Is My Knife Sharp?
The Meaning of Sharpness: What do we mean when we say that we want our knives to be sharp? Seems like a silly question. We all know what sharp is. Or do we? Sharpness is not just a super-thin edge that will readily shave the hair on your arm; it is also a function of shape and intended purpose. You could grind your chef's knife to razor thinness, but the edge would crumble the first time you hit a bone or tried to hammer your way through a winter squash. Your knife would be sharp but useless. Similarly, a razor sharp but wedge-thick edge is great on a splitting axe but not much good for tomatoes. We have to take into consideration the shape of the blade, the angle of the edge bevel, and especially the items being cut when we consider how to sharpen our kitchen knives. So the real question is not "how sharp should my knife be," but rather "how do I get maximum performance from my knife?"
The Myth of Thick Edges: The theory is that thick edges (larger angles) last longer than thin edges, and the majority of the knife-buying public wants the edge to last as long as possible. But it doesn't work out that way in practice. Thinner edges actually outlast thicker edges almost all the time. The thinner edge starts out performing better than the thicker edge. So even if it does degrade it has a lot of ground to lose before it falls to the performance level of the thick edge. Thinner edges cut more easily, putting less stress on the edge. If a thin edge takes three slices to get through a big slab of raw meat, a thicker edge might take six or seven. Or three with a lot more force. The thicker edge is doing twice as much work, degrading twice as quickly.
A Test for Sharpness: One way to test the sharpness of your knife is to press the edge lightly on your thumbnail at about a 30-degree angle. DO NOT PULL OR PUSH THE KNIFE TO CUT!!! If the knife cuts "grab" onto your nail, it is sharp. If it slips, it is dull. The sharper the blade, the smaller you can make the angle before it slips. Try this with a new razor blade to see how a really sharp blade feels. The down side of thumbnail testing is that the little cuts in your nail get dirty and look bad until the nail grows out. For this reason some people do this test using a plastic pen or pencil.