Sharpness is defined by the quality of the intersection of the two bevels which meet at the cutting edge of a blade. That is, the steepness of the angle where the beveled edges meet should be as close to zero as possible.
The sharp blade has a zero degree radius where both edges of the bevel meet.
The blunt blade has a rounded point where both edges of the bevel meet.
Traditionally western knives have been sharpened using steels, however the main function of a steel is to realign a blade (take the bends out) to make it cut better. The Japanese use sharpening stones to bevel the edge of a knife, with the aim of producing a zero radius join where the two beveled edges meet. Sharpening is therefore concerned with the precise abrasion of the two beveled edges.
The sharpening stones come in an array of grit sizes, and just like sanding a piece of wood, starting with a larger grit and moving to finer grits allows an extremely sharp edge to be formed.
Sharpening with waterstones (or wetstones)
This method, which is suitable for both knives and tools, has the following advantages:
- The composition and hardness of the steel does not deteriorate, as there is no heat generated
- As the stones are inflexible, exact cutting edges and angles can be produced (no rounded bevels as with felt or rubber disks)
- The large array of grit sizes allow extremely fine cutting edges
- There is no risk of flying sparks (like a metal disk)
- Our wetstones are available with an inexpensive sharpening guide which ensures a 15 degree blade angle. This makes sharpening simple for even the most reluctant beginner.
The following video provides a step by step guide for using a sharpening stone.
Step by step on sharpening with a water stone (or wet stone)
- Put the stone on a firm place on top of a wet cloth or, alternatively, a base to hold the stone (you can buy these or you can make one with a stopper and wooden board and pop it inside a plastic try with low sides).
- Apply water to the top of the stone
- Hold the stone at a 15 degree angle on the 500 grit stone. Move each side of the blade on an angle for the length of the stone. Complete say, 30 rubs on one side and then repeat the same on the other side. The number of rubs or passes you do will depend on how much sharpening your knife needs. To help you keep the knife at 15 degrees you can purchase an inexpensive sharpening guide.
- For a one side beveled blade; sharpen the beveled side and simply remove the metal on the flat side by placing the blade flat against the stone.
- To test the sharpness of the blade, try cutting a piece of paper; or a soft fleshed fruit or vegetable. Don't try it out on anything hard like cardboard else you will ruin the fine edge you have just created. Kitchen knives are not utility knives. They are for cutting food.
The final sharpness of a blade also depends on the following factors:
- The molecular structure of the steel (the finer and harder the sharper)
- The cutting edge geometry (the smaller the cutting angle, the sharper (less resistance)
- The grit of the stone (the finer the grit, the sharper the result)
- The skill level of the sharpener (practice makes perfect - although our sharpening guide makes the job a lot easier)
Wetstones - hard or soft bond?
We stock both of the Shapton (Japanese) ranges of hard and soft bond wetstones.
The hard bond wetstones are more abrasive and what is required for the early stages of sharpening a kitchen knife or tool blade up to a #3,000 grit..
The choice between a hard or soft bond is only relevant when honing or polishing (that is, the last stages) to really refine your blade edge. As a result, the soft bond wetstones only apply to the #4000, #6000 and #8000 grits because they are the ones you normally use for honing and polishing. They are made to be used with when honing and polishing high carbon steels commonly known as blue or white paper steel because they offer less resistance and they wash much easier in case they glaze. We recommend the soft bond westones for honing and polishing the Tadafusa kitchen knives.
Honing and polishing with hard bond (HR) stones are largely designed for harder steels (with less carbon and more alloys) as they are more abrasive.