Sharpening knives—or cutting edges of any kind—was among the most fundamental of technologies humans invented and one we can least afford to lose.
A good stone and lubricant are the main tools you'll need when sharpening knives.
Of all the time-honored skills withering in the face of modern convenience, sharpening knives is one we can scarcely afford to lose. As a tool-using species, it was one of our first and most fundamental technologies. A sharp knife is essential in controlling our environment, in separating part A from part B without using our teeth. Once humankind loses the ability to create and maintain a sharp edge, we become little more than savages with clubs and microwaves.
Modern slicers and dicers often regard sharpness as an unnecessary extravagance, on par with leather seats in a sports car. But the truth is, far from being a performance option, a keen edge makes the difference between wielding an efficient tool and a dangerous, uncontrollable weapon.
Knife sharpening, like taxes, is a subtractive business. In theory, material is intentionally removed in the hopes that some good will come of it. My own first attempts, however, yielded nothing more than oily fingers and frustration. The process seems deceptively simple — rub the knife against a rock until its steel yields an edge. Eventually, I learned that almost no skill is required at all if one starts with the proper stone, the right lubricant, and a certain willingness to cheat.
Viewed under high magnification, a knife edge has jagged teeth like a saw. The trick in sharpening is to hone these teeth until they are as small as possible while lining them up smartly in a row. This is accomplished by first grinding a bevel onto the knife to establish the cutting edge, then smoothing the bevel with progressively finer stones until the desired degree of sharpness is reached.
Sharper is not always necessarily better. The finer the work, the sharper the knife, and the finer the stone you will need. I read somewhere that Japanese samurai once gauged the keenness of their swords by how many peasants in a row they could halve with one swipe. Such an edge would also be entirely suitable for slicing tomatoes or boning chicken. On the other hand, such a keen blade would dull very quickly cutting linoleum or frozen food.
My favorite sharpening stones are quarried from natural beds of novaculite in Arkansas. The coarsest, thus fastest cutting grade, is called washita, or soft Arkansas. It is light gray to tan with beautiful striations of color that mark its sedimentary beginnings. A washita stone will hone as fine an edge as most people want. For finer polishing and greater sharpness, a hard Arkansas stone the color and texture of fine white marble can be used.
I admit I'm a romantic; sharpening on a beautifully colored rock is the chief advantage of novaculite. There are also many excellent — though less pretty — synthetic stones. The local hardware store will likely skip the romance and carry only these. They are often available as a "combination" stone that sandwiches medium grit for beveling on one side, fine grit for honing on the other. Get the largest one you can. Trying to sharpen a long knife on a small stone is like trying to park a Cadillac in Manhattan.
Use water, kerosene, or special sharpening oil as a lubricant on the stone. I keep the surface of my stone almost submerged while sharpening. It's impossible to use too much. Avoid the temptation to use your favorite 10W-30 or other motor oil; it is too viscous and will make it difficult to feel the stone under the steel, a bit like washing your feet with your socks on. Also avoid dry sharpening. The stone will quickly clog. I periodically use a vegetable brush and hot soapy water to clean the metal particles out of the stone's pores.
Before beginning to sharpen, I use a bright light to sight along the knife's edge. If there is any hint of light reflected from the cutting edge itself, the knife must be rebeveled. For general use, this means honing a constant 24-degree angle along the entire cutting edge — 12 degrees per side. For heavy-duty cutting, increase the angle slightly. I use a medium-grit stone for the initial beveling to make things go faster.
There is one and only one skill in sharpening — finding and maintaining the aforementioned angle as the knife is drawn across the stone. Luckily for me, there is a simple and honorable way to cheat.
Put a stack of pennies on one end of the stone, two for every half inch of blade width. If you start the knife with its back edge on the pennies, this will place the blade at the correct angle. Then, bearing down hard, draw the knife across the stone and down its length as if slicing a firm cheese — an aged cheddar, perhaps. Concentrate. Watch closely to make sure the knife-to-stone angle remains constant. To maintain the correct bevel around the tip of the knife, pivot the handle of the knife upward at the end of each slice. Take an equal number of strokes on each side and go slowly. This will take some patience.
As the blade sharpens, it will just perceptibly begin to drag on the stone. If you are beveling, switch to a fine-honing stone and repeat the process. If you are honing, it is time to check the edge. I test the edge on my thumbnail. If sharp, the knife will catch in the nail; if very sharp, it can whittle small curls of nail-like wood shavings.
As with any culturally important activity, there are certain taboos to observe. Avoid those kitchen knife sharpeners in which the knife is dragged through a slot. These shred the steel at a microscopic level, leaving the edge ragged and quick to dull. Don't rely on a sharpening steel instead of a stone. Using a steel may be picturesque, with blades and elbows waving about in the air, but it is useful only for touching up an already good edge and will not sharpen a dull one. And don't use a motorized grinder. Heat buildup on a grinding wheel can draw the temper out of steel almost instantly, ruining a good knife's ability to hold an edge.
The cutting edge of all human technology has always been defined in terms of its best cutting edge: first stone, then copper, bronze, iron, and finally steel. Now we're supposed to be a bit more technologically oriented, but we still have onions to dice. So long as there is some part of modern life that is not preportioned and shrink-wrapped, we will need good, sharp knives. And good knives ought, now and then, to taste a bit of oil and to feel the bite of a good stone.
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