A shot of the Kyocera OK-45 alongside a Martha Stewart Chef's knife and Japanese utility knife :
The OK-45 ceramic utility kitchen knife blade is 0.075" thick and 1.1 inches wide and weighs a mere 60 grams. The primary grind is about a half an inch wide (0.54) and is sabre-flat on one side, dual flat on other side, another flat grind goes from the middle up to the spine. The edge is very thin, 0.005-0.010" behind the edge bevel and sharpened at a decently acute angle, 19.5 (9) degrees per side. The edge is uniformly polished along its length. The blade will push cut photocopy paper straight down, and can scrape shave a little. It has a synthetic (blue) handle with an ergonomic shape and lightly textured surface.
Push cutting 3/8" hemp required 31 (1) on a push cut through the tip with no aggression on a draw. The force increased to 36 (1) lbs near the base of the blade where the edge was slightly thicker.
The knife was used mainly compared to a Henckels paring knife which had been modified previously to increase its cutting ability by about 100% over the new in box profile. The edge of the paring knife was currently 0.011" thick by 0.051" wide, 6.2 degrees per side. It has a slight micro-bevel of 22 degrees per side either with a fine ceramic (less than 5 micron grit) or a 600 grit DMT finish depending on what is being prepared. When sharpening, the edge on the paring knife burrs readily as the steel is soft and therefore weak and thus it is necessary to go very light on the rods to avoid burring it heavily.
Giving the Henckels a fresh sharpening to a fine push shaving finish with a fine ceramic rod, it easily push cuts right into photocopy paper same as the ceramic blade. On the thread the paring knife took 148 +/- 13 g, and on the poly it was 0.060 +/- 0.04 cm. Thus, the ceramic was just as sharp near the base of the blade, but slightly blunter as you run out towards the tip. The cutting ability is very close between the two as well as demonstrated cutting the hemp. The Henckels takes 32 - 24 lbs (base to tip), on the hemp with a push cut, and 20 +/- 1 lbs on a two inch slice. So the Henckels does cut the rope a little easier near the tip of the blade, and is significantly more aggressive with a slicing action.
It needs to be clarified here that the Henckels doesn't well represent optimal sharpness for steel, due to the low hardness, the edge is difficult to refine it past a certain level. As an illustration, a MEUK made by Allen Blade in 52100 steel heat treated by Ed Caffrey, which has an edge between 0.005 - 0.010" thick and ground at ~15 degrees per side, when finished on 0.5 micron CrO buffing compound was significantly sharper than the Henckels. The MEUK only took 115 +/- 11 g on the thread, and a minimal 0.50 +/- 0.07 cm on the poly. An overview of the sharpness of the freshly sharpened blades :
|Knife||Thread (g)||Poly (cm)|
|OK-45||135-205||0.75 - 1.4|
|Henckels||148 (13)||0.60 (0.04)|
|MEUK||115 (11)||0.50 (0.07)|
As a stock test I used the three knives to each perform 250 cuts through freshly picked rhubarb. All blades could cut the rhubarb well when it was layed out flat. With each blade, a simple draw cut severed the vegetation easily. The higher initial sharpness of the MEUK made no practical difference cutting this specific material in this manner. However when the rhubarb was stacked and thus the cuts had to go much deeper, the MEUK actually fell significantly behind as a lot of pressure had to be applied to force it through the vegetable. The much greater stock thickness of the MEUK was for this cutting more critical than the high initial sharpness. It should be pointed out that for this type of draw cutting a more coarse finish is actually better. A cheap paring knife I had on hand with a 600 grit DMT finish easily out sliced all three blades. After the cutting the sharpness was measured again. An overview of the sharpness of the used knives :
|Knife||Thread (g)||Poly (cm)|
|OK-45||200 ( 5)||0.95 (0.11)|
|Henckels||190 (12)||0.75 (0.06)|
|MEUK||205 ( 5)||1.10 (0.07)|
Now the Henckels shaved the best followed by the OK-45. The MEUK could not shave at all, not even scrape any hair from my arm. All blades could still push cut photocopy paper at a ~45 degree angle. The extensive blunting of the MEUK is most probably due to a combination of the high force required which tended to make it hit the cutting board harder and corrosion. The MEUK took a visible patina during the cutting (rhubarb is acidic). The edge on the MEUK had several damaged spots up to 0.002" deep, and extensive smaller ones. The Henckels only had one small damaged area about 0.001" in size, and the OK-45 was unaffected except for one spot 0.002" deep by about 0.02" cm long .
The ceramic utility knife was then used for several weeks in the kitchen cutting along side other blades to gauge its abilities in a subjective manner to get a feel for its performance. The sharpness was enough to cut most materials very well, alongside the better steel blades I had which had with fine polishes using the ceramic rod usually. Breads, meats (including trimming fat), vegetables and fruits were no problem for the ceramic knife. I thought the greasy fat would be a problem, but it was cut very cleanly and efficiently. The sharpness of the ceramic was also retained through several sharpenings of various steel knives, so the edge retention is indeed many to one over steel knives. However it should be noted that with the use of a smooth steel (or fine ceramic or diamond rod), the sharpness of a steel knife can be maintained to a very high level with less than a minutes work at the start of the day.
