Whetstone 24x3.5x1.5 cm 180grit (corundum) A whetstone 180 grit from extremely hard corundum is generally the easiest to use and most immediately effective way for sharpening of kitchen knives, garden tools and other tools.It is recommended to soak the whetstone in cold, clean water for about 10 minutes before use to prevent the surface from being clogged with metal particles. Do not wash in a dishwasher.