Layers of Japanese sharpening stone mines

Japanese natural sharpening whetstones (toishi, 砥石) are valued not only for their mine of origin but also for their specific geological strata (strata layers) from which they are extracted. Each layer, or sō (層), has unique physical and abrasive properties that make the stone suitable for different sharpening stages, from coarse grinding to mirror polishing. These layers, often identified by Japanese terms such as Tenjō suite via Thomas, are closely linked to the geology of the Kyoto region, especially around Atagoyama and Maryuoyama (Mount Maruo). This paper reviews the main strata, their properties, history, use and value, based on Japanese literature (Toishi Kō, 『砥石考』; Toishi Hon, 『砥石本』) and inscriptions by the masters. At least five sentences are devoted to each layer, highlighting their significance in the art of sharpening.

The main layers of mines

Ikimurasaki (赤ピン, Red Pin)

Ikimurasaki The layer, named for its pink mineral inclusions, is one of the rarer and more desirable layers, often found in the Nakayama and Ozuku mines. The stones in this layer, usually pink in colour, are fine-grained, kneaded and ideal for finishing the kasumi by giving a matt surface. Toishi Hon describes Ikimurasaki stones as "blazing like the sunset, soft as silk" (『夕陽の如く燃え、絹の如く柔らか』). Historical sources indicate that this layer was mined during the Edo period (17th-19th centuries), but due to resource constraints it became extremely rare in the late 20th century. Aka pin The stones are highly prized by collectors and often fetch a market price below the value of stones in other layers. They are valued solely for the aesthetics they provide, but are not particularly suitable for sharpening.

Tenjō suite (天上巣板, Heaven's Nest Plate)

Tenjō suite is the highest grade seam found in the Nakayama, Shoubudani and Aiiwatani mines, consisting of four sublayers: uchigumori, nagagumori, sotogumori and shiro. These stones, often Shiro or Asagi type, are soft, porous and fast-grinding, making them suitable for the final polishing of katana swords, razor blades and precision tools to Kasumi or a mirrored surface. Toishi Kō states that Tenjō suite The stones "reflect the purity of the sky and allow the blades to breathe" (『天の清らかさを映し、刃に息吹を与える』). This layer was mined until the middle of the 20th century, but is now almost exhausted, making the stones extremely expensive, sometimes costing tens of thousands of yen for a small piece. Tenjō suite is particularly appreciated for its aesthetic texture, featuring subtle "cloud" patterns, known as gumori.

Hachimai (八枚, Eight Leaves)

Hachim The layer, named for its structure resembling eight thin leaves, is found in the Okudo and Narutaki mines. The stones in this layer are often hard, dark in colour and suitable for final polishing or for removing minor scratches before final polishing. The craftsmen describe Hachim stones as "firm as mountainsides" (『山の斜面の如く堅牢』, Toishi Den). This layer was mined from the Muromachi period (14th-16th centuries) until the end of the 19th century, but is now rare due to the closure of mines. Hachim stones used for katana swords and kitchen knives to Kasumi finishes, and are prized by collectors for their durability and historical significance.

Senmai (千枚, Thousand Leaves)

Senmai A layer consisting of two thin sublayers is found in the Ozuku and Takayama mines and has a very fine-grained texture. The stones in this layer, often Asagi type, are soft and suitable for final polishing, giving a mirror effect to razors and small tools. Toishi Hon describes Senmai stones as "thin as a thousand layers of silk" (『千の絹の層の如く薄い』). This layer was excavated until the 1960s, but is now extremely rare and its stones are highly prized by collectors. Senmai Stones are coveted for their ability to produce a delicate finish, especially for Japanese traditional razors (kamisori).

Tomae (戸前, At the door)

Thomas The layer, with as many as 48 sub-layers, is one of the most complex and versatile found in the Nakayama, Ohira and Shoubudani mines. The stones in this layer, often Asagi or Another one type, are hard, fine-grained and suitable for both intermediate and final sharpening, providing Kasumi or a mirrored surface. Toishi Kō states that Thomas The stones "open the door to the soul of the blade" (『刃の魂への扉を開く』). This layer was excavated from the 17th to the end of the 20th century, but is now almost exhausted, so Thomas stones are extremely expensive. They are used for high-end kitchen knives, especially yanagiba, and katana swords, and collectors appreciate their variety of colours and texture patterns.

Aisa / Ai-sa (合さ, Confluence)

Aisa layer, sometimes called Ai-saconsisting of four sub-layers, is found in the Narutaki and Okudo mines, sometimes containing Karasu type of stones. The stones in this layer are medium-hard, fast-grinding and suitable for intermediate sharpening to remove scratches. Aisa stones used for kitchen knives and tools to Kasumi finishes, and are valued for their versatility. This layer was mined until the middle of the 20th century, but is now rare and its stones are moderately expensive on the collectors' market.

Namito / Nami to (並砥, Ordinary Stone) ~ Daijyo / Daiji yo (大上, Great Height)

Namito, also known as Daijyo Maryuoyama (Maruo Mountain) is the seventh layer from the top, found in the Ohira and Shinden mines. The stones in this layer, often Karasu or Shiro type, are hard and suitable for initial or intermediate sharpening to remove larger defects. Toishi Hon describes Namito stones as "simple yet reliable as a mountain river" (『山の川の如く質素で信頼できる』). This layer was excavated until the early 20th century and Daijyo The Maryuoyama variant was particularly appreciated for its hardness. Namito stones are used for katana swords and tools to prepare the surface for finer polishing and are available to collectors in larger quantities.

Hon suita (本巣板, Real blister) / Shiki suita (敷巣板, Reference blister)

Hon suite and Shiki Suite are closely related layers found in the Nakayama and Aiiwatani mines, consisting of six and two sublayers respectively. These stones, often Shiro or Asagi type, are soft, porous and suitable for final polishing, giving a mirror finish to razors and kitchen knives. Toishi Kō states that Hon suite Stones "are the true heart of sharpening" (『砥石の真の心』). Both layers were excavated until the 1970s, but are now rare, and their stones are highly prized for their unique "nest" patterns (Suite). Hon suite and Shiki Suite are coveted by collectors for their aesthetics and functionality.

Shiki shiro (敷白, Reference White)

Shiki shiro is specific Shiki Suite a subsoil found in the Ozuku and Takayama mines, with a very pale, off-white colour. The stones in this layer are extremely fine-grained, soft and suitable for final polishing, especially with Japanese razors (kamisori) for a mirror effect. Toishi Den describes Shiki shiro stones as "pure as the first snow" (『初雪の如く純粋』). This layer was mined until the middle of the 20th century and is now one of the rarest, which makes its stones extremely precious. Shiki shiro stones are valued for their ability to produce a delicate, transparent finish that enhances the beauty of the blade.

Conclusion

The layers of Japanese sharpening stones are an integral part of the traditional art of sharpening, reflecting the geological and cultural heritage of the Kyoto region. Each layer - from Aka pin By Shiki shiro - have a unique history, characteristics and purpose, allowing craftsmen to achieve the desired finish, whether it be Kasumi, or a mirror surface. Although most of these layered stones are rare due to the closure of the mines, they remain coveted by collectors and professionals who appreciate their aesthetics, functionality and their link to Japanese tradition. The use of these stones is not only a technical process, but also a respect for nature and craftsmanship.