A master craftsman said,
“a key point to sharpen knives are to use flat waterstones.”

You cannot sharpen knives well with dented waterstones. However, it is unavoidable that waterstones to be dented as you sharpen knives with them. Because you cannot use a waterstone completely equally, its surface become unflat.

You need to flatten such a waterstone by the flattening stones. This process is the key to sharpen knives well and efficiently.

flattening stone variations

Customer reviews of flattening stones. (Quotes from Amazon.co.jp)

  • I was surprised to sharpen my knife with waterstone which I flattened with flattening stone. The waterstone sharpened my knife so sharp that I quit buying new knife.
  • It flattened my waterstone completely flat within several minutes. I became to be able to sharpen my knife effectively. I should’ve got this earlier.
  • Although I couldn’t see dent in my waterstone surface, I found it actually dented using this flattening stone. It makes great difference in sharpening efficiency to use flat waterstone or not.

Point of choosing flattening stones

Lower grit waterstones tend to be dented easier because they are realtively soft. Higher grit waterstones, on the other hand, are hard to be dented.

In other words, rough stones easily become unflat, and finishing stones are hard to become unflat. Medium stones are in-between.

Unflattening Process

Sharpening Process

1. Mark your stone with pencil

Draw striped or check pattern on the surface of your waterstone. (Fig.1)

Also, soak both waterstone and flattening stone into water and make them wet.

mark waterstone for preparing flattening


2. Rub the waterstone surface with flattening stone

As you rub with flattening stone, you’ll find some lines are disappeared whilst the other lines remain. Area where lines disappeared were protruded, therefore the other area still have pencil lines. (Fig.2)

halfway of waterstone flattening process


3. Keep grinding the waterstone surface until all lines disappear

When all the lines disappear, flat surface is recovered in your waterstone. (Fig.3)

completion of waterstone flattening process


4. Wash waterstone and flattening stone

Wash stones well with water and dry up. Now it’s ready to sharpen your knives! (Fig.4)


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