Sharpening Stone - Natural Stones Versus Artificial Stones

Natural Stones Versus Artificial Stones

Natural stones are less common than they used to be. Historical demand has exhausted most known natural quarries and little effort has gone into discovering new ones due to, and since, the concurrent rise of gunpowder and industrial chemistry: the former obviating the military importance of whetstones, and the latter allowing for the mass production of artificial ones.

As a result, the legendary Honyama mines in Kyoto, Japan, have been closed since 1967. Belgium currently has only a single mine that is still quarrying Coticules and their Belgian Blue Whetstone counterparts. This scarcity causes high prices for a good quality natural stone. Lower quality natural stones have problems with consistent grain sizes, low abrasive particle content leading to "slow" sharpening, inconsistency in hardness, inclusions of large foreign particles of other stone materials, and cracks and other such natural imperfections.

Modern synthetic stones are generally of equal quality to natural stones, and are often considered superior in sharpening performance due to consistency of particle size and control over the properties of the stones. For example, the proportional content of abrasive particles as opposed to base or "binder" materials can be controlled to make the stone cut faster or slower, as desired. Natural stones are often prized for their natural beauty as stones and their rarity, adding value as collectors' items. Furthermore, each natural stone is different, and there are rare natural stones that contain abrasive particles in grit sizes finer than are currently available in artificial stones.

Japanese sword polishing, particularly in the finishing stages, is still most commonly performed with extremely costly and rare natural polishing stones, as the inconsistent grit sizes of the abrasive particles in natural stones will often produce visual results of polishing that reveal characteristics of the steel that the uniform grain particles in artificial stone will not. Some Japanese waterstones are known to reach 50,000+, 75,000+, or even 120,000+ grit in abrasive particle size, while the finest artificial stone sold is the Shapton 30,000 grit stone (though diamond abrasive particles of several hundred thousand grit are available, typically as a suspended liquid or dry powder).

One of the most revered natural whetstones is the yellow-gray "Belgian Coticule", which has been legendary for the edge it can give to blades since Roman times, and has been quarried for centuries from the Ardennes. The slightly coarser and more plentiful "Belgian Blue" whetstone is found naturally with the yellow coticule in adjacent strata; hence two-sided whetstones are available, with a naturally occurring seam between the yellow and blue layers. These are highly prized for their natural elegance and beauty, as well as for providing both a fast-cutting surface for establishing a bevel and a higher-grit surface for refining it. Amongst straight razor users, this stone is considered one of the finest.

The hard stone of Charnwood Forest in northwest Leicestershire, England, has been quarried for centuries, and was a source of whetstones and quern-stones.