How to Sharpen a Japanese Deba Knife

The Japanese Deba Knife is mostly used for cutting fish. It's thick stout blade is optimised for cutting and/or crushing through fish bones and skulls with ease.
A good Deba knife has a “Hamaguri” or Clam shaped edge so you need to sharpen specific areas differently to maintain its correct cutting geometry.

Firstly the “Shinogi”, sometimes referred to as the ridge line or lamination line. This area is where the two steels ( a soft steel/iron and a hard steel ) meet.

Then you will need to sharpen the main edge or “Hasaki” and the “Kiriba” or Blade path.

1,Sharpen the rounded edge of the blade 

The state where the blade is no longer sharp is when the edge is rounded.
In order to correct this, the blade is sharpened with a medium abrasive stone at a 45 degree angle until the edge of the blade is rounded.
At this stage, any spills or misshapen edges should be fixed.

When the blade is sharpened standing up, a two-stage edge is formed at the tip of the blade.
Use this two-stage blade as the standard for sharpening.

2, Erase the two-stage blade with a rough abrasive stone.

The two-stage blade that was just attached is sharpened with a rough abrasive stone until it disappears.
If the entire cutting edge is not sharpened evenly, it will lose its shape.

At this time, it is important to note that Japanese kitchen knives (except Honyaki) are a combination of steel and soft iron.
The cutting edge is also 2/3 of soft iron. If you try to sharpen it with a uniform force, only the soft iron part will be sharpened and the shine line will be broken.
Press the blade against the whetstone with the fingers of your left hand, and apply force to the cutting edge with your right hand, fighting with each other to sharpen the entire cutting edge.

3, Attach the blade with a medium grindstone.

The surface of a cutting edge sharpened with a rough abrasive stone is very rough.
Use a medium grit stone to polish it until the scratches disappear.
Since the blade is thin, it is easy to get bounce and the blade will decrease.

From this point on, the blade will be attached in earnest.
As with the rough grind, set up the blade with medium abrasive stone and lightly pull out the small edge.
Then, sharpen with medium abrasive until this small edge disappears.

To sharpen a deba knife, sharpen it from the half of the cutting edge to the cutting edge.
This will create a rounded edge on the cutting edge.
Sharpen the blade firmly until the two-stage edge disappears.

As mentioned above, the ideal way to sharpen a de-bade kitchen knife is to change the thickness of the cutting edge and the base of the blade.
When you become accustomed to sharpening, you can sharpen the cutting edge a little wider and the base a little narrower.
When you are sharpening the edge of the blade, you should sharpen it a little narrower to make it more like a clam-shaped blade.

4,Sharpening with a finishing stone.

In order to improve the sharpness of the blade, it is sharpened with a finishing stone.
The first step is to polish the scratches made by the medium grinding stone on the entire cutting edge with the finishing stone.
Do not sharpen until you get a return.

Lightly pull out the small blade with the finishing stone in the same way as during medium sharpening.
Continue sharpening until this small edge disappears.
When sharpening with the finishing stone, be more conscious of the cutting edge than when sharpening with the medium abrasive stone.

5,Press the back side.

The back side of the knife is sharpened to get rid of the Burr that appear when the cutting edge is sharpened.
The back of a Japanese kitchen knife is concave (Urasuki), so it is easy to hit the cutting edge.
You can use only a finishing stone.

Please switch to your left hand and place the entire back side against the grinding stone.
Be sure to place the entire back side of the blade on the grinding wheel, and do not raise the blade to create an angle.
Be sure to use a horizontal grinding wheel when back-pressing.

6,Attach the smaller edge (thread edge).

At this point, the cutting edge is already attached.
However, the blade edge is too thin and is prone to spilling. The use of a deba knife in particular is rough, so be sure to do a smaller edge pull.

Use a finishing stone.
If you use a medium grindstone, the smaller edge will become too thick and the sharpness will deteriorate.
Set the blade upright at about 45 degrees and lightly sharpen the entire edge of the blade until it starts to burr.
After that, press the back side of the blade in the same way as in [5].