Knife Sharpening

Section Four: Sharpening Basics Before we get into sharpening systems and the actual mechanics of sharpening, it helps to understand some of the basic principles. These are the burr, the sharpening angles, the abrasive, consistency and sharpening strategy. They apply no matter what sharpening method you choose. The Burr First and most foremost is the burr. The burr is your friend. A burr, or wire edge, is a rough, almost microscopic, raised lip of metal that forms when one edge meets the other. It is the only way to be absolutely certain that you have fully ground an edge. Essentially you grind one side until it meets the other and pushes up a small curl of metal. If you stop sharpening before the burr is formed, your knife will not be as sharp as it could be. Sometimes you can’t see a burr, but you can always feel it. You check for a burr on the side opposite the edge you have been grinding. Hold the knife blade horizontally and place your fingers or thumb at a 45-degree angle to the edge and pull gently down and away. DO NOT PULL TOWARD THE TIP OR HILT; YOU MAY LOP OFF A FINGER. PULL AWAY FROM THE EDGE. Remember, check the side opposite the one you've been sharpening. You're checking for a very light lip caused by the edge rolling over to the other side. Check at various points along the edge. The burr tends to form quickly at the base of the blade but takes a little longer at the tip. You must feel a burr running all the way from heel to tip to know that you have fully ground that side of the knife. Resized to 81% (was 600 x 449) - Click image to enlarge Hand position for checking a burr. The Angles As we’ve discussed, the 50-degree-plus included angle that comes standard on most kitchen knives is way too obtuse. Leonard Lee suggests anywhere from 5 to 20 degrees per side (10 to 40 degrees total) for general kitchen work. Five degrees per side is incredibly thin and would require a very hard, high quality steel to keep that edge in regular use. For the vast majority of kitchen knives, 15 to 20 degrees per side will provide a significant increase in performance without requiring undue maintenance. Meat cleavers should be a little thicker, say 20 to 25 degrees per side, while dedicated slicers can be taken down to 10 to 15 degrees per side. The best compromise in the kitchen has proven to be a 15/20 double bevel. That is a 15 degree back bevel with a 20 degree primary edge face. Resized to 97% (was 504 x 360) - Click image to enlarge A 15/20 double bevel illustrated. This is an excellent performer in the kitchen. Abrasives You sharpen your knives by scraping away metal. That’s really all there is too it. But there is a huge array of abrasives available. Traditionalists will demand an Arkansas stone. These stones were originally mined from a novaculite deposit in Arkansas. They were graded, from softest to hardest, as Washita, Soft Arkansas, Hard Arkansas and Black Hard Arkansas. However, the best parts of the deposit were mined long ago, leading to spotty quality in the natural stones. They have since been replaced by ground novaculite reconstituted into benchstones. These can be found under the Arkansas Perfect name. Synthetic aluminum oxide stones are very, very hard and don’t wear like natural stones. They clean up easily with a scouring pad and are more consistent in their grading systems. Spyderco and Lansky both manufacture synthetic stones in a variety of grits (see discussion of grits below). Japanese waterstones are considered by many to be the ultimate sharpening tools. Although natural waterstones are extremely expensive and hard to find, reconstituted stones are readily available. These reconstituted Japanese stones are held together by a resin bond, cut very quickly (and wear more quickly as well) and are available in extremely fine grits that will put a high polish on an edge. Synthetic waterstones, as used by EdgePro systems, are formulated from aluminum oxide specifically for knife sharpening. Like Japanese waterstones, they need to be wet in order to cut effectively. Diamond “stones” have man-made diamond particles imbedded in or coated on a base metal. They cut very aggressively and should be used with caution. They were formerly available only in very coarse grits, but that is changing rapidly. According to Leonard Lee, monocrystalline diamonds are preferable to polycrystalline diamonds in a diamond stone. They are nearly twice as expensive, but last much longer. EZE-Lap, Lansky and DMT make excellent diamond stones. There are two other issues related to abrasives that must be considered: grits and lubrication. You Want Grits with That? All of these abrasives come in a variety of grits from very coarse to ultra-fine. Grit refers to the size of the individual particles of abrasive in the sharpening stone. A stone with a finer grit has smaller particles, and produces an more polished edge with less prominent micro-serrations. A stone with a coarser grit has larger particles, produces an edge with more prominent micro-serrations, and tends to abrade metal away more quickly. There are several different grit rating systems, and unfortunately it is very difficult to correlate these different systems. For example, Japanese waterstones are graded differently than diamond stones and both have different numbering systems than the codes found on powered grindstones. Steve Bottorff, author of “Sharpening Made Easy” has taken a stab at it here if you’re interested. What we do know is that you’ll need a coarse to medium stone for shaping the edge and removing the shoulders of over-thick edges. You’ll also need a fine stone for sharpening the final edge. The combination stones found in most hardware stores just won’t do the trick. The coarse side isn’t coarse enough and the fine side isn’t fine enough. Any of the sharpening systems mentioned later will come with appropriate stones. In very general and imprecise terms, stones rated lower than 300 grit are coarse, 300-400 are medium, 600+ are fine and 1200 and up are extra fine. Japanese waterstones have their own grit rating system. They cut so quickly that anything below 800x can be considered coarse, although they’ll leave a much more polished edge than a corresponding Western stone. 