Sharp vs. Strong

Posted: November 12, 2011 in General Discussion

by:  Eamon Burke

A kitchen knife is supposed to be, first and foremost, sharp.

Right?

This is a common sense belief; one that is promoted by advertising, sharpening enthusiasts, and end users.  The world is full of dull knives and we are all impressed by a sharp knife, performing it’s task so effortlessly.  A sharp knife seems to say, “Hey, let me do that work for you, I’ll make an easy time of those old tomatoes and that butternut squash.”  It appeals to the part of our instincts that want to get as much as we can for as little investment as possible, and a dull knife is just unacceptable waste.  But is this the most important feature of a kitchen knife?   We need to go back to the beginning.

Some of the first tools man ever used are called “Oldowan tools”, and were blades fashioned from rocks for digging and cutting.   You have to stab the pig with the broken branch and hoist it over the fire to keep it from catching fire, and you have to have the sharp rock to get the legs off a cooked pig without dropping the pig in the dirt and having your buddies help pull them off.   So you go to find the pointiest stick in the wood, and the most acute piece of flint in the cave.  However, you soon find that the ultra-pointy stick will not survive the pig’s hide, and the thin rock will chip on every bone, causing more harm than good(paleolithic gastroenterologists were hard to come by).

No, you’d need more than a pointy object, it would have to withstand the rigors of real use.  So one day, you take some flint and bash it into a shape that still has an edge, but is bulky enough to survive impact.  You use it on the stick to hack down that pointy tip, and there you have it—the first edges.  Some of the first design improvements were “hand axes”, made out of  materials that are often quite treacherous in their own right(quartz, obsidian, flint), and were chipped away to create a usable edge, and altered in shape not to hone for sharpness, but to strengthen the tool and tame its brittle nature.

A knife, when you consider it’s role as a tool used to redirect force, is a series of increasingly less acute bevels.  The face, starting at the spine, is the most acute bevel on the entire knife, and if there were no edge bevels added, it would have to be extremely thin to come to an edge in a usable size.  Any time it needs to be sharpened, the entire faces of the blade would have to be abraded down precisely even, any overgrind at all would cause the edge to wave, and the amount of time and material wasted would be maximized.  The solution?  Add an edge bevel; significantly less steep than the face, making it both easier to manage, less time consuming to sharpen, and MUCH stronger, since there is more material immediately behind the cutting edge.  It is not uncommon to add more sets of bevels and microbevels, all less acute than the last.  A less acute edge is not going to be sharper, it is going to be stronger, because of the wider angle(and it helps remove wire edges, but that’s another can of worms).

The word ‘sharp’ itself only denotes that something “has an edge or point that is able to cut or pierce something”(as defined by Google), but the word ‘strong’ denotes something that is able “to move heavy weights or perform other physically demanding tasks”(also Google).  If we want a tool to cut or pierce something, we need a sharp edge.  If we want the tool to cut or pierce in spite of great opposition, we need a strong edge.

In the world of cutlery, there is nothing quite like a sword.  A giant hunk of metal had to be tamed into a weapon that is at once life-saving and life-threatening, with an edge strong enough to deflect a lethal blow, and sharp enough to inflict one.  If there is any other knife quite as demanding to be found, it is surely in the hands of a cook.  It is not a mistake that professional kitchens are depicted as steam- and stress-filled bunkers, where food is a beloved but war-torn homeland, and the line is the foxhole in the back keeping the diners at bay, only you are sweating, swearing and suffering to get them to stay.  The home cook is typically focused on getting to the meal, and the raw ingredients only stand in the way of impressing a first date or, worse yet, satisfying the roulette-wheel tastes of a toddler.  A great knife is going to get you through that prep time, so you can focus on the food.  The knife is your tool, but the enemy of the knife is it’s companion—the cutting board.

No other knife is designed to be so constantly battered as a kitchen knife.  We demand that they withstand acidic lemons and deboning chickens, hacking the board over and over through onion after onion, and yet still politely chiffonade basil for us.  A great board is nice to an edge, but there’s no two ways about it—a kitchen knife is designed to be bashed into a piece of hardwood, plastic, or rubber over and over and over.  We do not want another thing to keep up with in the house and in professional kitchens, a knife that stops working will ruin days and cost you money.  This is another reason the edge needs to be strong!

A strong edge will be durable, because there are only two ways a knife loses it’s edge—it either bends, or breaks.  The softer steels will bend and flop back and forth, being happily brought back to life with a careful hone on a rod, and the hard steels will cut for a long time until they get tiny little chips and dents that need a bit of stropping to cover up and/or replace.  But eventually, stropping won’t remove all the microscopic chipping, and honing with a rod will only flop that edge back and forth until snaps off like a tab on a soda can. By increasing the amount of steel directly behind the cutting edge, you are offering more heft to a softer steel(think a V8 tab), and a stronger structure on a hard steel(think mountains, not skyscrapers).  Your edge will be able to bash into that board a little while longer with some extra backing.

The reason this can be achieved—the real magic behind sharpening—is because sharp does not mean “acute”.  The given definition for sharp was simply “able” to cut or pierce, and no matter what the angle, this is a function of how well the two planes meet each other.  If you machine a square steel block down to perfect square, the edges would surely cut you, though they are bulky 90degree angles.  The edge that takes up such a tiny amount of space that it delivers all the weight and momentum onto a very tiny spot—so tiny that the object being cut just can’t help but to get out of the way.

There are, of course, exceptions to the “perfect edge” scenario, such as very elastic or temperamental foods like tomatoes, chicken skin, or Uramaki covered in cling wrap.  For this, you need sheer friction and grabbing power, as provided by edge teeth.  Teeth are enough of a subject to deserve an article to themselves, so I won’t bother to go into great detail here, but they deserve mentioning, because teeth do not offer a substitute for a strong, well-formed edge.  Teeth that are placed on an irregular edge are going to cause a world of trouble.  Imagine using a chain saw that had all different teeth on it, large and small, and pointing every direction; it would be suicide to use a machine like that, and though it won’t kill you, it doesn’t make any more sense to put a sloppy toothy edge on a kitchen knife and call it a day.

As hobbyists, it is easy to get caught up in the “perfect edge” race, trying to make a super acute cutting edge that will magically fall through food under it’s own dainty weight.  But these edges never last, and when you start to cook, grab a knife, and demand that it work, that kind of edge offers nothing extra in return for a much higher investment in putting it there.  The food we cut with our knives is not demanding—not when compared to things like cardboard, nylon rope, young tree branches, horns, and(at one time, anyways) chainmail.  We are taking something that was made of metals from around the globe into a space-age steel alloy, hammered and heated, cut and ground, painstakingly heated and cooled, ground some more, cleverly designed, finished and perfected, then personalized by ourselves on often rare and valued sharpening stones…and pushing it through a carrot.  It’s a no contest.

An edge bevel is not put there to make a knife sharp, it exists to make a knife strong.

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