Oilstones. The most useful of all oilstones are found near Hot Springs, Arkansas. They are divided into two classes, known to the trade as the Arkansas stone and the Washita stone. The former is of very fine grain, appearing much like white marble. It is used in sharpening the most delicate instruments, and produces an edge of remarkable keenness. The Washita stone is much coarser in grain, with a color sometimes almost white, but more frequently shaded by lines of a reddish cast. It cuts with rapidity, and with much greater delicacy than would be expected of so coarse a stone. Probably no better oilstone exists for sharpening wood-working and similar tools.

112. Oil is used on an oilstone for the same reason that water is used on a grindstone. To be serviceable, it should be as free as possible from all tendency to become thick or gummy. A good quality of sperm oil, or even lard oil, may be used; olive oil is frequently recommended.