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Knives lose sharpness just sitting

Joined
Dec 28, 2010
Messages
29
I saw a pretty interesting thread in a shooting forum about knives.

Apparently, knives will lose sharpness over time, even when not used at all, and not exposed to rust or corrosion.

I've posted links to the entire discussion below, but here are some of the highlights:

"It doesn't really matter what method you use for sharpening, after 24hrs of the knife sitting idle it is half as sharp, that is, it loses a large portion of its sharpness by just sitting around for a short time. For a while they put this down to oxidisation of the cutting edge however recent experiments have eliminated that. Their best determination is that sharpening of any type creates stresses and distortions in the fine cutting edge that afterward relax which removes some of the gains. This happens fairly quickly, in a matter of hours. Sounds like a real bummer however there's a simple solution, that is before you use your knife simply give it a quick and light strop on leather. They've even tested how much stropping is best and concluded two strokes at 12 degrees each side are better than many strokes. Using a steel also works as long as it's not one with large and aggressive serrations. Apparently this light action resets the cutting edge to straight. (They have many micro-photos to prove it).

So, the take home is, sharp or not, strop or steel your knife briefly and lightly before every use if you want the best from it."

"The effect appears to be slightly less in high end steels. It's also slightly less if you use certain types of sharpening devices, especially those that rely on swinging diamond plates, such as TSProf or Edgepro, where you can control the application of force.

However remember that half as sharp is a relative term. Sharpness in these cases was measured in BESS units, which is a machine that measures the force taken to cut a known nylon wire, so essentially given in grams. So, what do I mean by relative? Well, if for example a knife cuts at 50 BESS it is sharper than a commercial razor blade. After 24hrs it is cutting at 100 BESS, which is still sharper than most chefs knives. So, it's not that your knife becomes a hammer overnight. The point is as Wayne says, you may have noticed this effect and now you know it's real. So a quick strop or steel before each use and all's good.

At last years Adelaide Knife Show there was a prize for the sharpest knife. It was won with a kitchen blade then went 35 BESS, which is so sharp it's unbelievable. The same knife was tested at the recent Sydney Knife Show, a year later and though unused in any way it measured 50 BESS, which is still twice as sharp as the best chefs knives, but half as sharp, if you see what I mean. A quick strop on untreated leather and it was back in the 30's. It's good that there is such a simple solution to this."



https://www.ballisticstudies.com/Resources/Discussion+Forums/x_forum/22/thread/17793.html

https://www.ballisticstudies.com/Resources/Discussion+Forums/x_forum/22/thread/17109.html
 
Joined
Dec 16, 2012
Messages
4,437
It's corrosion from atmospheric humidity. Unless it's on a steel like M390, Elmax, LC200N, or H1 steels will corrode the tiniest bit on the microscopic level. I've seen this mostly on my carbon steel knives, surprisingly not on Maxamet though. I have seen it on HAP-40, Super Blue, M4, and K390, 1095, and L6. D2 has it happen too, but not often, and I have seen it once with ZDP-189.
 
Joined
Dec 23, 2005
Messages
1,736
S110V does very well on this aspect.
A PM2 in this steel with a full mirror edge (up to 1.0 micron diamond compound on a Paper Wheel) could whittle a chest hair from root-to-tip right after sharpening, and after little over a year being pretty in a display case (never used) the apex could still do the same thing.
There was a difference however; right after sharpening the knife could whittle the hair a little further away from the point of holding.
But the fact that it was of course a different chest hair could also have played a role, :)
 
Joined
Jan 8, 2013
Messages
1,353
In the OP, who is this “they” who does the testing? Maybe we could just read the tests.
 
Joined
Aug 10, 2013
Messages
8,037
....I've posted links to the entire discussion below, but here are some of the highlights:

"It doesn't really matter what method you use for sharpening, after 24hrs of the knife sitting idle it is half as sharp, that is, it loses a large portion of its sharpness by just sitting around for a short time. ...
Do people really believe this BS?
 
Joined
Jan 31, 2018
Messages
2,652
we should summon Larrin Larrin to weigh in ... I don't dismiss it off hand, but I really do find it hard to believe a minor layer of surface oxidation could impact the test so much
 
Joined
Nov 27, 2018
Messages
397
I heard some guys "experimenting" with a straight razor and a magnet. Seeing if the magnet will straighten the edge instead of stropping. Pointing the razor edge north etc. It's all voodoo bs. And some guys buy it cuz "someone said so". Lol.
 

not2sharp

Platinum Member
Joined
Jun 29, 1999
Messages
19,251
Lost me at “after 24hrs of the knife sitting idle it is half as sharp”.

Negative

Half as sharp as what? It probably loses much more sharpness from slicing through a single sheet of paper. This is not going to impact user's real world performance.

n2s
 

Lance Leon

Gold Member
Joined
May 3, 2017
Messages
898
On a scientific level, yes. The steel will oxidize and also the edge will try to 'bend back' to it's original position. But how much this matters at a practical level, I couldn't tell you.
 

madcap_magician

Platinum Member
Joined
Feb 27, 2005
Messages
5,397
If this is true, it doesn't seem to have a practical effect at any level even the knife OCD people that most of us are would notice.
 
Joined
Dec 26, 2018
Messages
77
The 'half as sharp after 24hr' bit is likely only true with a CRAZY sharp knife, something way sharper than a razor, like discussed in their testing. That thin of an edge, any change (either from the steel 'relaxing' or oxidizing) could mean it took twice as much force to cut something. BUT, at that level, when the force to cut right after sharpening is X, and X is such a small number, even 2X is still really, really, really small - aka, it's still really, really, sharp. A person using the blade likely isn't sensitive enough to feel the difference between X and 2X.

In a knife that actually gets used (like a pocket knife or kitchen knife) that isn't many times sharper than a razor blade (aka the edge isn't insanely thin), I bet instead of X -> 2X, it's probably more like X -> 1.0001X
 

Larrin

Knifemaker / Craftsman / Service Provider
Joined
Jan 17, 2004
Messages
4,488
They are talking about this video:

When looking at razors they are extremely sharp to begin with. Just by breathing on them funny (slight exaggeration) you could end up requiring twice the force on that sharpness tester.
 
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