These are the finest of the natural stones, known the world over for their unique crystalline structure. True novaculite, these stones remove less metal than manmade stones and polish while sharpening. The resulting edge is longer lasting and sharper, achieved with fewer stones and less effort. Arkansas stones must be used with a lubricant.It keeps the stone's surface from clogging, reduces the effort required to sharpen and keeps it clean. Oil or water may be used, but if you decide to go with oil as a lubricant, you must continue to use oil since water will no longer be absorbed by an oil soaked stone. Hard Black stones are the hardest and finest stones. Used for a honed, highly polished edge. Stone colors may vary.