Once in a while depending on the usage of the knife you have to use a grinding stone to sharpen the cutting edges of the blade. At least once in a year you have to use a grinding stone to do this. By using a grinding stone you get a new cutting edge. It is better to do this grinding from a professional. If you have a sand wheel then you can also do that yourself. Some of the grinders have different types of stones that can be used for grinding. The surface of the stone varies from coarsest to fine. You have to grind your knife on all these to get the exact finishing on the edges. Some people use wet stone to sharpen their knives. Such people believe that the minute shavings from the metal keep floating from the surface so that you get better edges when you grind the knife blade. Some people are against the wet grinding since they believe that the wetness clogs the pores of the grinding stone and spoils it forever.