Sharpening Made Easy

Knife Sharpening Information and Equipment

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SHARPENING STONES
USING OIL AND WATER ON STONES

No shop is complete without at least one bench stone, preferably two or more of different grits. I recommend you buy the largest sharpening stones you can afford. Stones for shop use should be approximately as long as the longest knife you plan to sharpen. Remember that Momma probably owns the really big knives around the house, and you will be expected to sharpen her 8 or 10 inch butcher knives. Smaller stones are handy for field use.  Large tool suppliers such as MSC or McMaster-Carr and restaurant suppliers are good sources for sharpening stones.

Natural sharpening stones include both stones found in nature and reconstructed stones. Washita and Arkansas stones are quarried natural stones, but many of the best deposits have been quarried out. Quality is variable, and an 8" stone can be hard on one end and soft on the other. Now many stones sold by these names are reconstructed. The abrasive material is novaculite, a mineral related to flint and quartz containing mainly silicon dioxide. The relative hardness of novaculite is 6.5 on Mohs scale, just a bit harder than file steel.  The original Japanese and Greek waterstones were also from natural sources.  Natural abrasives work well on carbon steel knives, but they struggle with harder tool steels and tougher wear-resistant and stainless steels. For modern steels I recommend stones made with manufactured abrasives and industrial diamonds.

Aluminum oxide, which has a relative hardness of 9.2, is also bonded to form reconstructed stones, including modern Japanese water stones (resin bond) and India stones (vitrified bond).  Originally this material was from natural sources (emery and corundum), but manufactured abrasives have dominated since the early 1900s.

Ceramic stones are made from alumina (aluminum oxide) or silicon carbide in a ceramic bond.  Silicon carbide has a hardness of 9.5 and will sharpen anything except carbide tipped tool bits.  Spyderco and others offer ceramic stones in a wide variety of sizes and grits.

Industrial diamonds are made into hones by bonding them to steel and are therefore also called diamond files. Diamond has a relative hardness of 10. Two very different types of diamonds are used in diamond hones.  Monocrystalline diamond hones last longer because the diamonds do not fracture readily.  Polycrystalline diamond is less expensive.

Diamond hones are made by DMT, Eze-Lap and others. DMT uses monocrystalline diamonds.  EdgeCraft's unique answer to bench stones is the Chef'sChoice 400 series diamond file system.  It consists of rather thin diamond hones that fit on a magnetic holder.  It is a very good value.  EdgeCraft has a good pamphlet on sharpening which you can request from the address at the end of this article.

An inexpensive alternative to stones is silicon carbide sandpaper. A piece of silicon carbide (also called wet or dry) sandpaper glued to a wooden block will work as well as a stone.  Wet or dry sandpaper on plate glass is popular with woodworkers for sharpening plane irons and chisels, and for flattening the sole of planes.  This method is called Scary Sharp by those who promote it. 

USING OILS AND WATER ON STONES

Natural stones tend to clog without oil or water, while most man-made stones can be used dry.  In North America we usually use oil on all sharpening stones.  Much of the rest of the world uses water. Tests by John Juranitch (2) show that best results are obtained with a dry stone. Apparently particles carried in the oil dulls the edge. I prefer ceramic and diamond stones used dry, and my second choice is Japanese waterstones.

I'll leave this up to your personal preference, with the following guidance:

Aluminum oxide and bonded Arkansas stones can be used with oil or dry.  Clean them with paint thinner. Ceramic and diamond stones can be used with water or dry.  Clean them with water and scouring powder when necessary.  Washita and natural Arkansas stones can be used with oil or water, and cleaned accordingly.

Use and clean Japanese waterstones only with water, but store them dry and soak them before using.  (If you prefer to store them wet, protect them from freezing.  Never add antifreeze to the water, it dissolves the bonding material.)

If you have used water on a stone and want to change to oil, let it dry thoroughly, and then oil it.  Once you have used oil on a stone, it is difficult to change back.  *Requires Acrobat Reader getacro 

(1) Sharpening Made Easy by Steve Bottorff
Knife World 2002 ISBN 0-940362-19-8  $ 9.95
(2) The Complete Guide to Sharpening by Leonard Lee
Taunton Books 1995 ISBN 1-56158-125-9 $ 22.95
(3) The Razor Edge Book of Sharpening by John Juranitch
Warner Books 1977 ISBN 0-446-38002-4 $ 19.95

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