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Kiwami Japan
A popular Youtube channel called “kiwami japan” includes several videos of making knives out of unusual materials such as jello, pasta, chocolate, etc. The video on making a knife out of cardboard has over 20 million views which means that these videos have reached a broader audience than just knife makers or enthusiasts. As a materials engineer I find the videos interesting from a materials perspective, but they are entertaining in other ways as well. The videos are a bit quirky so I decided to take a dive into these videos and try to figure out what is going on. I also e-mailed the person who makes the videos and he answered a few of my questions. I will refer to him as “Kiwami” for the rest of this article though I know that is not his name. Kiwami means extreme in Japanese.
The person making these YouTube videos hides his identity. I think for the true fans there might be some small reflections to use to piece together what he looks like (I don’t have that much time), but in general he either doesn’t show his face, or covers it up. He also rarely speaks and many of the videos include only the sounds of whatever he is working on:
That GIF of him holding a sickle is perhaps more menacing than the channel appears, in general. He often uses subtle humor in the videos such as being expressive with his hands:
Or by adding anthropomorphic elements to materials he is working on:
Or by showing how much time has lapsed in a project which is taking a particularly long time:
His videos started out with making various things with cheap materials, like “I made a karambit knife with a sickle” or “I made a Nunchaku with 4 dollars.” The first knife video was the karambit, and he followed it up with a video of making a butterfly knife. The making of knife videos started to ramp up with “Manually repair very rusty Japan’s $500 kitchen knife.” That video got many more views than those he had made previously and it appears he wanted to capitalize on what was a popular topic. Indeed, when I asked him how he became interested in knives, he said, “I am not interested in knives…Since the video of the knife is popular at YOUTUBE I am making a knife.” His next video was “Sharpening a $1 Kitchen knife with $300 Whetstone.” And indeed he does have some very nice waterstones, from coarse diamond stones up to a 30000 grit Shapton Pro, which is the $300 stone in question.
The next shift in topic that he made is the one that brings us to this article, and that is using his waterstones to produce knives out of various odd materials, the first of which with “the World’s hardest food.” This was a video of making a knife out of dried bonito, which he states “holds the Guinness record for world’s hardest food.” I haven’t checked him on that but I will take his word for it. He used a food slicer and a file to make the knife followed by waterstones to sharpen it. He demonstrated its sharpness by cutting paper and its durability by puncturing a can:
A somewhat similar pattern is shown in the rest of his videos, using hand tools like files, hand operated drills, and sharpening stones to produce the knives. He often demonstrates extreme patience in producing the knives. Much more patience than I have. I asked him why he doesn’t use any power tools and he said, “The material I make is very weak. Power tools can destroy materials.” He began producing many of these videos with making knives out of different materials. He usually names them with “sharpest ____ kitchen knife in the world” hence the title of this article. Starting with the chocolate knife, the majority of them use the same design as the $1 kitchen knife that he sharpened with the expensive water stones.
While many of the knives are relatively simple in terms of material selection, such as making a knife out of hardwood, some are more complicated. With many of the materials some preparation is necessary such as grinding, baking out liquid, melting, etc. Some creativity is definitely necessary to get “plastic bottles” or “underwear” to work as a knife material. In a few cases he has to “cheat” by adding other things to make the material work. For example, in the “sharpest smoke kitchen knife in the world,” he collects soot from burning candles and then mixes it with rawhide. So even though the video title states that it is made from “smoke” it doesn’t just use soot but also rawhide which makes up a significant portion of the structure of the knife.
In most videos he ends it by cutting cucumber with the newly completed knife. The cucumber is often found in unusual places:
In the majority of the videos he provides a “sharpness ranking” which has somewhat unclear criteria. It appeared that it mostly correlated with hardness of the materials but I wasn’t sure. That makes sense as the hardness of the materials likely controls to what sharpness can be achieved, even with all of them being sharpened with a 30,000 grit waterstone.
That is confirmed in more recent videos where he has purchased a “Shore Durometer” hardness tester; he uses the “Type D” version. This hardness tester is typically used on hard plastics, which is probably a good range for the type of materials that he is testing.
After he started using the hardness tester he stopped providing a sharpness ranking and started providing the hardness value of each material instead.
The Shore D scale doesn’t overlap with the Rockwell C scale (see “SD” below), though there may be less reliable readings at the top end of the Shore scale (~100). Therefore in general these materials are much less hard than the steels we generally use in knives:
Hardness correlates with strength, which means that higher hardness material will resist deformation of the edges better than low hardness materials. This is easy to visualize by thinking about using a knife made of cardboard or chocolate. It is easy to imagine such a knife bending or the edge rolling. When the material is less likely to deform that also makes it more feasible to sharpen it to a fine edge, which is why I think hardness correlates strongly with his previous “sharpness” scale.
A similar though somewhat different property is “elasticity” or “elastic modulus” of the material. Cardboard, for example, will flex some before it stays permanently deformed. The resistance to flexing prior to permanent deformation is the elasticity, and elasticity does not necessarily correlate with hardness. You can read more about elasticity in this article about flexing and bending. The hardness of steel can be changed to a wide range of values but the elasticity does not change as it is controlled by the strength of the bonds between iron atoms. However, when looking at a wide range of materials elasticity does tend to correlate with hardness [1]:
Another important material property is toughness. With better toughness the knives are less likely to chip at the edge during use. Toughness often correlates with ductility, or the extent that something can be deformed before it fractures. The materials being soft relative to steel does not necessarily mean that they are also ductile. For example, styrofoam is both soft and brittle, easy to both deform and to break apart. This problem was evident in the knife made out of KFC chicken bones, as even with delicately cutting a cucumber, chips in the edge were seen:
There are other potential problems to using some of these unusual materials, of course. The ice knife and chocolate knife are likely to melt. Kiwami also told me that some of the materials are “weak in water.” The jello knife would probably eventually dissolve if left in water too long. As mentioned earlier in this article, many of the materials cannot even be worked by power tools because they will deform or fracture. However, the fun of the videos is just seeing someone successfully produce a knife out of such odd materials.
There are more complex material properties to discuss about the various choices, but would probably lead into too many directions, and there isn’t much information out there about the material properties of dried jello. For example, carbon fibers individually are strong, but are used in a composite with many fibers along with another material such as epoxy or other polymers. Because it is a composite of carbon fiber and epoxy, the hardness measurement is a composite measurement of both the epoxy and many different fibers, which is much lower than the strength of an individual fiber. When used as a knife the composite properties add up to a knife material that isn’t superior to steel.
There is some variation in how thick he makes each knife and at what angle they are sharpened. This is required to some extent by the material properties but it is not always clear how the geometry is chosen. I asked him how the thickness and edge angle is chosen but he just said, “The material I use is special. Therefore, thickness and angle vary depending on the material.” That is approximately how much I knew before his answer. I asked how many knives are made for testing out of each material before making the final video and he said he makes about “3 samples” per video.
Conclusions
I asked Kiwami if any of the materials have been as good as steel and he responded, “No, Iron and steel are better. Both hardness and elasticity are excellent.” While that may be in part because of the intentional selection of odd materials, there is a reason we use steel in knives. Steel has excellent properties in terms of hardness, elasticity, wear resistance, and toughness. It is also relatively inexpensive and there are many manufacturing facilities that already exist which were designed to produce steel knives. Perhaps it goes without saying, but steel is likely to stick around as a knife material.
[1] https://pubs.rsc.org/en/content/articlehtml/2015/tb/c4tb01267d
