Japanese Natural Finishing Stones from Kyoto (Awasedo)

Naturally occurring stones, known by the Japanese name of “Tennen Toishi (Natural Sharpening Stone)” can be roughly categorized into several distinct groups. Coarse stones (Arado) are sandstone (eg. Oomura), Medium stones (Nakado) are claystone, quartzs-trachyt, tuff, andesite (eg. Aoto, Amakusa, Numata, Aizu, Iyo, Sakeki, many many others.), and Finishing stones (Awasedo) are ganister, silica shale. Within these stones, only the ones that fulfill all of the below conditions are qualified as sharpening stones.

- Harder than steel.

- Fine enough to sharpen the blade to desired sharpness.

- Sharpening particles are dispersed evenly.

- New sharpening particles surface as you sharpen.

- The lubricant (water) can be absorbed to certain extent.

- Stones that are found near Kyoto carry all these characteristics, as a result of a fortunate series of oincidences in tectonic activity.

It is generally accepted that the quarrying of Awasedo (Finishing Stones) begun about 800 years ago in the Kamakura period. Nakayama, Oozuku, Shoubu, Hideriyama, all have different characteristics, and will produce different results, but all fall into the Awasedo category. All of these stones are quarried from the same stratum, sporadically distributed around the west side of Kyoto city. This stratum is called Tanba Mesozoic.

The story of this stratum begins in the Paleozoic Permian era, 2 billion to 2.8 billion years ago. Clays carried by the wind and the remains of microbion called Radiolaria (Phosphoric Acid Calcium CaHPO4) which inhabited the deep sea, accumulated silently and slowly at a rate of approximately 1mm per 1000 years. This accumulation occurred thousands of kilometers away from Japan around present day Hawaii , and resulted in various strata, all with differing characteristics.

Heavier substances such as oxidized iron (Fe2O3) precipitated first and formed the “kawa (the skin)” and the remains of Radiokaria and the clay settled on top of that consisting silica shale. When the ocean was calm the settlings formed stratum that can be used for sharpening stone, and when rough formed “gokudou” stratum which has too many impurities thus cannot be used for sharpening stones.

The accumulation mainly consisted by remains of Radiolaria formed chert. Pure chert is so hard that when struck against other hard objects, a spark results. Unlike this, the accumulation which has more clay content became stones that are more suited to Awasedo, namely the silica shales. These are the stratum which were formed by a mix of the remains of Radiolaria and clay, the latter acting as a cutting substance and the former as binding or glue and at the same time absorbent matter of lubricant (water).

Many people has asked me how is it possible that these stones are only found in Japan and only around Kyoto. When I was talking to my good friend who edited this article for me, he mentioned it must be like Cuban cigar. He told me that although the growers in Cuba exiled to central American countries under Castro regime, and tried to grow Tabacco leaves on a land that is very similar to Cuban soil, could never reproduce the original quality. I am not familiar with cigars, but same thing can be said with wines. A certain Oz winemaker searched for a land that is similar to the renowned Romanee Conti vineyard and tried to make a wine that can match it, but it is totally different, although ve~~~ry good (and so cheap!) There must be so many examples like this.

On Naori

Depending on how far the accumulation took place from the origin of the Radilarias ooze (volcanic activity which cause the ooze to be dispersed into air) the formation of the stratum changes.

- Ai-ishi Naori

The closest from the origin where the particles were the largest, thus heaviest, formed the stratum structure called “Ai-ishi naori”. This structure (naori) can be seen in Hideriyama quarry. The silicic-shally and chert settled one layer at a time in cross grain, which affects the eveness and the hardness of the stone.

- Chu-ishi Naori

Further away from the origin, formed the stratum structer called Chu-ishi Naori. This naori can be seen in Atago, where the silicic-shally strata and gokudou strata are settled one layer at a time in flat grain, which has less influence from chert, even in grain but tends to be soft.

- Hon-kuchi Naori

The best naori for sharpening stone. Furthest away from the origin where only the lightest and finest particles can reach, formed the naori called Hon-kuchi Naori. This naori includes various super famous quarries neighbouring west and east side of Mt. Atago . The quarries on east side of Mt. Atago , called Higashi-mono (East stones) are considered to be the best quality among all Japanese natural finishing stones. These are Nakayama, Okudo, Oozuku, Narutaki, Shoubu, Kizuyama, and only second to Higashi-mono is Nishi-mono (West stones) which are found on the other side of Mt. Atago , such as Oohira, Sinden. There are two more quarries found in far nor-east of Kyoto called Sougandani, Takashima and these quarries are of Hon-kuchi naori as well. This naori has a unique and complex naori structure where the chert stratum separating the silicic-shally stratum has gokudou stratum in between, the silicic-shally stratum has less influence from the chert, thus even in texture and very hard.

There are total of 80 stratum in this naori, and the detail is as below.

Aka-pin
Tenjyou suita (uchigumori, nagagumori, sotogumori, shiro) x4
Hachimai x8
Senmai x2
Tomae x48
Aisa x4 (Karasu is sometimes found in this strata)
Namito x8
Hon suita x6
Shiro suita x2

Finally, please consider this guide as a general overview. There are inferior Nakayama stones and superb Bajiyamas, You never really know until you try the stone. Another consideration is what is known as a “marriage” between the steel/iron and the stone. A stone that performs well with White Steel #2 might be almost unusable for Blue Super steel, and vice versa. For these reasons our policy is to never sell a stone without testing and to also accept returns for all stones sold directly by us.