How Honing Really Fixes Knives (A Correction) (Patreon)

Hi everyone,

I wanted to take a quick moment to correct something I said in my latest knife-sharpening video.

In that video, I repeated a very common explanation of the difference between sharpening and honing: Sharpening on a whetstone removes metal, while honing on a honing rod merely realigns a rolled edge back into its original shape.

This is the explanation I was taught everywhere from other restaurant cooks and chefs, to my fellow editors and test cooks at Cook’s Illustrated and Serious Eats. It’s one of those things I’ve repeated so many times that I’ve never really considered that it may be incorrect.

So when a number of folks in the comments pointed out that research exists proving that honing does, in fact, remove metal from the blade, I went back and did some reading, particularly from an excellent website called Science of Sharp. The author has done a huge number of experiments using a scanning electron microscope to look at blade edges before and after sharpening, stropping, honing, and actual use.

And unlike a lot of discussions about knife sharpening—which can very quickly turn into people repeating things they’ve heard from somebody else—here you can actually look at the edge and see what happened to it.

It turns out that I was incorrect: Honing absolutely removes material from the blade, and in retrospect it seems almost obviously true.

How a Knife Dulls

If you are interested in knives, razors, sharpening stones, honing, stropping, abrasives, or just looking at extremely tiny pieces of steel, Science of Sharp is an incredible resource and rabbit hole to get lost in, and I urge you all to go there for the full picture, but for now I’ll offer a summary based on their research. There’s one article in particular called What Does Steeling Do? Part 1 that directly tests the idea that a honing steel simply realigns a rolled edge.

The first interesting thing is to look at what a dull knife edge actually looks like. The mental image I’ve always had—and the one I’ve presented in books and videos—is basically a very thin piece of steel that has flopped over sideways, bending, kinking, and rolling so that the sharpest bit of the edge (the apex) does not align with the direction of pressure. 

According to the microscopy, this is a thing that can happen, but it’s not the main way in which knives become dull through ordinary use.

A mushroom-shaped dull apex. Photo via Science of Sharp.

But according to the microscopy in Science of Sharp, it’s not necessarily the main way that knives become dull in ordinary use. In fact, there are a wide range of ways in which a knife tip can get dull. It can wear away through abrasion from cutting tough foods or repeatedly rubbing against the board. It can develop microscopic chips (or in the worst cases, visible chips) that make cutting rougher and increase friction. In some images, the malleable metal apex even gets deformed into an almost blunt mushroom-like cross-section at the apex.

What Does Honing Do?

None of these issues are ones that can be solved simply by “re-aligning” the apex and, in fact, what the author found was that in most cases, the work being done by the honing rod was not simply realigning existing metal, it was actually removing material at the microscopic apex to create a brand new cutting edge—one with a shallower angle than the edge the blade was originally sharpened to.

A cleanly rolled apex. Photo via Science of Sharp.

To further drive home the point, the author did another useful experiment. His goal was to test the effect of a honing steel on a blade that is simply rolled without any abrasions, chips, or major deformities. To do this, he used a glass beaker to push the apex of a knife blade sideways until it was visibly deflected, with a cleanly rolled edge you can see with the scanning electron microscope.

If there is any truth to the idea that a honing rod works by re-aligning a rolled knife edge, then honing this rolled blade should see the knife end back in close to its original state.

A freshly honed apex shown against a white outline of the original knife blade, proving that material has been removed to achieve a newly keen edge. Photo via Science of Sharp.

Instead, after using a normal ribbed honing steel, the edge is sharp again. And, instead of the original rolled edge simply standing back up, material has been removed from it, essentially creating a micro-bevel at the tip visible to the microscope but not your eye.

But wait. It goes deeper.

When Does Honing Actually Deform?

There’s a second article called What Does Steeling Do? Part 2: The Card Scraper which I think makes the whole thing even more nuanced.

If you’ve ever done woodworking by hand, you’re probably familiar with a card scraper. It’s a card made of soft metal that a woodworker will deliberately deform the edge of in order to create a little burr. This burred card can then be used to scrape the surface of wood creating a burnished finish that is smoother than anything you can achieve with sandpaper.

Looking at one of these cards that was very gently bent under the microscope confirms that indeed with light pressure, the steel bends and gets reshaped through plastic deformation, losing very little material in the process.

A card scraper edge showing the deformation as well as material removal. Photo via Science of Sharp.

However, as pressure increases to the point where it’s strong enough to create a properly-functioning burr on the card scraper, there is a combination of both deformation as well as material removal at the very tip. Turns out this is a good thing, as that material removal is what makes the very apex of the scraper—or the apex of a honed chef’s knife—actually feel sharp.

The Conclusion

The author’s conclusion is that burnishing can involve both moving steel and removing steel, depending on the pressure and the geometry involved.

So I think the final correction I would make to my previous explanation is this:

A honing steel can absolutely bend, burnish, or realign some deformed steel, but it is not accurate to say that honing merely realigns an edge while sharpening removes metal. Honing also removes metal, and in the normal maintenance of a kitchen knife, a large part of what a honing rod appears to be doing is removing a very small amount of damaged steel and creating or refreshing a microscopic bevel right at the apex. This appears to be true of ribbed steel rods, ceramic rods, and smooth steel rods.

There’s still a very useful distinction between honing and sharpening, and that largely comes down to scale. Sharpening on a stone works on a relatively large portion of the bevel. You are grinding steel away to thin the blade and recreate the overall geometry of the edge.

Honing works at a much smaller scale, doing much of the same thing, but only at the microscopic edge of the blade—the microbevel. And once you’ve used the honing rod enough times that the microbevel has been abraded or chipped past the point that it can be fixed, it’s time to pull out the whetstones.

I always love when I learn something I’ve always taken for granted is actually incorrect. It feels like a really great plot twist in a movie. The kind that makes you re-evaluate your past reading of situations and re-consider things going forward.

So thanks again to everyone who pointed me towards this really cool research, and I urge all of you to go check it out yourselves. There are a lot more amazing images and experiments to look at over there.