Friday, March 27, 2009

Ceramic knives.

There were quite a few questions about them, after the last post. So I'll share what I know.

EXACTLY how they're made is a mystery, because it's proprietary information. The one documentary I managed to watch on the subject of industrial ceramics, when they got to the cutting implements, they toured a factory and weren't allowed in half the rooms. However, from cruising the site over at Kyocera (I notice they're also selling ceramic-based ballpoint pens... hmmm), I see they say absolutely NOTHING about how the ceramics are made. But from the properties they have, I assume they're really either ceramic/glass or ceramic/metal composite. It looks and acts more like ceramic/glass should behave (breakage), but when it comes to composite I wouldn't count entirely on that to tell you what it is. But I'm guessing some kind of high-temp ceramic/glass composite.

Anyway, the material is really hard. Harder than metal. Which is, as with most things, both a benefit and a liability. Because it's SO incredibly hard, it's incredibly brittle, and doesn't flex at all. However, the lack of flexibility makes it possible for the ceramic to hold a sharper edge than metal. These are so hard and weird that you have to send the knives back to the factory for sharpening.

See, when you sharpen a metal knife, you get to a stage where the edge is so thin it can't support itself and either folds over or rolls up on itself. So metal knives are kind of intentionally dull; after sharpening, they knock off that folded over edge (the burr). While I'm sure ceramic (and any other material) will do the same thing, the 'point of collapse' where the edge is too thin and breaks off, is far thinner than with metal. (Am I making sense? I'm more an organic, non-metallic chemistry kind of girl.) Long story short, on a molecular level, ceramic is harder and so can hold a thinner - and therefore sharper - edge.

What's this all mean in real life? They feel funny when you use them. You may not think so, but after a lifetime of using metal knives, we're all used to our knives flexing. Cheapass knives flex a LOT, but even good knives have a little bit of flex in them. It's just how metal WORKS. So you use a ceramic knife, and you notice almost immediately that it isn't flexing a damn bit. I don't know about other people, but for me it makes me handle them a bit more cautiously. The only thing I used to use my ceramic knife for (I've had one for about ten years; just not a whole block of them) was slicing. Cutting thin slices of meat, cutting thin-skinned fruits like tomatos, that kinda thing. Dicing and mincing and like that is good, too, though I find for mincing I like the rocker-shaped blade of my metal chef's knife better. Anything that leads to a knife wedged into a big chunk of food (pot roasts, watermelons, bodies) is asking for breakage. I'm told chefs use these a lot for mincing up herbs, where you need lots of 'sharp' and not any 'crush'.

They're also super-sharp, to a disturbing level. I once cut entirely through a chicken leg (including the bone) by ACCIDENT, without realizing it. I'm only half kidding about how I'll eventually lop off a finger with one of these. More than capable of handling a banana or ten.

I confess, we also have a ceramic vegetable peeler. (The Perfect Peeler at the top of the page.) The husbeast does the bulk of the potato peeling at our house, and I bought it for him last Christmas as a gag gift more than anything else, but he loved it. I've used it since then, and it is AWESOME. Smooth as a baby's butt, and the peels come right off. And it's reasonably priced and everything.

So, food for thought. Basically, like everything else, ceramic knives are great, except for when they're not. I won't be giving up my (metal) boning knife any time soon.

Damn it. Now I want the pink santoku. And if I breathe a word to the husbeast, the crazy fucker will go buy it when we've got knives coming out our ears. (Just for the record, price-wise, these are about equal to high-quality home kitchen metal knives like Henkel's. But I still don't need a pink ceramic knife.)

Ooo! Look! Henkel's has a section on knife skills!


Elly said...

Sliced through the bone? *shudder* I'm backing away now.

Carol Hoover said...

I love your post. I read you everyday. I love how you don't hold back your opinion and I find that so refreshing.

Ok, about Ceramic, I am a dental technician. I work in the high tech department where we work with Zirconia.
It is a ceramic. We design the substructure of a crown or bridge on the computer with a Cad/Cam program. They call it digital design. And then the information is sent to another computer which mills out the crown.
They have a block of zirconia which is like a soft chalky looking block. After the machine mills out the bottom it fill it with white wax, just to give support. Then the block is turned over and the mill removes more material till it has the crown or bridge. This is only the base for the crown, we will be putting porcelain on top of this structure and shaping it.
After the mill finishes the crown/bridge will go to a burn out oven to remove the wax. Then it will go into a very high degree oven for 8 or more hours to bake.
The equipment is very expensive so we don't have this in our lab. We send our computer designs to the main lab and then 3 days later they send us the crown and bridge bases.
My job was to take these zirconia bases and remove the thickness at the margins. The margin is where the edge of the crown meets the patients own tooth.
I had to use a high speed hand tool, like your dentist would use. It turned at 350,000 RPMS. It also sprayed water on the crown. If you generate heat the zirconia might crack.
Sometimes we would have an extra crown and we would try to see how hard they were. We would throw them on the floor, and stomp on them. They don't break. They do have sharp edges that cut you. The material is amazing.
When a dentist has to remove a Zirconia crown, it is very difficult.
Sorry to be so long. I just loved this subject.
Here is a URL about Zirconia.

Louiz said...

cool, but sharp, knives. Don't do what I have a habit of doing - drop them point first into your feet. Ceramics are an amazingly hard substance

Caroline said...

"Pot roasts, watermelons, BODIES"!?

You eat BODIES? o_0

MLJ1954 said...

there is nothing quite like a good knife. We have the junk knives. I have the goods knives. The kids are not allowed to use the good knives. Just like they are not allowed to use my sewing machine or my good scissors. They don't call me Queen Mom for nothin'.

Amy Lane said...

Okay, how sick is it that I'm filing this information away for a fight scene later?

Annie Robertson said...

Wow its amazing designs !
A steak knife is used for chopping vegetables, as the sharp edge of its blade is capable of delivering the brilliant performance in slicing salad & fruits.
Ceramic Scissors