Will a knife with a polished edge cut a tomato?

[Mark76]

There is a debate on the question whether a knife with a highly polished edge will cut a tomato easily. Some people contend that in order to penetrate the skin of the tomato, the edge should be toothy. A highly polished edge will slip off the skin, so they say.

One of them is Eamon Burke and to show his argument, he made the following video. (Go to 03:10 for the scene where he tries to cut a tomato using a knife with a highly polished edge.)

However, according to Smokeeater, a knife with a highly polished edge actually cuts a tomato better than a knife with a toothy edge. He made a video as well. (Go to 04:20 for the scene where he tries to cut a tomato using a knife with a highly polished edge.)

Smokeater shows that a knife with a highly polished edge easily cuts a tomato. Eamon shows it doesn’t. Who is right?

I decided to try for myself. I took my Konosuke petty, which has a blade of AEB-L, my favorite stainless steel. I sharpened it at 12 degrees with my Shapton stones and finished at 16K. That is what I call a polished edge.

Then I tried to slice a tomato.

Eamon, what the heck did you do to your edge?

(By the way, this is my first YouTube video ever :cheer: . I also posted this on my blog, Molecule Polishing[/url]. My first post in almost two years :ohmy: .)

Molecule Polishing: my blog about sharpening with the Wicked Edge

[tcmeyer]

I suspect the difference is the included angle of the edge. Without actually having tested it to prove my hypothesis, I’m guessing that an acute angle – say 25 to 30 degrees – will slice through a tomato easily, while a more obtuse angle – 40 degrees? – may not.

In my experience, a 40 degree toothy edge (especially a microbevel) will cut flesh (meat) easily while a polished edge at the same angle will not. Here the temperature of the meat is also important. Very cold meat will cut more easily than warmer, softer meat. I suspect that the slipperiness of the surface is also a contributor and maybe related to the temperature.

I’ve also seen the same effect when cutting hemp or nylon rope. Again, the slipperiness of the material surface is a contributing factor.

[Mark76]

You’re probably right, Tom. Maybe the quality of the steel is also a factor. (Though I don’t think it is a factor for this. For example, soft German steels definitely profit less from high-grit stones than hard Japanese steels, but that doesn’t mean they don’t benefit at all from this.)

I’ve promised my little nephew to sharpen his Victorinox knife next Sunday. I know he’s already looking forward to what uncle Mark will do with his knife, but he doesn’t know I intend to sharpen it to 16K Shapton 🙂 . He’ll be very happy with the result and I’ll see how a soft German steel sharpened at 44 degrees will handle a tomato :cheer: .

Molecule Polishing: my blog about sharpening with the Wicked Edge

[Aaron kimpton]

I have polished a number of my knives, down to 1 micron with leather straps at 15dps. They most certainly cut tomatoes. I am betting he rounded over the edge when polishing it.

[CliffCurry]

I have a young chef in training coming by the shop tomorrow for a special sharpening before he flys all the way to New York for a cooking job interview.

Im gonna let him have his choice of toothy or polished & will try to post a video of in kitchen testing as we progress…

[Josh]

Great post mark thanks!

As Tom pointed out, imho edge geometry has a TON to do to with it, as does a proper burr free apex. One thing you will notice is that neither of them used a scale when cutting to show the force used to be sure there wasn’t any bias on the force applied. They also did not discuss the edge geometry (I did skip a little bit of the video, so maybe they did and I just missed it).

In Eamon’s video you notice that there was probably an issue w/ the highly polished edge that was sharpened when he said it will shave “pretty well” – a highly polished edge sharpened properly should be able to shave extremely well, like shave your face well.

Smokeeaters video wasn’t all that fair either because who is to say the factory edge was even satisfactory? In my experience, Shirogorov are sharpened to about 22-24 dps, an extremely thick angle, and it could have been blunted from the factory. He should have sharpened that one on the Wicked Edge w/ a 400-600 grit stone, no stropping and he would have noticed a marked difference.

