Sharpening is really two processes: Grinding and honing. Grinding is simply the removal of metal. Honing is a precision abrasion process in which a relatively small amount of material is removed from the surface by the means of abrasive stones. Once you have the right shape, usually using a more aggressive grit, you then switch to a finer grit to hone the edge.
For a quick jump, you can see on the chart below made by Steve Bottorff described on his popular book Sharpening Made Easy: A Primer on Sharpening Knives and Other Edged Tools. The book tells many things about knife sharpening, sharpening system and DIY guide how to sharpen razor-sharp edges. If you want to surf deeper into the world of the sharpener, then it is one of a must-read book for you. For you who dwell in the Mainland or around the United Kingdom, you can buy the book through the link below.
A blade's sharpness may be tested by checking if it "bites"—begins to cut by being drawn across an object without pressure. Specialized sticks exist to check bite, though one can also use a soft ballpoint pen, such as the common white Bic Stic. A thumbnail may be used at the risk of a cut, or the edge of a sheet of paper. For kitchen knives, various vegetables may be used to check bite, notably carrots, tomatoes, or cucumbers. In testing in this way, any nicks are felt as obstacles.
The composition of the stone affects the sharpness of the blade (a finer grain, usually, though not always, produces sharper blades), as does the composition of the blade (some metals take and keep an edge better than others). For example, Western kitchen knives are usually made of softer steel and take an edge angle of 20–22°, while East Asian kitchen knives are traditionally of harder steel and take an edge angle of 15–18°. The Western-style kitchen knives are generally in the range of 52–58 on the Rockwell scale, which denotes the relative hardness of a material.
This coarse grit whetstone is great for prepping old and dull knives that need to be sharpened with a fine grit stone. One of my good knives edge looked like someone had tried to chop barbed wire. After ten minutes on each side of the stone, the edge was smooth and free of imperfections. After it hit the knife with the fine grit stone, I was cutting onions and apples like hot butter! I would soak this stone for 12-24 hours before using. It sucks water like a sponge. The surface needs to be damp when you sharpen.
Low Grit Stones: A sharpening stone with grit number less than a 1000 is generally used for knives and tools that are damaged. If your blade has any nicks or chips in the blade, the stones will take care of them in a jiffy! They usually have a coarse side for nicks and chips, with the other side for general sharpening. Even if the knife’s edge has become totally blunt, the stone will re-sharpen it perfectly.
However, due to limited natural deposits and extensive quarrying over the centuries, true, high quality, Japanese water stones are now few and far between and are very expensive. Thus, various companies are now producing synthetic Japanese Water Stones which generally have a more consistent composition and grit size than natural stones as well as often begin somewhat harder and thus, lasting a bit longer; not to mention being cheaper to purchase.
The video above, from the How To You YouTube channel, explains everything you need to sharpen with a whetstone at home, and the best methods for doing so. Obviously, you’ll need a whetstone (as well as a few other things), and you’ll want to work near your sink or a bucket so you have easy access to water. Fill a container with water, then soak the whetstone in it until it stops bubbling. Inspect your blades for any trouble spots, and get to sharpening using the methods and motions described in the video; making sure to check your progress as you go. We’ve talked about sharpening knives with whetstones before, but this guide is a bit more thorough and the old video has since been removed.
As you see in the pictures, it is always very important to keep same angle of about 10' to 15', which is about two coins height between the blade and the whetstone. Gently push the point you want to sharpen with your first, second and third fingers. While keeping the angle and pushing the point with your fingers, stroke the blade until it reaches the other edge of the whetstone. Then pull the blade back until it reaches the edge of the whetstone. This back and forth is counted as one stroke. Repeat it for about five strokes until you can see or feel some small burrs (edge curvatures). Then move the position of your fingers to where you have not sharpened yet, and repeat this five strokes of sharpening processed from the tip to the base of the blade.
Meanwhile, if you want something that you can use to sharpen a variety of knives and edges, including small and pointed tools, you might want to consider the DMT WM8CX-WB 8-Inch Duo Sharp Plus Bench Stone – Coarse/Extra Coarse with Base. For less than a hundred bucks, you can even use it to repair a damaged edge because of its extra-coarse diamonds.
This set of two Norton combination waterstones provides four grits and also includes a flattening stone as an added value. The 220, 1000, 4000 and 8000 grit sides will handle everything from aggressive shaping to final polishing. They are 8" long by 3" wide, big enough to handle most knives and tools easily. Our most popular waterstone kit, this has everything you need to both sharpen with waterstones and maintain the stones themselves. A great starter set.
Clamp-style sharpening tools use a clamp with several holes with predefined angles. The stone is mounted on a rod and is pulled through these holes, so that the angle remains consistent. Another system is the crock stick setup, where two sticks are put into a plastic or wooden base to form a V shape. When the knife is pulled up the V, the angle is held so long as the blade is held perpendicular to the base. Several cutlery manufacturers now offer electric knife sharpeners with multiple stages with at least one grinding stage. These electric sharpeners are typically used in the kitchen but have the ability to sharpen blades such as pocket or tactical knives. The main benefit of using an electric sharpener is speed with many models that can complete the sharpening process in one to two minutes. The disadvantage is that the sharpening angle is fixed so some specialized knives, like a Japanese style Santoku, may need additional attention to sharpen to the ideal angle.
Now you may wonder, if a finer stone produces a better cutting edge why do I need a coarse stone at all? The answer is that finer stones work much more slowly than coarse ones. The amount of metal a fine stone removes with each pass is much less than what a coarse stone removes. If you have an edge with a good shape to it from a coarse stone, this is not a problem because the fine stone doesn’t have to remove much metal to improve the edge. If the edge is dull, it will take many times longer to reshape it with a fine stone than it would with a coarse one.