Unused Edge: How long to degrade?

I too have had the distinct impression that some knives lose their sharpness over time, just by sitting there.

I'm left wondering if it is just me, or did they really lose their sharpness...
 
I have a custom from my uncle Glen Hornby ( a deceased maker out of California). It has never cut anything. Never a piece of paper, or anything.

It has never been stored in the sheath.

It is stored in a soft terricloth roll, with nothing in there.

It won't shave anymore. In fact, it is pretty dull now. It was laser sharp when I received it.

It is stainless.

But when you think of it, when I get it out to look at (only once every couple of years), I have always tested the edge with my thumb.

A blade that you carry in your pocket, even if you never take it out, or feel the edge, or use it, is still in a humid pocket.

Most people live in air that will oxidize exposed high carbon steel if left out. If you live in higher humidity, even worse.

You pocket, while I am sure it is a great place, otherwise, will be more humid than the air around you.

I have no explanation for knives that stay sharp when they have been sitting in a swamp, exposed to the elements for 200 years and 3 days, and were covered in blood when dropped in said swamp.

I would be willing to bet, that the razor that has sat exposed to the elements for 20 years, with no protective layer at all, really, if you had it analyzed, has a micro thin layer of dried up protection on it.

Knives, that have spent their entire lives in a leather sheath, handed down from Uncle Jimmy, and are still laser sharp, probably have been sharpened at some point in that existence. And, if Uncle jimmy knows anything about knives, he probably put it away with some protection on the blade.

Some steels maintain an edge much much longer than others as well.

Many factors contribute to this.

Higher hardness, Carbon content, Carbides, etc etc.

A polished convex edge will probably maintain sharpness when neglected than a rough toothy edge of the same steel. Less surface area.


I don't pretend to have all the answers, but there are explanations for everything.


My uncle, whom I respect very much had a conversation with me about edge "evaporation" when I was a youngster. I don't remember the exact conversation, but remember that exact phrase, and I thought it was odd.

Steel may appear solid, and unchangeable, but you can take two pieces of steel, give and identical heat treat and temper, but take one on a deep cycle cryo treatment and get better properties like Edge retention etc. Why, would making the solid, cooled steel very very cold have any effect, if the steel, was in fact, in a state that it could be changed by a cooling down below room temperature.

Glass is a liquid, if left in one position, after a an extended period of time, the base is thicker, and the top is thinner.

Glass is much harder than steel knife steel, but there are molecular structures that are responsible for this.

I am no scientist, or chemist. I can't explain how a black hole so dense it won't allow light to escape exists (well, ok, I can explain that one). I also can't explain why some black holes pulse plasma jets out either pole, when light can't get out.

Just because I can't explain it, does not mean it does not happen.
 
Edge corrosion is real and will happen to almost any knife edge. Its not gizmo its science......
 
Edge corrosion definitely happens. Not to all my knives, but I notice it on a few, especially carbon steel ones. I have a carbon Mora that I leave in my trunk, and at least 3 times I sharpened it and a couple months later it would barely shave. This time I treated it liberally with a corrosion inhibitor/protective coating and it stays super sharp.
 
That's why Spyderco is using H-1 in the JumpMaster. Those guys needed a knife that wouldn't lose its edge to corrosion while sitting around, because when they do need it, lives are at stake.
 
Depends on the steel, humidity, and if it is stored in the leather sheath.

Some knives do dull after sitting in the sheath for a year. It may be oxidation, I dunno.
 
I'm curious to see if an H-1 knife will get dull over time.. if so then its not just corrosion dulling the knife as H-1 cannot rust.
 
When people say knives stay sharp when unused over a long time, I need to know his definition of "sharp". I got knives that lose their hair whittling sharpness after sitting in the drawer for a while, but they're still sharp enough to shave hair off my forearm all day. If your test of sharpness goes up only to the level of forearm shaving, then it appears that those knives never lose their sharpness.

I believe it's micro corrosion, because even stainless steel corrodes.
 
Anything above absolute zero has heat, or energy, and the atoms vibrate. As the energy, or heat, goes up the atoms vibrate more until at some point they break free from each other and move around freely (turn to liquid). When you heat it even more they move around even easier until atoms or molecules separate from each other and float away (turn to vapor). This can be seen easiest with water as it turns from ice, to liquid, to steam. Obviously this is a simplified explanation but is the gist of how things work.

Things in our physical world also like to move from a state of higher energy to lower energy. A high concentration to a low concentration. Things like to even out basically. Rain drops aren't square or jagged, they are round. The high spots even out until they get as stable as they can which is basically a sphere.

