Even the best blades will lose their initial sharpness over time.
Whetstones, also known as water stones or sharpening stones, are used to grind and hone the knife edges.
The KOTAI 1000/6000 Combination Whetstone offers you two grits: a fine 1000-grit side to grind away rougher edges, and an even finer 6000-grit side to put the final touch for a razor-sharp edge.
With the 2 different grits, you can conveniently keep your knives razor-sharp yourself.
Not only does this make it safer for your fingers, it will also allow you to keep the sharpening angle constant.
Soak the whetstone for 15 minutes before use (until air bubbles stop coming out of the stone).