What I have noticed over the years is this – thin edges excel at high polishes whereas thicker edges excel at coarser grit. But there are also other factors to take into account… such things as Cliff Stamp have noted like: coarser edges having longer edge retention than finer grit edges, You can also see that in general, when using coarser edges on soft material they do excel. My argument would be – design the knife for the intended use. Will you be push cutting mostly or slicing? The chef in the below video does a ton of push cutting so he needs a super thin highly polished edge. Tailor it to your needs… 😉

It’s funny they posted on this on Cliff’s forum and here are a few interesting videos:

[Mark76]

I sharpened my nephews Victorinox today. And man, I’ve seldom seen him so glad. He’s cut up quite a few sheets of printer paper 🙂 .

I also tested the knife on some tomatoes. I had sharpened it at 22 degrees. Now this small knife isn’t ideal for tomatoes, but I could do some testing. Which was in one way rather inconclusive. I used Smokeeaters method and after 1000 grit it was hard for me to notice differences anymore. I got the impression that the more polished, the better the knife cut, but that could be my prejudice. Anyway, the main thing is that also a blade with soft steel sharpened at a low angle cuts tomatoes well when having a highly polished edge.

I have a young chef in training coming by the shop tomorrow for a special sharpening before he flys all the way to New York for a cooking job interview.

Im gonna let him have his choice of toothy or polished & will try to post a video of in kitchen testing as we progress…

That should be fun 🙂 . When I sharpened for a restaurant, I was in for some surprises when I let them choose what edge the wanted. I found out it’s highly personal.

What I have noticed over the years is this – thin edges excel at high polishes whereas thicker edges excel at coarser grit. But there are also other factors to take into account… such things as Cliff Stamp have noted like: coarser edges having longer edge retention than finer grit edges, You can also see that in general, when using coarser edges on soft material they do excel. My argument would be – design the knife for the intended use. Will you be push cutting mostly or slicing? The chef in the below video does a ton of push cutting so he needs a super thin highly polished edge. Tailor it to your needs… 😉

Good points, Josh. Do you know if Cliff (or anyone else) has written any articles on the phenomenon that coarser edges having longer edge retention than finer grit edges? I can makes this out from some of the results he has posted (like the ones you linked to), but I haven’t found any full article on this. Maybe it’s there, I sometimes have a bit of trouble finding things there.

Molecule Polishing: my blog about sharpening with the Wicked Edge

[Josh]

Good points, Josh. Do you know if Cliff (or anyone else) has written any articles on the phenomenon that coarser edges having longer edge retention than finer grit edges? I can makes this out from some of the results he has posted (like the ones you linked to), but I haven’t found any full article on this. Maybe it’s there, I sometimes have a bit of trouble finding things there.

Sure Mark! This article he wrote stems from the research done in that post… if you scroll to the bottom you can find the relevant links.

[Mark76]

Thanks!

Molecule Polishing: my blog about sharpening with the Wicked Edge

[CliffCurry]

I have a young chef in training coming by the shop tomorrow for a special sharpening before he flys all the way to New York for a cooking job interview.

Im gonna let him have his choice of toothy or polished & will try to post a video of in kitchen testing as we progress…

Follow up, no video was taken due to time shortage. We did do some testing but after the first knife sliced a grape so paper thin you could see through it the testing stopped and devolved into just ohhhs & awwws of amazement by all.

Things to remember when sharing the sharpening experience with newbies…most people have never seen anything this sharp before & some people tend to get nervous when you run your thumb down a sharp blade to test 😛

I must say it was a highlight moment with several enthusiasts and huddled around watching and asking questions as I applied the various tools of the trade, they especially like the usb scope of the edge under magnification. B)

[Leo Barr]

I picked this up from a clip of a Katana polished preping the. Lads to hand over to the owner he did 1 honing pass on each side of the blade with a relativle low grit stone so now I do this on most of the knives I do generally one light pass each side with a naniwa cholera 600 grit it is just enough to make the edge bite .

[Author]

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