Ceramic knife sharpening

Status
Not open for further replies.
C

crafty

Joined
Jan 15, 2010
Messages
212
About two years ago a received a set of (cheap) ceramic knives from a friend. Was curious about them and played a little with them, but soon they ended somewhere in a cupboard… just because they were dull. Now and then I’ve tried to sharpen them, but didn’t get really satisfying results. Normally I consider my knives to be sharp when I can shave the hairs of my arm, but I never get to this state with the ceramic knives (even got ZDP shaving sharp).

As suggested in the forums I’ve tried to sharpen them with diamond stones (300/400/600) and also with sandpaper (I’ve got up to 2500x). Probably I just have to spend much longer on sharpening them, but I’m curious how sharp people got theirs.

I know off course that ceramic knives are much harder to sharpen, but I’m curious if people got their ceramic knives shaving sharp? And how?
 
Extract from sharpening made easy

"Diamond stones will sharpen a ceramic knife, but you must remove all scratches caused by the diamonds. Scratches act as stress risers and can cause the brittle ceramic blade to fracture.

Silicon carbide wheels or stones can be used to sharpen ceramic knives, which are made of relatively softer aluminum oxide. Since paper wheels use silicon carbide abrasive, they too can sharpen ceramic knives. SC wheels can also remove the scratches from sharpening with diamonds.

Ceramic blades will not raise a burr. You have to use the other tests to determine if you have created a new edge."

I suspect you've probably gone through the grades of diamond too quickly. You probably need to inspect the edge with a jewellers loupe or linen tester to see when to move up to the next grit, or use a magic marker (use one that can wash off) on the edge to see how you're going.
 
I understand that the white ceramic blades are Zirconia (Zirconium oxide), and the black blades are Zirconium carbide. Both of these materials are harder than Silicon carbide. ZrC is supposed to be the next hardest substance after diamonds. I bought a Kyocera battery powered ceramic blade sharpener. It uses diamond wheels. I haven't had to use it yet. Just getting ready.
 
parbajtor said:
I suspect you've probably gone through the grades of diamond too quickly.
Click to expand...

That's my guess as well. I've used the marker trick too. Unfortunately no paper wheels here, I just have to do it by hand... So I'll need a little extra patience.

But I'm curious if someone got it shaving sharp :)


I've had a Kyocera diamond (hand) sharpener, just like this. But that was really a piece of crap. Probably the battery powered ones are better. Well I just stick to my diamond stones.
 
Last edited:
i have a boker ceramic that was sent to me dull as a butterknife. now it has a good working edge. i think if i would spend a little more time i could get the knife a lot sharper than i have it now. i used some super fine diamond disks that i use in my dremel tool. the edge i have on the knife right now will cut anything i need to cut just fine. since it does what i want it to to, i doubt i need it any sharper.

i have been using the paper wheels for the past 20 years and i have not tried them to sharpne a ceramic blade yet but i think i need to give it a try. the way i look at it , if a ceramic blade can do what i need it to do without it being "shaving sharp" then that should be good enough. i have never seen a tomato or anything else that needed a shave :D
 
Last edited:
Not all ceramics are created equal, so I'd assume there would be a lot of different answers, depending on the individual blade. The 'ceramic' term refers more to the process of creating them (heating to very high temps, and cooling), but doesn't indicate or imply the elemental composition of the material itself. Even simple clay pottery is considered a ceramic material (in fact, the word 'ceramic' originates from the Greek word for 'pottery'). It may be that some 'ceramic' materials can be sharpened by SiC or AlOx, but not necessarily others. Both SiC and AlOx are types of 'ceramic' materials themselves. I'd bet the newer ceramic knives, anyway, are likely harder/tougher than older versions.

The one common precaution I've heard, with regard to sharpening ceramic blades, is that very fine grit only should be used. Coarser grits of diamond, or whatever, are known to increase the risk of chipping the edge which, as mentioned earlier, can lead to cracks or major fractures of the blade itself.
 
Last edited:
Almost all modern ceramic knives are made of zirconium oxide (zirconia). This is becasue zirconia has very special properties that allow it to be toughened against crack-propagation.

If you want to read about how ceramic knives (and hammers) are toughened, it's described in one chapter of this wonderful popular-science book (highly recommended!):
http://www.amazon.com/Why-Things-Break-Understanding-World/dp/1400048834/ref=tmm_pap_title_0

tl;dr version:
Some materials can exist in multiple forms: For example, carbon can be either diamond or graphite. These different forms are called polymorphs and/or allotropes (see wikipedia for details). It turns out zirconia has multiple forms which engineers have learned how to manipulate (by chemistry and processing). Basically, the zirconia in knives has two forms, a high density form, and a low density form. The knife is engineered by material science to trap some of the zirconia in the high-density form. When a crack hits a particle of the high-density zirconia, it expands by changing into the low-density form. That is, it literally squeezes the crack shut (at the very tip of the crack). This makes it harder for the crack to continue growing.

Other ceramics may be engineerable in this way (I don't know). But zirconia is the most common ceramic that is used for this. So almost all ceramic knives are zirconia based. (There are some other types of ceramics used in knives. I think Cer-Met from Boker is a different type of ceramic? Not sure.)

btw, I've been trying to sharpen a ceramic knife, and I have found it to be very difficult to do. It has a working edge, no problem. But I would like to get it to hair whittling, which I haven't been able to do. It seems the very edge of the knife easily chips and crumbles during sharpening. If you find a nice way to get a zirconia knife to hair-whittling sharpness, please do tell! :)

Sincerely,
--Lagrangian

-------------------------------------------------------------
"What grit sharpens the mind?"--Zen Sharpening Koan
 
Last edited:
I've been running into the same thing myself on a Boker, actually. Even with the 1k WEPS paddles and the lightest pressure I can manage, I can't get it to shave armhair. Looking at the edge under the scope shoes that the edge looks like a tiny little bread knife, just constant, even-sized chips across pretty much the entire edge.
 
