Sharp, lightweight and rust-proof, ceramic knives hold their edge longer than a typical steel knife, but they're brittle. If you take good care of a ceramic knife and use it only on items it's best for, you may go years without dulling the blade. When you do, the ceramic knife requires special care -- not just any old manual sharpener does the trick. Some ceramic knife sellers offer lifetime sharpening.
Rinse the surface of the blade with a solution of mild dish detergent and clean water, then carefully scrub it clean and dry it with a soft, lint-free cloth. This helps remove any food or residue, making the sharpening process more effective.
Choose the appropriate sharpener. For ceramic blades, you need a slot-style electric knife sharpener, ideally a model specially made for ceramic. In any case, the sharpener should feature a diamond grinding disc or a diamond abrasive belt rated at about 180 grit.
Place the sharpener on a solid, level surface and turn the sharpener on -- typically you'll hold down a button on the side. Insert the blade into the sharpener's left or right slot so that the heel, the part nearest handle, is covered first. Smoothly pull the handle back toward you so the entire edge of the blade -- from heel to tip -- slowly through the slot. Use a slight "up and out" motion to ensure that the tip gets sharpened -- and raise the handle as the point comes out of the slot.
Repeat the process about three to five times in one slot, then about three to five times in the opposing slot to ensure that the blade gets an evenly sharpened edge on both sides. Test the knife on a piece of fresh fruit or a fresh veggie. If necessary, repeat the sharpening process -- again, sharpening an equal amount on both sides -- one more time.