1000x and 1200x can be considered medium and medium-fine and make an excellent general purpose stones. Waterstones can go up to 8000x, but that’s really overkill for kitchen purposes. The stones that come with Spyderco’s Sharpmaker are listed as fine (the white stones) and medium (the grey stones). The grey has been compared to an approximately 800x waterstone, the white to a 1200x waterstone in effect. The synthetic waterstones from EdgePro systems also have an idiosyncratic rating system. The coarse stone is listed as 100, the medium as 180, the fine 220, extra fine 320, ultra fine is 600. However a conversation with Ben Dale, owner of EdgePro, revealed that the extra fine stone is equivalent to a 1200x Japanese waterstone and the ultra fine equivalent to a 2000x Japanese stone. The basic system comes with a medium and fine stone, which should be sufficient for most needs, though the coarse stone comes in handy for quickly reshaping bevels. Oil or Water? Everyone knows you need to lubricate your sharpening stone with water or oil, right? So the question is which one is better. Neither. The purpose of a sharpening stone is to grind the edge and remove metal. Oil reduces friction and makes the process much slower. Supposedly oil helps float away metal particles that would otherwise clog the pores of the stone. You can do the same thing by wiping the stone with a damp cloth when you’re done. Steve Bottorff reports that you can clean your Arkansas stones with paint thinner. Synthetic stones clean up with a scouring pad and abrasive cleanser. According to Joe Talmadge, if you have already used oil on your Arkansas stone, you’ll probably need to keep using oil. But if you have a new Arkansas stone, a diamond stone or a synthetic stone, go ahead and use it without oil or water. It will work much better. John Juranitch reports that in his company’s work with meat processing plants they discovered that the metal filings suspended in the oil on a stone actually chip and abrade the edge. Although these chips were only visible through a microscope, the meatpackers readily noticed the difference between the knives sharpened on a dry stone and those sharpened on oiled stones. Waterstones are another matter entirely. Both Japanese and synthetic waterstones require water in order to cut effectively. Japanese waterstones can be damaged if used dry and must be soaked thoroughly before use. Waterstones wear very quickly, revealing new layers of cutting abrasive as the swarf builds up and is washed away. That’s why they are so effective. There is always a new layer of sharp abrasive cutting away at the metal of your edge. By the way, “swarf” is one of those cool terms you get to toss around when you discuss sharpening. Swarf is the slurry of metal filings and stone grit that builds up as you sharpen. Throw that into your next cocktail party conversation and just watch the expressions of awe appear as people realize that you are a sharpening God. Consistency You must be able to maintain a consistent angle while you are sharpening. This can be tough to do, which is why there are so many gimmicks and sharpening systems on the market. They don’t provide any magic. All they do is help you keep your edge at the same angle throughout the sharpening session. Maintaining consistency is a primary reason freehand sharpening with benchstones or waterstones is a little tricky. It takes a lot of experience and practice to keep the edge at a constant angle stroke after stroke using only your hands and eyes. Sharpening Strategy: Coarse versus Polished Edges Related to the grit discussion above, the finer the stone you use to sharpen your knife, the more polished your edge will be. And while it can be a lot of fun to create a scary sharp edge that will cut the tops off of arm hair without touching the skin, it’s really not necessary or ideal for kitchen use. As a matter of fact, leaving the edge of your knife just a little coarse can be a very good thing. This is where we must compare push cutting to slicing. Push cutting involves parting fibers and requires a polished edge. Shaving, for example, is push cutting. So is peeling an apple or julienning a carrot. You are pressing your thin, finely polished edge through the fibers of the food, pushing them to either side. Slicing, on the other hand, involves severing fibers and requires a toothier edge. Crusty bread, a soft tomato, roast chicken – anything with an outer layer that is tougher than the squishier inside demands an edge that can bite into the skin without crushing the interior. A highly polished edge will simply skate over the surface of a ripe plum until you put enough pressure on it to push through the skin. But the fruit underneath will give way before that happens. Not pretty. Now you must decide. Do you do more push cutting or more slicing? Do you have knives that you use more often for dicing, peeling and julienning? Do you have a knife that is dedicated to slicing? A good basic strategy is to start with a standard 20 degree bevel (a 15/20 double bevel if you’re feeling adventurous) with a moderately polished edge on all your knives. This alone will be a vast improvement over what you might be used to. Then branch out. If you have a knife that is only used for vegetables, a santoku for example, you can take it to a very fine, highly polished edge. A dedicated slicer can be finished on a medium-fine grit stone, leaving the edge slightly coarse. Your chef’s knife can be somewhere in between. There is one caveat. The thinner the edge, the finer it will need to be to avoid excessive damage. A coarse edge wears more quickly and requires more maintenance. This is usually not an issue unless you like your edges very thin. Then a polished edge will last longer. Of course if you have a very thin edge it will probably push cut through materials that a thicker edge might have to slice through, so you’re not losing any slicing performance. If you’re really nuts you can create a dual edge on your knives. This would be a slightly coarse section at the back of the blade near the choil or bolster. The rest of the blade would be finished on a fine or extra fine stone. That gives you a toothy section for cutting through tough materials as you begin your stroke and a finer edge for push cutting through the rest. Yes, this is only for the seriously deranged.