When you have a blade that is sharpened down to a few atoms/molecules thick it is at a higher state of energy. Since the atoms are moving they are also held in place by fewer atoms around it. Eventually the atoms that are at the thinnest part of the blade, the very edge, will flop over so that they are at a lesser energy and supported by more material. Eventually they will get to a point that they are stable at and won't move around much after that, a sort of equilibrium. This is again over simplified but basically how things work.

So it should be possible for a sharp edge to lose some of it's sharpness. How much, and how long it takes I'm not sure, but it should happen according to various physics and thermodynamic theories. More than likely oxidation will have a bigger and quicker effect, but it's not the only way a knife can dull on it's own over time.
 
So, let me get this straight . . . blades dull over time because gremlins invade our pockets where — because they are being influenced by aliens — they vibrate at a high rate of speed, causing rapid heating and cooling of the steel, which causes molecules to mis-align, which causes dullness? Okay, I think I got all that, but where do the gremlins come from, and why do they invade our pockets?

Being serious for a moment, I’ve had edges degrade over time, too, but have no explanation. I just re-strop them, and let it go at that.
 
tyr_shadowblade said:
Depends on the steel, humidity, and if it is stored in the leather sheath.

Some knives do dull after sitting in the sheath for a year. It may be oxidation, I dunno.
Click to expand...

We have a winner!

The environment plays a large part in how a knife edge will wear. The harsher the environment, the more often you need to examine your tools.

The OP lives in the Philippines, if you've never been there, it is hot & wet, plus if he carries it, body sweat & the salts can also get onto the blade edge.

As for leaving a knife in a sheath long term, don't do it, especially if leather or fabric as they will absorb moisture and hold it right next to your knife. For storing knives long term, take them out of the sheaths and give it a coat of grease, or wrap in corrosion-inhibiting paper.
 
When you have a blade that is sharpened down to a few atoms/molecules thick it is at a higher state of energy.
Click to expand...

I (respectfully) disagree.
In theory you can get obsidian sharp unto molecular level because that's the way these molecules will break. On the other hand even the keenest razor edge that you can put on a steel blade using normal sharpening gear will still be several millions of atoms wide so this phenomenon won't have an effect at this scale.
 
Dagon said:
I (respectfully) disagree.
In theory you can get obsidian sharp unto molecular level because that's the way these molecules will break. On the other hand even the keenest razor edge that you can put on a steel blade using normal sharpening gear will still be several millions of atoms wide so this phenomenon won't have an effect at this scale.
Click to expand...


You are probably right that most edges are quite a bit thicker than that. I don't think it is anywhere near millions of atoms wide but I haven't looked anything up either. Gold leaf can be beaten out so that it is only a few atoms thick. While an edge will be quite a bit thicker than that I don't think it will be a million times thicker. What I stated was theoretical but I still think atoms can move around enough that the edge can dull some. Atoms of alloying elements have been found to move around and distribute themselves in steel to a certain extent. If they can move around that much then I think it is possible to dull some. Again, this is somewhat theoretical and I could be wrong but others who mentioned entropy also think it is a possibility.
 
FlaMtnBkr said:
You are probably right that most edges are quite a bit thicker than that. I don't think it is anywhere near millions of atoms wide but I haven't looked anything up either. Gold leaf can be beaten out so that it is only a few atoms thick. While an edge will be quite a bit thicker than that I don't think it will be a million times thicker. What I stated was theoretical but I still think atoms can move around enough that the edge can dull some. Atoms of alloying elements have been found to move around and distribute themselves in steel to a certain extent. If they can move around that much then I think it is possible to dull some. Again, this is somewhat theoretical and I could be wrong but others who mentioned entropy also think it is a possibility.
Click to expand...

Well, I did a quick check.

An extract:
"The size of an atom is difficult to describe because atoms have no definite outer boundary. To overcome this problem, the size of an atom is estimated by describing its radius. In metals, this is done by measuring the distance between two nuclei in the solid state and dividing this distance by 2. For nonmetallic elements, that exist in pure form as molecules, measurements can be made of the distance between nuclei for two atoms covalently bonded together. The diameter of an atom ranges from 1 × 10-10 m to 5 × 10-10 M."

Imagine we sharpen the edge to 0.01 mm, this is 10 e-5 m
In that case with a diameter average of 1x 10e-10 m, then there are 10e5= 100.000 in the width of the edge. Indeed an order of magnitude less than my "millions" guesstimate, but in my opinion still largely enough so that low level atomic behaviour won't be the reason for any dulling.

I still expect microcosmic corrosion to be the deciding factor, if it happens.
 
You must log in or register to reply here.
Back
Top