Spyderco Forums

I sharpen a stainless steel Spyderco until it is effortlessly push-cutting thin curved ribbons of paper. Since I'm sharpening several knives in a batch, I don't use this knife immediately, I put it in the drawer. Two months later I want to carry it...but find it no longer push-cuts cleanly, as it did months ago.

I live in a dry desert climate so moisture isn't an issue. The knife has been folded and the edge has not been knocking against anything.

Is this my imagination? Or is a loss of sharpness actually happening over time, in the absence of any other dulling mechanism?

Completely theoretical.

Perhaps it is the force of gravity over time, causing the edge to curl downward on a micro level.



It's probably just edge corrosion on that same micro level.

I recall a long thread about this on BladeForums years ago. The anecdotal reports all involved stainless steel knife edges somehow self-healing from a very keen edge to one more rounded, just sitting in a drawer. I had it happen on my West German Puma Deer Hunter, but not on my SAK’s.

These phenomena are very hard to verify objectively.

Well, just chemistry. There is going to be some loss of atoms to the atmosphere and to things around the steel. Over long periods (years) it could theoretically lose sharpness.

There is residual burr on the edge until proven otherwise.

Have to rule out the simple stuff first.

"Is the TV plugged in?"

I remember reading an article in a knife magazine way back in the 1970s that discussed edge loss from just sitting around happening to carbon steel knives due to oxidation, or whatever.

Jim

Carbon steels will lose their edge to corrosion over time, I wonder if even stainless isn't susceptible to this on some level.

What if next time you sharpen, you then seal the knife in a baggy or something with a desiccant pack? For science?

I asked Mr. Stamp about this years ago and his theory was that during sharpening there was some elastic deformation and that with time the edge would “relax” a little and lose a little bite.

I don’t know if that is true but it has always stuck in my head.

can't say i've seen it. i've bought 10-20 year old NIB knives that still effortlessly shaved. i have carbon moras that haven't been used in a decade that'll cleanly cut receipt paper.

I've opened boxes of kitchen knives made in the 60s never used that were still razor sharp.

I’ve experienced this also and have been left to conclude (somewhat inconclusively) the following:
One could argue that one’s sharpening skills continue to improve over time. What was once considered to be a “very sharp” edge may now only be considered a “medium-sharp” edge. I’ve asked myself, “Did the once “very sharp” edge gradually degrade over time on its own, or did my sharpening technique just improve?” The only thing that disproves this theory are the knives that have never been used or re-sharpened. For example, I have a plain edge ZDP-189 blade that remains wickedly sharp after around 8 years of non-use. I also have a plain edge H1 blade that has never been used over the course of 8 years, but it no longer has the “hair-popping edge” like it used to when it was new. As already mentioned, it would be interesting to see if sealing the knife in a plastic bag with a desiccant pack would make any difference in edge retention over the course of several years.

With one of the USB microscopes you take a picture daily of freshly sharpened knife to see if there is something going on with the edge.

Evil D wrote: ↑

Wed Sep 08, 2021 3:03 am

Carbon steels will lose their edge to corrosion over time, I wonder if even stainless isn't susceptible to this on some level.

This would be my guess, maybe the formation of a thin passivation layer over time. Or perhaps mood congruent memory effect... Was it really quite as sharp as we remember it? Maybe there was a slight hitch when initially push cutting and we subconsciously decided it was plenty sharp and went on to the next project. When recalling later, all we remember is push cutting and thinking "plenty sharp"

I didn't remember anything about low temperature creep in steels that could lead to "relaxation' or edge "healing" over time from my materials classes... Some polymers sure, but steel?

Even diamonds loose a bit over time. That is learned in basic science (of course it takes a real long time to be noticeable), so it would not be too far fetched to believe that a knife edge would lose its sharpness over time due to electron or atom loss, corrosion, and etc.

Buddafucco wrote: ↑

Wed Sep 08, 2021 4:50 am

What if next time you sharpen, you then seal the knife in a baggy or something with a desiccant pack? For science?

You'd probably need to go further than that, I have knives that are more or less sealed in their factory bags inside boxes that have lost edge bite. Maybe you could coat the edge in Vaseline or something to seal out the air completely?

Deadboxhero wrote: ↑

Tue Sep 07, 2021 11:20 pm

There is residual burr on the edge until proven otherwise.

Have to rule out the simple stuff first.

"Is the TV plugged in?"

Agreed...


Eggzaklee...

vivi wrote: can't say i've seen it. i have carbon moras that haven't been used in a decade that'll cleanly cut receipt paper.

Same, and with various stainless knives too

JRinFL wrote: With one of the USB microscopes you take a picture daily of freshly sharpened knife to see if there is something going on with the edge.

^^^ Yep, this too ^^^

u.w.

Lmao, yup

u.w. wrote: ↑

Wed Sep 08, 2021 8:19 am

Deadboxhero wrote: ↑

Tue Sep 07, 2021 11:20 pm

There is residual burr on the edge until proven otherwise.

Have to rule out the simple stuff first.

"Is the TV plugged in?"

Agreed...


Eggzaklee...

vivi wrote: can't say i've seen it. i have carbon moras that haven't been used in a decade that'll cleanly cut receipt paper.

Same, and with various stainless knives too

JRinFL wrote: With one of the USB microscopes you take a picture daily of freshly sharpened knife to see if there is something going on with the edge.

^^^ Yep, this too ^^^

u.w.

I guess you could go all out and do a BESS sharpness test at the same time daily while recording temperature & humidity. That would help rule out human variables.

I've noticed this too. I've never really mentioned it because I figured people would think I'm crazy lol