The Whetstone Quarry

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The oil for honing that Olmstead mentioned helps to prevent this last problem by holding the metal particles in suspension and keeping the grit clean. The suspended particles of grit also aid in polishing the edge. The water that is used on sandstones for grinding also washes away worn particles and softens the surface of the stone so that it will wear more readily.

Olmstead said that the McCauley stones will "set a fine edge" because "their grit is both fine and sharp." The size of the grit determines how finely the metal surface will be worked by contact with the stone. Abrasive stones work by scratching away the metal sur face. When you grind a chisel on a sandstone wheel, the large particles take deep, widely spaced scratches out of the surface. This quickly shapes the metal, but leaves the edge too rough and ragged to part the fibers of the wood cleanly. When you then hone this edge on a stone with smaller particles, the scratches produced are shallower and closer together. The result is a polished edge that is finer and keener, and one that will meet with less resistance as it is forced through the bundles of cellulose that we call wood.

The finest stones are those that have the smallest grain size and the least amount of foreign matter between the abrasive particles of the rock. The highly regarded Arkansas stones can be almost pure silica and appear pure white. Foreign matter colors stones and affects their cutting action by dispersing the actively abrasive grains so that the scratches they make are farther apart. These impurities can cause a great variation in how the stone will wear, faster or slower, and will determine in large part the tendency of the stone to glaze.

Carpenters generally prefer a soft, fast-wearing stone, both because it cuts quickly and because the broad blades of carpenter's tools will wear away the stone evenly across its surface. The best way to obtain a final edge on a soft or porous stone is to draw the blade backward across its face. I usually do this for a few strokes after I work the edge in a circular motion on the whole surface of the stone.

The narrow tools of carvers would quickly gouge out the soft stones that carpenters and joiners usually use. They must have as hard a stone as possible to resist irregular wear. The hard black Arkansas is their stone of choice.

CARE OF STONES

All whetstones need to be kept in a wooden box to protect them from breakage, dirt, and the elements. A stone that is exposed to the sun will harden and tend to glaze. Clean your stone with plenty of oil or water after each use and put it away. The wooden box will retain some of the oil or water and keep the stone fresh for its next use.

Protect the surface of the stone by working the tool being sharpened over the whole of its width, not just to one side. Inevitably, the ends of the stone will get to be higher than the middle. When this gets to be a nuisance, you can resurface the stone by rubbing it against another one (a chunk of sandstone is excellent) or on a sheet of abrasive paper set on a flat surface.

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