Believe it or not, a magnetic rack might actually keep your knives sharp longer.
In fact, in one of those slick catalogs of expensive gadgets that no one needs, I even saw a magnetic housing for storing your razor, allegedly to keep the blade sharp between shaves. (How it would otherwise get dull between shaves was not explained.)
You may have noticed that knives kept on a magnetic rack do become magnetized. (Try picking up paper clips with them.) And according to Professor Bob O. Handley of MIT’s Materials Science and Engineering Department, a magnetized piece of steel will be somewhat stiffer than when it is not magnetized. It can probably then be sharpened to a keener edge and may stay sharp longer in use.
But don’t count on it. Knife blades are made of several different steel alloys, and some of them may not retain their magnetism very long. The stiffening effect isn’t likely to be very large in any case.
On the other hand, the careless use of a magnetic rack can indeed damage your knives if you whack or drag the cutting edges against the magnet bar when removing them or putting them back. That may be how the story got started that magnetic racks can dull the edges.
If you are worried about nicking your knife blades through hasty grabbing from a magnetic rack, you might prefer to keep them in a countertop wooden rack.
Some people think that’s really the best way. But who, besides Martha Stewart and the recipients of wedding gifts, owns a set of perfectly graduated knives, all tucked away in their custom-fitted, wooden slots? The downsides are that the slots are hard to clean and it’s not easy to tell from the protruding handles which knife you’re grabbing. With a magnetic rack on the wall, you can always select the right one for the job.
As every culinary textbook warns, a sharp knife is a safe knife; it won’t slip off the food onto a finger. There are many good electric and manual knife sharpeners on the market, so the time-honored and time-consuming method of honing them on a stone is no longer necessary.
But a word of warning: Those brute-force sharpeners containing two interleaved sets of disks through which you draw the knife blade scrape off wholesale slivers of metal that will stick to the blade if it’s magnetized. (These sharpeners are not recommended unless you like knives that get progressively skinnier.)
Metal slivers are not nice to eat, however, so after you use such a sharpener wipe the knife carefully with a wet paper towel. That’s a good idea if you keep your knives on a magnetic rack no matter what kind of sharpener you use, because abraded metal particles can be invisibly small.