My guess is that it could get nicked, chipped, or otherwise damaged by banging against other items. If it is your favorite knife, it is not worth risking. I do not wash any of my best knives in the DW, but most of them having wooden handles.

Ceramic knives do not have wood handles, and generally both the blade and handle are made of dishwasher safe material.

However, banging by other objects can mar the handle and chip the blade's sharp edge.

But the most important reason why no knife, any knife, should ever be in the dishwasher: If someone not realizing there is a very sharp knife in the dishwasher and reach in to get something, it can be a bloody dangerous situation.

dcarch

I do put inexpensive steak knives in the DW, but only in the silverware rack and always point down. I also only put forks with the tines pointing down. Dishwasher accidents are a fact of life, and a woman in England was killed when she fell onto her open dishwasher and landed on upturned knives.

The sharpest knives are the most dangerous, but I still put butter knives in the DW with the handles up. It is also dangerous to wash knives by hand, and I often lay them on the counter (handles hanging off) and wash the blades while they are lying flat on the counter. This is only when they have something stuck on them.

I put my best knives in the dishwasher....I lay them flat on the rack, nothing touching....and I keep any with wooden handles well oiled. Don't always put them in but I feel that it keeps cooties out of the joints by the handles and sanitizes them.

Mineralized metals are called ceramics. Iron oxide (rust) for example. as they become harder on the hardness scale, they become brittle.

I got curious, so did a lot of reading. The only ceramic blade I have is in a paddle mandoline, and I do put it in the dishwasher.

Most of the issues with putting a ceramic knife in the dishwasher are about agitation and chipping, as Dcarch said. If your DW has a sharp knife holder, I think that would take care of it. Apparently, the force of the spray can bounce them around enough to chip them if they're just laid flat. Because they're non-porous, they supposedly won't transfer flavors from one item to the next (I didn't even know that was an issue, though I do, out of principle, give a light wash or rinse to my steel knives between items that aren't going in the same pot).

With steel knives, according to what I've read, the issues for the dishwasher are that the detergent, especially the amount of sodium and the abrasives, can be bad for the blade, and that there are often aluminum bits in the handle that can corrode over time, leading to a loose handle. Also, without being in a secure spot, being bounced around so that the edge hits things (including the wires) can dull the edge.

I also learned that ceramic knives are made of zirconia oxide powder. Cool. :)

I like Lars's way of washing sharp knives. I always hold the handle when washing mine, and use a soapy sponge, if I have one, or more generally, smear a little dishsoap from back to edge, right on the blade, and let it wash and rinse under the hot water. Not the most water saving way to wash them, but they get clean and it's safe. I also use edge guards for storage.