The 400 grit Naniwa Super Stone is a coarse stone perfect for grinding a new edge on your knife, and working out nicks or cracks or other imperfections. Use this grade only when you regular maintenance and finishing isn't doing the trick anymore as it's quite coarse and will remove metal quite aggressively and quickly. Naniwa Super Stones are reliable, forgiving and not fragile so are a great choice for a whetstone beginner. All Naniwa S2 Super Stones are made with a resin bond. Resin bonded Super Stones don't require soaking in water prior to use, a splash of water is enough. After using the whetstone, rinse and wipe off the residue. Store out of direct sunlight. Do NOT place in a dishwasher or store in a cold place. Gentle drying and room temperature storage is recommended.