Naniwa Fine 220 Grit Japanese Dressing/Flattening Stone, Grooved, 17cm X 5.5cm X 3cm
Over time, any sharpening stone will start to wear and the surface will become hollowed out somewhat, and so it will need to be flattened (also sometimes referred to dressing or lapping). This stone is made for this purpose. Just wet the flattening stone, wet the sharpening stone, and move the flattening stone over the surface of the sharpening stone until you have it level to your liking.
Warranty: 90-year warranty against manufacturing defects.