There are three ways to use an abrasive stone in knife sharpening.
The traditional method was to use oil in conjunction with Novaculite, a stone which is commonly found in Arkansas and because of this, these stones are commonly called Arkansas stones.
Arkansas stones come in a few grades from coarse to fine. The "Washita Stone" is the coarsest while the "Black Arkansas" is the finest.
Man made oilstones are now made from Silicon Carbide and Aluminum Oxide. The abrasive grit is pressed and heated like a ceramic to a high temperature until it is effectivly a stone. These materials cut faster than the natural stones but require a lighter touch to achieve the same results. IE, they do not make the edge as sharp as Arkansas stones though this can be offset by grinding the edge using less pressure. Of the manmade materials, Silicon Carbide cuts faster than Aluminum Oxide but the latter produces a sharper edge.
These manmade stones can also be used as water stones as long as they have not been presoaked in oil. Once a stone is soaked in oil it can never be used as a waterstone.
Waterstones such as the ones generally available in the local hardware store are made from Silicon Carbide or Aluminum Oxide. The abrasive grit is pressed and heated like a ceramic to a high temperature until it is effectivly a stone. Silicon Carbide cuts faster than Aluminum Oxide but the latter produces a sharper edge.
Natural waterstones generally come from Japan. They are made from mud or ash or the skeletons of millions of aqautic animals which have been compressed into stone over time as a result of the weight of overlaying rock. This can take millions of years. Japanese "Mudstones" as they are commonly called, can be very fine grit and are generally soft. They can impart a remarkable edge.
Japanese mudstones should be stored dry and soaked for a half an hour before use.
The Japanese also make synthetic mudstones which are also very fine grit and almost as soft as their natural equivalents.
With all waterstones care should be taken to ensure the stone never becomes contaminated with oil.
John Juranich caused quite a stir when he announced some years ago that as a result of testing he believed that both water and oil stones gave a better edge when used dry. Amazing as this might at first appear his claims are not without some foundation. He tested oilstone and drystone techniques in a meatpacking plant. The study was blind as he was relying on the opinions of the meat cutters themselves who had no idea how any individual knife was sharpened. He explains the events in his book The Razor Edge Book of Sharpening which makes very interesting reading.
Juranich believes that the slurry produced by mixing oil and metal and abrasive particles acted like a grinding paste. He says the effect of having this slurry pass over the edge acted like the earth on a plow tip, rounding it off. On examination under electron microscope the oil sharpened edges were chipped.(F1)
He added emphasis to his point by shaving his generous beard on television, with an axe that he sharpened in a matter of minutes, using the dry sharpening method. Since Juranich's revelations the practise of drystone sharpening has grown in popularity.
All stones can be trued by abrasion. To avoid contamination a stone of the same grit is used to lap the stone back to true. Waterstones should be stored dry.
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