This medium grinding stone is molded with a mixture of abrasive(alumina) and bonding(phenol resin)agents, then fired at moderate temperature(approximately 120-200℃).Just add water and the grinding stone can be used right away. The composite is a natural grinding stone. Since it is hardened at moderate temperature, the abrasive and bonding agents are still effective. As a result, the stone could be damaged if left for long periods(several years or up to a decade), or if it is stored while wet. Also, a half-sharpened knife left to sit could start to rust, so after sharpening, be sure to rinse and wipe the knife. This finishing stone features a standard grit level. Although it is an "all powerful" grinding stone fit for any kind of culinary knife, it is a natural grinding stone composite that makes it well suited for kasumi Japanese knives. The slightly dull accent added when grinding on natural stone is especially beautiful.