The Atoma #140 is the most effective sharpening stone we have tried.
It is a honing stone and coarse whetstone in one that is used to flatten uneven whetstones or repair rough nicks and damage to knives.

We use this daily to clean and straighten our Naniwa whetstones after each sharpening to keep them flat.

Can be used under running water for optimal results.

The sharpening stone is of very high quality and will last a long time.

Made in Japan

Specifications:

• Roughness (Grit): #140
  
• Type: Diamond stone / flattening stone
• Size: 210 x 70 x 11 mm
• Material: Aluminium, steel, diamond

Instructions for use

Dressing grindstones:
Place the whetstone you want to flatten on a holder, preferably in a sink with running water. Hold the Atoma #140 with both hands and rub it in circular motions against the stone you want to flatten until it is flat.
Tip: Draw a cross pattern all over the whetstone with a marker. When the marker is completely gone, the stone is flat and nice.

Repairing rough nicks/broken tips:
Add water little by little as needed to keep the stone from drying out during grinding. Grind gently on the stone with light pressure. Diamonds are very effective at removing material.
Rinse and let dry at room temperature after use.