There were however a few foods that the higher sharpness of some of the steel knives did induce greater performance, slicing potatoes for example. The softer the material, the more sharpness will come into play into overall performance. There were also some foods that the ceramic knife did not cut well at all such as tomatoes, plums and basically anything with a tough skin which was soft underneath. If the fruits were fresh, and thus semi-rigid, the knife could handle them ok. However if they were at all a little soft, then this bit of give would prevent any cutting and the blade just skated over the skin unless excessive force was used which just mashed the foods. Really hard crusty breads were also a problem, the edge would tend to just skate over the crust. Of course a steel knife with a high polish won't cut any of this well either, the breads or the fruits. For those foods you want either a serrated knife or a steel one with a coarse finish. A 600 grit DMT rod gives enough aggression for most of these problem foods as do the common butchers steels.
As an interesting side note, after a session of heavy cutting with the ceramic blade I noted that the edge had rolled significantly and would only shave on one side. About eight hours later when I went to measure the sharpness I found that the shaving ability had returned to both sides and it was back at the factory level again. I would have tended to think it was just my imagination however I have quantified this with steel blades, but this is the first time I have seen it with a ceramic. This is a well known property of straight razors, and why it is often suggested that you have at least two and use them in rotation.
This knife has a very ergonomic and comfortable handle. I much preferred it to the squarish grip on the Henckels. It is also very light and thus generates no fatigue no matter how it is gripped. Using it for many tasks which generally sees a paring knife (peeling potatoes), the OK-45 did them all well and was easy to handle. Not having to rinse a knife after cutting acidic vegetables could be a serious advantage to some. The only real serious problem is the low durability. It can't be used for bone cutting, even light work such as splitting a chicken, which the Henckels paring knife will handle with just some edge flattening. However it easily handles all other cutting and doesn't demand a light tough, the OK-45 held up fine rocking through some thick turnips for example.
The blade didn't dull significantly during the above described use, however after reading some comments on the web about touching up ceramic knives on ceramic rods, specifically the Sharpmaker from Spyderco, the blade was given a couple of passes on the same fine ceramic rod used in the above. The edge got broken apart for the entire length showing chips from 0.002"- 0.004" deep. A 600 grit diamond rod improved the finish, but left it many times rougher than it would a steel blade. It seemed logical that the rods were exerting too much pressure on the edge so a 1200 grit DMT pad was used which significantly improved the finish. Interestingly, checking the edge under magnification, it is multiple times as coarse as it would be on a steel blade.
With the 1200 DMT finish, the knife can just slice paper. It is much duller than the NIB condition, and takes 600+ g to cut the thread. The slicing aggression was also low, not being able to cut tomatoes as it did when NIB. The edge doesn't seem to take micro teeth like steel blades do when left with a rough finish. The ceramic may breaking apart at the edge whereas the steel knives are getting cut and thus the structure of the edges are very different, you would want high magnification to check this out (100-1000X).
Using silicon carbide sandpaper on cardboard (the cardboard has some give which increase angle sharpening tolerances) the blade was honed at various grits. The sandpaper came in 240, 320 and 400 grit, and there was enough of it to make 28 of the strips for each grit, which were about 2 cm wide and 6 cm long. After each session of honing the sharpness was tested cutting paper a few ways, slicing up a roll of 100% cotton (the sleeve of a shirt), and checking it under magnification to see how the edge behaved. The "hones" were not wore out after the session, so that package of sandpaper had enough material for more than 50 honing sessions (more than one lifetime for one blade).
Using the 240 grit strip and ten passes per side edge trailing, and then 10 per side alternating the edge was full of chips of up 1mm deep [x20 mag]. The blade didn't see any increase in paper slicing ability, it could only slice photocopy paper at an angle, and tight to the point at which I was holding it. On the fabric, it took two complete passes of the blade using heavy pressure. For comparison, when freshly sharpened it only took about 25% of the blade to make a complete cut. The blade virtually would go right though the fabric almost in a press cutting motion.
Onto the 320 grit strip, the edge was given 20 strokes per side and then 10 per side alternating, the chips were now cut in half. The paper slicing ability took a huge jump as it cuts very smooth on an angle, and could cut straight down on a slice but needed a tight close grip, about a half and inch or so from the edge contact to where the paper was held fixed. The fabric slicing ability also took a huge jump and now only needed about 3/4 of the blade length.
The 400 grit paper was then used for the same amount of honing. The edge now went back to having similar chips as in the 240 grit honing, and were more frequent. However the paper slicing ability got smoother again, and the fabric was down to needing about half a blade length. Using some fifteen micron SiC paper from Lee Valley, didn't improve the cutting ability, but the finish changed. The edge got smoother overall, the chips were cut in half and the frequency much reduced.
