association (1993).

Also from "Study of natural stone." Japan Society for the Promotion of Machine Industry (2005).

D. Natural stones made of many, slightly irregular layers.

  1. When you sharpen blades, a layer of stone micro-structure is peeled off. There are slight level differences. It effects micro shaping height.
  2. During sharpening, the surface layer is peeled off again and again. So the stone surface always creates a new cutting edge.
  3. Micro grains are grasped by the surface, so the retaining power is extremely stronger than blocky grains of synthetic stone.

EPMA of natural stones


I have also heard that some people think that hardening effect comes from "sulfurization". Natural stones include calcium sulfide and calcium carbonate. During sharpening, a chemical reaction occurs with water and iron. The blade becomes hot and iron sulfide is produced. As a result, the blade has hardening effect. From my own observations with microscope, the sharpened surface looks similar to an etched surface.

Component of natural stones

Synthetic stones are recommended for just shaping. In contrast, natural stones have some miracle effects at later stage sharpening. Please stay tuned for future reports on these sharpening properties of these different stones.

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PS: There are some voices about hardening effect.
Someone said, "Such the effect is nothing. The small burr is just natural stones don't have the strong shaping power like synthetic stone."
I don't have clear answer yet. I feel even the burr of rough natural stone Aoto is smaller than the burr of finer synthetic stones. That might be another question, though.

A great blade smith told me hardening effect is "work hardening" like rolling or forging. His blade hardness was HRC 65. But after sharpening, the hardness became HRC66 - 67. I believe this miracle. I think it appears at harder stone sharpening is easier. (more than 8/10 at my rate). The process might look like lapping, not sharpening or polishing.