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A friend of mine bought some new, very sharp knives. He has a magnetic strip that he uses to store knives, but he does not put these new knives there because he says magnets dull knives.

Is that true? I've never heard of this. If so, why do magnets dull knives?

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The magnets themselves don't dull them; they're not nearly strong enough to deform a blade.

But it is possible to damage your knives on those racks. It's very easy to drag the blade along the rack a bit as you pull it off, and easy for the magnet to snap it against the rack as you put it on.

Both are avoidable, though. When removing the knife, you twist it so that the sharp side leaves the magnet first. When putting it on the rack, you let the blunt side touch first, so when it snaps the rest of the way on, it's only the flat side against the rack, never the blade.

It also helps to get a version that's not just bare metal; there are plenty with the magnet underneath wood. It might not be ideal if you let the blade drag along it a lot, just as you probably don't want to drag it along your cutting board, but it's a lot better than metal. Also, since the knife isn't directly against the magnet, the force doesn't increase as sharply as you get to the rack, so there's less snap.

So, if you're worried that you (or guests in your kitchen) may not always be too careful, a bare metal magnetic knife rack is definitely not a good idea. But unless you're really protective of your knives, the wooden kind is probably fine.


Folks have also pointed out that in principle, long-term use of a magnetic rack could magnetize the blade, causing it to pick up tiny bits of metal, especially during sharpening, which would then wear and dull the blade. As far as I know, this is not a big deal: I've seen knives stored long-term on magnetic blocks without noticeable magnetization. You could always keep an eye out and demagnetize the blade if necessary.

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    Mine is home made: I embedded rare earth magnets on the side of the cabinet, and then covered the area with friction tape. Besides preventing it (a big Chinese knife) from sliding down, it cushins the pointy part. And the side is wood, anyway. – JDługosz Mar 20 '17 at 10:31
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    There is some belief that the magnets also slowly magnetize the knives which and cause them to slowly reform at a low level and dull. I am not a big believer, but if true this would tend to effect cheaper and thinner, and especially unhardened blades more. If true. – dlb Mar 20 '17 at 14:33
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    @dlb The belief is not in reforming at a low level. The belief is that if they magnetize and you sharpen them, the metal removed sticks to the sharp edge. The first use of the blade then causes those metal shards to be raked against the edge, dulling it. – Keeta Mar 20 '17 at 17:45
  • @Keeta That is one of the theories. Also though, any long term exposure to magnets and especially scraping across and banging into magnets will tend to align iron and tend to magnetize it. That theory is that aligned iron is softer than randomized, so will tend to dull. I have never seen a knife magnetized in this manner, but will not say it is impossible, and have not seen scientific evidence that it is either possible or that it softens the metal. If makes sense in theory, but if it can actually happen is another issue. Jefromi's explanation seems more likely as cause of edge damage. – dlb Mar 20 '17 at 17:58
  • @dlb remanent magnetization is not a theory, it happens always. The strength of the effect is dependent on the material and the magnetic field it was exposed to. If or how that affects mechanical properties is another question, for which I did not find an answer. A magnetized tool is harder to sharpen (on a stone) because the small particles clinging to the edge are preventing you to get a nice polish (it is very hard to get rid of all those particles). And they gather all on the edge because the magnetic field has its highest strength there. – Arsenal Mar 20 '17 at 18:49
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There is some research going on on how to measure mechanical properties of steel using its magnetic properties. That might mean that if you change the magnetic properties of the steel (like hanging it on magnets), you could change the hardness of it - but I haven't found any article on it to support that.

A problem which might occur later on is during sharpening (on a stone, not while using a sharpening steel):

The knife will probably get magnetic over time. When you try to sharpen it, the small particles will stick to the blade, making it harder to sharpen it. So it might seem to be dull because you can't get it as sharp as before.

To get around that problem you can try to knock it several times against a wooden board (back of the blade). This will demagnetize the blade and sharpening should be easy again.

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    @Kromster shock will definitely reduce permanent magnetic properties in steel. – Martijn Mar 20 '17 at 13:09
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    @Kromster there are several ways to reduce the remanent magnetization. Usually you'd use a changing magnetic field generated by a special device to do so. Or you can heat it up beyond the Curie-point. Or you can use mechanical shock. Considering that probably no one has a tool to degauss lying around and heating it to the Curie point will reduce the hardness the only practical approach left is mechanical shock. It's not as effective as the other options, but it helps. – Arsenal Mar 20 '17 at 13:54
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    This depends on what kind of sharpening you're doing. A sharpening steel (aka honing steel) doesn't actually remove material from the blade; rather, it straightens out the edge. So it shouldn't care if the blade is magnetized or not. – David Richerby Mar 20 '17 at 15:51
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    @DavidRicherby Although the primary function of a sharpening steel isn't to remove steel from the edge, it will remove steel in cases where a depression is large enough. I have a saw sharpening business and I have special hones for very old saw blades where removal of metal is not desired. I know it still removed metal from the pile of metal dust under my saw sharpening rig even if I use a steel hone. Your hone is never made of exactly the same hardness as the item being sharpened. One will always remove something from the other. – Keeta Mar 20 '17 at 17:52
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    @Arsenal Fair enough. The average home cook probably doesn't consider any other method of sharpening, so that's an important clarification. – David Richerby Mar 20 '17 at 18:44

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