How to Sharpen a Japanese Usuba Knife
An Usuba is a traditional Japanese single edged, thin bladed kitchen knife.
There are a few varieties across Japan but the basic use and design is the same.
The Usuba is popular for use with vegetables and creating ornate designs with clean, precise peeling cuts, such as “Katsuramuki.”
1. Sharpen the rounded edge of the blade.
In the first step, angle the blade at 45 degrees and sharpen on a medium grit whetstone, being careful to maintain an even distribution of pressure and control.
The blade on an Usuba is incredibly thin and you can very quickly grind too much away, so extra care is needed.
Use the thumb of your right hand to maintain control at the rear of the blade, and the two fingers of your left hand on the blade edge.
At this point, rest the blade on its edge and continue sharpening.
This will create a two-stepped blade edge. This is to recreate the blades original geometry and remove burring.
2. Remove the two-stepped edge with a rough whetstone.
After the two step edge is made, remove it by sharpening on a rough abrasive stone/whetstone.
Your goal is to flatten the surface area, making it as uniform as possible. Keep the entire edge even.
It's important to note that Japanese kitchen knives (except Honyaki) are a combination of steel and soft iron.
Approximately two-thirds of the cutting edge is made up of soft iron. If you try to sharpen the cutting edge uniformly, only the soft iron part will be sharpened and your shinogi line will be broken, disrupting your knife shape.
Press the blade against the whetstone with the fingers of your left hand, and apply force to the cutting edge with your right hand. Do this with similar force from both hands to sharpen the entire cutting edge.
Don’t over sharpen, and don’t try to sharpen the entire surface of the blade!
First, start by sharpening half of the cutting edge.
After that, you can even out the entire edge (below the shinogi/ridge line)
3. Switch to a medium whetstone.
The surface will be rough after the last sharpening, so switch to a medium whetstone (finer than your last stone at least) to remove scratches and polish.
Again, as the blade is thin it’s very easy to over sharpen, so be very careful throughout the process.
The sharpening thus far, has essentially been preparation of the blade for the true sharpening process.
Using a medium whetstone, begin slowly drawing back the blade over the stone.
Pay careful attention to your angle and pressure application.
These blades are thin and easy to chip or damage, resetting or ruining your hard work.
In truth, Usuba knives often do have a slight curve, however compared to other Japanese knives, they are fairly straight and flat.
4. Sharpening with a finishing stone.
Now, you can move on to using a finishing stone.
First remove the scratches made by the medium stone on the entire cutting surface.
Lightly pull out a small edge with the finishing wheel in the same way as during medium sharpening.
Here you will sharpen the edge as a “hamaguri” or clam-shaped style, so be mindful of your angles.
A burr will appear on the opposite side which you will remove later.
5. Uraoshi, back of the blade.
You will now remove the burr using a finishing stone. The steel is now even thinner than before, so a finishing stone is generally all that is needed here.
Lay the back of the blade flat against the stone, left hand controlling via the handle and thumb on the lower portion of the blade. Right hand on the upper portion of the blade.
The blade itself should be pointing to the upper right.
Keep the blade flat and smoothly sharpen away the burr.
6. Thickening the edge.
At this point, the blade is ready to cut, but the edge is too thin and could roll or chip easily.
Use a fine finishing stone. If you use a medium whetstone, the edge will become too thin.
Return it to a 45-degree angle and sharpen again lightly until a slight burr occurs.
Finally, enjoy your knife!