Have you ever started slicing or chopping vegetables or meat and find your knife won't even cut soft butter? Here is a tip for you.
Turn over a plate or cup and whet your knife along the edge of the bottom where the glaze is missing. Fired porcelaine or pottery makes as fine a whet stone as the most expensive ceramic stones available today.
First stroke your knife on one side, then the other--from haft to tip--until you achieve an appropriate edge. But be careful! Your knife will now be very sharp!