A serrated knife is commonly used for slicing through bread. Every so often, the blade needs to be sharpened, or it will begin to shred or tear rather than slice through food. But, due to the serrated knife design--one side of the blade being flat, the other with points and valleys--it is the most difficult type of blade to sharpen. Sharpen this type of knife only when necessary--when you notice the blade becoming dull in spots.
Lay the serrated knife blade, teeth side down, on a ceramic or marble slab.
Hold the handle blade with one hand, and with your free hand sharpen the flat edge of knife by stroking each spot two or three times, using a serrated diamond sharpener.
Turn knife over, with flat side of the blade laying against the slab.
Sharpen the serrated side with the knife sharpener by doing two or three short strokes between teeth. Do not touch the teeth with the sharpener; sharpen only the valleys between.