A hair-whittling edge on a ceramic knife might not be so good anyway, save for bragging purposes. I'd be worried about making the edge so thin that chipping might be an issue under normal use. There was a thread posted a while back, with a video link of somebody 'evaluating' a ceramic kitchen knife (an 'inexpensive' one), and the knife actually fractured while cutting food, with big chunks of the ceramic coming off. Seemed as if the edge was especially vulnerable to chipping if/when the blade was deep in some tough vegetable, or perhaps in not-quite-thawed meat/poultry. Torque/twist the blade a little sideways, and pieces of the edge break off. In that particular case, the knife was brand-new, straight out of the box.

Edit:
Found that thread. The knife was a 'Yoshi Blade' (cheap, 'As seen on TV' type of quality). The video is linked in post #18 of this thread ---> http://www.bladeforums.com/forums/showthread.php/837462-Ceramic-kitchen-knife-how-to-sharpen
 
Last edited:
It should be possible to get a ceramic knife to hair-whittling sharpness. At least, it is sharp enough for sushi-chefs in Japan.

Clip from BBC Documentary (also on Discovery Channel I think):
Show name: How do they do it?
Footage from: Kyocera's factory in Japan.
http://www.youtube.com/watch?v=GT9nElKJj5o&feature=related

The video is slightly misleading, because they confuse strength and toughness, and they don't mention that there are materials which are harder than zirconia (other than diamond). But otherwise, more ore less OK.

Another somewhat-interesting clip, where they interview one of the guys at Kyocera who sharpens ceramic knives:
http://www.youtube.com/watch?v=Oqn7vcByIgo

Sincerely,
--Lagrangian

-------------------------------------------------------------
"What grit sharpens the mind?"--Zen Sharpening Koan
 
Ceramic blades are not at all easy to sharpen and not something you can really do by hand on a stone. The wear resistance is far too high and freehand is not a option because the angle control needs to be much better than that. The proper equipment is expensive but you can find 650 mesh 1x30 diamond belts for a fair price if you look.

Good luck.
 
@knifenut1013:
In the second video I posted (http://www.youtube.com/watch?v=Oqn7vcByIgo), the sharpener at Kyocera does freehand sharpening on a mechanized grinding wheel, and later a grinding disc (it's about 1:15 into the video). I'm sure the abrasive is some kind of diamond grit. He then finishes on some kind of green buffer/polisher thing. It looks like green compound, but I have no idea if it is chrome oxide or not.

Since all his sharpening is hand-held, I think working freehand can have precise enough angle control.

Sincerely,
--Lagrangian
 
On a stone.

The repeated strokes needed on a stone would vary too much. Though still freehand on the wet grinders the ability to cut the bevel on the first pass makes a big difference unlike a benchstone where you would repeatedly remove and replace the blade on the hone
 
Komitadjie said:
I've been running into the same thing myself on a Boker, actually. Even with the 1k WEPS paddles and the lightest pressure I can manage, I can't get it to shave armhair. Looking at the edge under the scope shoes that the edge looks like a tiny little bread knife, just constant, even-sized chips across pretty much the entire edge.
Click to expand...
the ceramic knife i have is a boker also but i have yet to really look at the edge under magnification to see what it looks like. i might have to try the paper grit wheel again and keep checking the edge and see what that does. a grit that breaks down as you use it might be what is needed to work down the little chips to get a finer edge.

i bet your knife will cut like crazy just like the one i have even though it will not shave hair. a buddy had his heavy duty tow strap tied to the bumper of his jeep and it broke right at the bumper. it was a tight knot and he tried to get it untied but gave up. he never tried to cut it so i decided to try the ceramic knife on it. the ceramic blade went right through it as if it were cotton rope.
 
knifenut1013 said:
On a stone.

The repeated strokes needed on a stone would vary too much. Though still freehand on the wet grinders the ability to cut the bevel on the first pass makes a big difference unlike a benchstone where you would repeatedly remove and replace the blade on the hone
Click to expand...

But with a guided system (on a benchstone or EdgePro-system) it should be possible then...
Still curious if someone can make their ceramic knife shave.
If it's useful...? well maybe Gillette or Wilkinson can make razors with ceramic blades so they remain sharp for a longer period :D
 
richard j said:
...i bet your knife will cut like crazy just like the one i have even though it will not shave hair. a buddy had his heavy duty tow strap tied to the bumper of his jeep and it broke right at the bumper. it was a tight knot and he tried to get it untied but gave up. he never tried to cut it so i decided to try the ceramic knife on it. the ceramic blade went right through it as if it were cotton rope.
Click to expand...

No question there, Richard, it DOES cut. Just not nearly as smoothly or as evenly as I would really like it to. I've got a couple more things I'm going to try, I think... The problem is finding an abrasive hard enough to grind the stuff! Diamond is about where it's at.
 
The Kyocera diamond sharpener has two diamond wheels inside which are spring loaded against the blade. There is one angled slot for each side of the blade. The motor runs on 4 AA batteries. The guide housing is reversible so lefties can use the gizmo. I can't wait for my ceramic knives to get dull so I can try this thing out.
 
Komitadjie said:
No question there, Richard, it DOES cut. Just not nearly as smoothly or as evenly as I would really like it to. I've got a couple more things I'm going to try, I think... The problem is finding an abrasive hard enough to grind the stuff! Diamond is about where it's at.
Click to expand...
the one i have almost push cuts paper. will yours do that?
 
Status
Not open for further replies.
Back
Top