Those who make bladed tools outside of Japan have developed increasingly hard metals in an attempt to keep blades sharp longer. These blades certainly cut well, but they have also become increasingly difficult to sharpen. Japanese blades differ in this respect because they have been developed under the premise that "sharpening" is not unavoidable but is actually desirable.

　For the best combination of strength and ease of sharpening, the hard steel used in Japanese blades is thinned as much as possible and softer steel is added to it. To make flat blades and planing blades easier to sharpen, the backs of the blades are designed to with a shallow concave indentation--in other words reducing the surface area that coes in contact with the sharpening stone when sharpening the flat side of the blade. Also by using "kneaded" steel, the blades become stronger and more flexible. 　

　If you don`t sharpen the blade, it will never cut.

There are two methods of sharpening--the traditional method of moving the blade along a sharpening stone by hand, and sharpening by bringing the blade in contact with a moving sharpening stone (i.e. a machine). Japanese woodcarvers have coined the phrase "three years of sharpening" because it literally took three years of sharpening the dozens of different blades every day to learn the traditional method correctly. Furthermore it required many long hours every day--not ideal for someone who wants to carve as a hobby or pastime.

　Naturally, the easier method of machine sharpening has become much more popular. But aside from the "rough sharpening," it is still best to apply less pressure for a longer period of time to avoid denting or rounding the blades. There are both natural and manmade sharpening stones, but the natural ones are very expensive; the cheaper ones contain impurities and have inconsistent qualities. On the other hand, a good-quality manmade stone can be obtained witout spending hundreds of dollars. The stones that you will need are #1000 or lower coarse stone (粗砥石) for "rough sharpening." A #1000-#2000 medium stone (中砥石)and a #5000 or finer finishing stone (仕上げ砥石).

　The coarse stone 粗砥石 is used to correct or straighten the shape of the blade. This stone is used only as needed because frequent use unnecessarily shortens the blade.

　The medium stone 中砥石 is used after the coarse stone or when there is a small defect n the blade or a spot of corrosion. But if you need to make a major correction, it is best to use a rougher stone. Using too fine of a stone tends to take too much time and the blade will likely become rounded (maruppa). Always try to use the most appropriate stone for the job.

　The finishing stone 仕上げ砥石はis used after the medium stone or when the cut of the blade seems to have dulled. Don`t use this stone immediately after the coarse stone--no matter how long you try the blade will be too roughto sharpen with this stone.

　In principle, the angle of the blade is sharpened at an acute angle with respect to the soft material and at amore obtuse angle with respect to the hard material. A blade that has become rounded means that the angle of the tip of the blade is more "obtuse" than the rest of teh body of the blade. It is called rounded because the surface of such a blade inevitably becomes curved over time. The cut of a rounded "maruppa" blade is of poor quality--the blade slips and will not bite into the wood. Sharpening a bladeliterally means thta the small particles of the stone shave off bits of the blade metal--it is obviously a reductive process. Therefore, the rougher the stone particles the deeper these particles will dig tiny "gutters" into the surface of the blade. ("gutter-like scratches and streaks" in the blade are caused by the stone partcles being dragged across the surface of the blade) Simultaneously, the "mountains" between these gutters will also become relatively taller and the surface of the blade (on a very small scale) will become wave-like. When this "saw-like" blade comes in contact with the wood, it is likely to break or at least not cut very well. Therefore it is necessary to sharpen it with as fine a stone as possible to reduce these gutters and mountains and keep the tip of the blade straight. when sharpening, you should exert pressure with the hand that holds the blade in contact with the stone not the one that holds the handle.

　If you sharpen a brand-new blade until it is almost mirror-like, the maruppa of the blade will disappear when you sharpen the front of the blade. The thin very thin metal at the very tip of the blade will bend back. but like the gutters and mountains, it will disappear when you use a fine stone. Even after the blade has become mirror-like, there are still small "gutters" and "mountains" not visible to the naked eye. so when you sharpen, always hold the blade as you wood when you carve--so that the stone`s movement is in a straight line relative to the stone. "if you sharpen it until it glitters like a mirror, it won`t cut like a knife" is a pure myth. Blades that are that well sharpened cut better than any other. When you carve "scooped out" hollows, etc. it is best if your blade is very slightly rounded.

Extra Information

　Blades have a "front" and a "back." The "front of the blade is the side with the diagonal slope and the side with the softer metal.The back of the blade is flat and is made of the harder steel. You should also sharpen the backs of new round and triangular knives beore using them.

Knife manufactures say that they sharpen the knives, but they don`t usually use the finishing stones. if you look at the tip of the blade with a 20x lens, you can see the saw-like or wave-like phenomenon described above because the "gutters" and "mountains" are cut in the same direction as the blade as sharpened. You must try to make these as small as possible if you want a sharp blade that cuts well.

Also, no matter how much you sharpen the front of the blade, you must also sharpen the back if you truly want it to cut well. If the back of the blade becomes round, it is very difficult to correct. If this happens, it is best to shorten the blade and corect it completely. Also, the kaeri of the blade will disappear if you use a fine stone. If it still occurs, you must either use a finer stone or your blade isn`t forged correctly.

if the back of the blade is completely straight and flat, a slightly rounded front will make it easier to use, but rounding it too much will cause the blade to slip--make sure you don`t injure yourself. last but not least, if you sharpen the blade in the same direction you carve--i.e. straight--the blade will stay sharp longer.