Atoma Diamond Sharpening Stone - #400_1


Atoma Diamond Sharpening Stone - #400


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Atoma Diamond sharpening stone from Japanese manufacturer Tsuboman with granulation #400 grit is a standard diamond plate for flattening sharpening whetstones and to repair damaged blades. It removes material very quickly (both from whetstones and when repairing knives), works very well with all types of steel. It is crucial in the knife sharpening process that your whetstones are always flat, as it will preserve the life of your stones and ensure accurate and efficient sharpening. Always splash some water on the diamond stone before sharpening.

Excessive force should not be used when sharpening with Atoma diamond stones as this can remove diamonds from the plate, which, when pressed roughly, can loosen, thus destroying the surface of the plate.

One of the main arguments why diamond sharpening stone works so well is that it is completely flat and does not deform/hollow when used. On the surface of the stone are exclusively monocrystalline diamonds which are more expensive than polycrystalline, but much more durable. They are bonded to the plate by the electrolytic process.

Diamond stones can be compared to sandpaper in structure - both have a thin layer of abrasive surface attached to a non-abrasive base. Of course, the lifespan of the two is not comparable - the diamond will last much longer. Initially, the surface will be extremely rough/sharp, followed by a long period of medium roughness which will eventually wear off. While this diamond stone is sold with a 10mm thick aluminum base (glued to the diamond plate), a replacement #400 grit plate can be purchased separately when the original wears off.

Dimensions (LxWxH): 210 x 75 x 11.5mm (8.3" x 3" x 0.45")


  • For stone flattening - secure the whetstone that needs to be flattened with a stone holder. Placing the diamond stone on top of the whetstone, use circular and up-and-down movements to begin flattening process. For better results, draw a grid on the whetstone with a ballpoint pen or a pencil (do not use markers, those can be absorbed into the surface of the stone). When the grid is no longer visible, the stone is flattened. Thoroughly rinse both stones to remove any excess material. Flattening whetstones to up to #5000 grit will get you good results by only using the Atoma diamond stone, while for higher granulations we recommend finishing with the Nagura - dressing stone to get a smoother/finer surface on the whetstone. 
  • For knife repairs - place the diamond stone on a flat surface and make sure it won't move around (use a stone holder for the most secure position). Proceed with the same movement/sharpening technique as with whetstones to fix a damaged blade (see our Knife Sharpening Guide for details).

Advantages of diamond sharpening stones:

  • quickly removes material when repairing or changing the blade's geometry
  • quick sanding and straightening
  • can be used for sharpening very hard powder steels (ZDP-189, HAP-40, R2)
  • it retains its shape and does not deform (become hollow) with use
  • lower granulations (#140 and #400 grit) are excellent for flattening whetstones

Disadvantages of diamond sharpening stones:

  • for a really fine/smooth edge and for very precise sharpening, whetstones are a much better choice - diamond stones are too rough
  • not suitable for making "kasumi (mirror) finish" on the blade

Tip no.1: When flattening stones, one should never forget the edges of the stone. In the process of flattening, we create sharp edges that need to be smoothed out at the end. Sharp edges of the whetstone are fragile and can damage the blade of the knife while sharpening.

Tip no.2: Once done with flattening, rinse the whetstone and diamond plate thoroughly under running water to remove any material residue. For better results, use a (tooth)brush or sponge, but do not try to clean the diamond plate with your fingers, it is not very pleasant (tested and not recommended 😊).

Tip no.3: If you want to reduce the number of stones in your sharpening set, Atoma #400 can also serve as your base stone from which you can then proceed to #1000 grit whetstone and higher granulations. At the same time, you can also use it as flattening stone.


Beginner's Guide to Knife Sharpening

Knife Sharpening Guide

If you are new to knife sharpening, then don't skip on our Beginner's Guide to Knife Sharpening. We cover all the basics and teach you how to properly sharpen a kitchen knife.

Discover expert tips, techniques, and product recommendations in our sharpening blog posts to sharpen your knives like a pro!

Read Our Sharpening Blog

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