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. The stone provides a slightly rougher finish compared to standard finishing stones. It is optimal for times when you want to quickly sharen a knife. This grinding stone is suitable for any knind of steel knife.