Fun fact: whetstones are not named after the water used to lubricate the stones. The word ‘whet’ means to sharpen a blade. The process of using a sharpening stone is called ‘stoning’.
Start by submerging the whetstone in water for 10 to 15 minutes. When no more little air bubbles appear, the stone has absorbed the optimum amount of water. Now you need to flatten the stones. This is important: if your whetstone is not completely flat, it can ruin your expensive sushi knife!
Flattening whetstones is done with a flattening stone or lapping plate (a coarse, flat stone used to flatten other stones). Draw a grid or a number of mark lines with a pencil on the whetstone. Start rubbing the whetstone by moving it against the flattening stone back and forth. Continue rubbing until the pencil marks are gone. This indicates that the whetstone is flat and ready for use.
Place the whetstone on a non-slippery surface or put it in a whetstone holder. First use the low grit side of the stone. Move the blade back and forth across the entire stone with light pressure at an angle of 10 to 15˚ (roughly the height of the little finger of an adult).
Start at the tip of the blade. Slightly lift the handle. Pull the blade over the stone through to the middle and down to the base of the blade. Repeat this several times. Turn the knife around and work on the other side of the blade. Don’t press the knife hard against the stone, but let it glide over the stone.
Do each side twice for 5 minutes. So the whole process should take 20 minutes. Watch the video on the right to see how it’s done.
Note: some Japanese knives are only sharpened on one side only. If you are sharpening such a knife, do not sharpen the flat side. Rather lay it flat on the stone to remove any curling metal ‘burr’.
Repeat the above process for the same amount of time using the high grit side of the whetstone. This will make your knife really sharp.
Here are 4 simple methods to test the sharpness of your sushi knife.
I recommend a low grit between F1000 and F3000 for grinding down the metal and sharpening the knife. To finish the sharpening (polishing) I recommend a high grit between F5000 and F10,000.