Finishing with some five micron SiC paper, also bought from Lee Valley, used for the same number of honing passes, the edge finish got a little smoother under magnification. The paper slicing ability went up significantly and now the blade was approaching the ability to push cut straight down, start a cut on a draw and then turn it into a smooth push. The fabric was now only taking about 25% percent of the blade length and was approaching a push cut. The edge was now also just barely starting to shave.
Using the OK-45 on carrots, meats and the like and the performance was very high, easily in the same class as what you could expect from production steel knives, and easily sharp enough to cut any food with the exception of things like over ripe tomatoes.
A strip of 0.5 micron CrO paper was used for subsequent honing and the OK-45 gained shaving ability rapidly. After a few sessions of 20 passes per side, it could shave decently well (this was just on a section of the edge to speed things up, there is a huge jump from 5 micron SiC to 0.5 micron CrO which slows the honing down). The blade was now cutting the paper very smooth, with no loss of fabric slicing ability. The edge was approaching a smooth straight line under the scope.
As a check on the sandpaper quality a a steel blade (TAC-11) was ran through the same process as the OK-45. The edge on the TAC-11 improved in a smoother manner as the grits were progressed through. The steel blade was also much sharper at any given grit than the ceramic. After the five micron paper it was shaving quite smoothly.
In short, 400 grit SiC sandpaper, which you can find almost anywhere, will put an above average edge on the ceramic blade and thus there is no requirement for expensive or hard to find hones. This edge can be refined with higher grit sandpaper, the automotive section of most hardware stores will carry it up to 2000 grit. To get the finest shaving edge, just as with steel blades, you will want to finish with CrO. Based on the fact that the CrO will sharpen it, it seems likely that waterstones might work as well.
The largest problem with sharpening ceramic knives is that many of the common tools won't work. For example steels which are commonly used on kitchen knives will either do nothing (smooth ones), or break the edge apart (grooved or butcher steels). The Spyderco Sharpmaker and v-rod or "cats eye" kits will also just damage the edge. The ceramic versions will just break the edge apart, and the diamond ones while they will sharpen the blade, induce a lot of micro-chipping due to the high pressure and thus are not really effective solutions. However the blades can be sharpened without undo difficulty using quality Silicon Carbide (SiC) sandpaper which is available at hardware and craft stores.
However the edge does not respond well to coarse finishes. With steel blades an edge sharpened with a coarse hone is a very aggressive slicer for use on crusty breads and other hard to slice materials. The ceramic blade did not behave this way at all, so it is not as versatile in regards to types of finishes. However it does have a rather large advantage which is that it does not, unlike steels, form a "burr" or "wire edge". This simplifies the sharpening process and removes one of the more frustrating elements.
In regards to time, ceramic is much harder to machine than steel, however when sharpening you only have to remove very little material, it is on the order of microns, and this will happen with very little time. Using the above sandpaper the knife went from a very dull state to a very sharp one in just a matter of minutes. Kyocera also ships the knife with a very thin edge so there is little area that you have to hone which also greatly decreases sharpening time. The initial edge is also very sharp and even which means that your first sharpening effort is not wasted cleaning up a poor factory edge.
So overall for sharpenability I would give the knife and average rating as the advantages and disadvantages balance each other out. However if I was someone who relied on v-rod setups or extensive use of steeling, the rating would be much lower.
Considering that this is a light use knife, it might be worthwhile to try a more acute edge geometry, maybe even a chisel edge Japanese style profile to increase the cutting ability.
The initial sharpness was better than average for a blade of this price, steel ones included. The overall cutting ability was far better than production western cutlery and approaches the highly efficient Japanese blades. The handle ergonomics are very good, it is comfortable in a variety of grips, no sharp corners and large enough to fill the hand nicely. The security is better that average as many production knives have slick hard plastic grips and the Kyocera has slight dimpling. The corrosion resistance is of course excellent. The durability is very low when compared to steel knives. As for sharpening, well that is average as described in the above.
|Cutting ability||very good|
|Handle ergonomics||very good|
|Ease of sharpening||Average|
To clarify on the durability. If this knife is used in the manner described by Kyocera, cutting soft foods and handling with care then you will have no problems. It showed no actual signs of use let alone any problems with breakage after weeks of kitchen use. If you can avoid hard objects like bone, not use the knife as a scraper, and in general avoid banging it around, I don't see any breakage problems being likely. However I used the rating of dismal as they are meant to be relative terms which should place the knife in regards to its completion. When you consider what else is commonly used, the ceramic blade is a lot less tough than the common soft production steel knives which can take a lot more pounding. It is common around here to see knives get thrown into drawers with other knives, dropped into sinks with dishes etc. . The ceramic blade would react badly to this, whereas something like a Henckels will take only minor edge blunting which can easily be steeled out.
You can comment on this review by dropping me an email : cliffstamp[REMOVE]@cutleryscience.com or by posting in the following thread on Bladeforums :
|Last updated :||Tue Jun 17 10:18:33 NDT 2003|
|Tue Sep 24 15:39:24 NDT 2002|