Knives Dulling with Time

[OrangeBlueOrangeBlue]

Not sure, but saw a katakana in the museum cut paper. Supposedly it hadn't been sharpened in hundred or so years.

If it was in a museum, it was likely re-polished before being put on display.

Interesting video on the subject:

 

[Spey]

I have noticed this and thought about it before. Stainless knives have Chromium in it to make the corrosion resistant. The way it works from what I understand is the Chromium in the steel reacts with the oxygen in the air and forms a Chromium oxide layer over the steel, which is what seals it and keeps it from rusting. When you sharpen a knife, you remove this off the edge and it get really sticky hair popping sharp. After it sits a while and the chromium oxide layer forms over the freshly sharpened steel, would that cause it to appear to "dull" slightly? I am not sure how thick the layer is, maybe only microns, but is it enough to change the perceived sharpness?

That chromium oxide layer over the steel is self-healing in oxygen.

chevyrulez1 post is similar to finding I came to 10 years ago when I experienced dulling, as described in OP, with VG-10 (hair whittling edge one day that disappears couple days later when edge has been left unused).

 

[000Robert]

It's amazing how well oil can hang on. Unless you are wiping with concentrated alcohol or acetone, expect a little to stick around. (This is why degreasing is an important step before acid etching, etc.) The issue is that rubbing against things does deplete that layer and often unevenly. Think about the effect of rubbing hard against a dry absorbent medium such as cardboard as it bisects around the blade. The goal of oiling in surface protection is to maintain a very light and uniform coat.

I keep a bottle of cheap, non-toxic mineral oil from the local pharmacy. To apply it, I dip a Q-tip and press the excess off the swab inside the neck of the bottle. I then dab it along the surface of a freshly cleaned blade to leave little splotches. Then I lay the side of the blade edge against a towel, desk blotter, etc. for safety and stability. I then vigorously buff it in with a cloth, rag, cotton ball, etc. to evenly distribute a very thin coat of oil. I then lightly run the Q-tip along each side of the sharpened edge. The whole process shouldn't take more than a couple of minutes unless you had to clean a really dirty blade first. (Use Zippo fluid for tape gunk.)

The key point is to leave a very thin and even coat of oil. You mostly need to create a barrier to air. Keeping the layer thin not only keeps it from being messy, it leaves the blade sticky to dust, lint, etc. Even such a thin layer will still be helpful in making some residues easier to wipe off with a cloth/rag throughout the day. The level of maintenance you need is determined by the corrosion resistance of your steel, your individual blade use, and your level of blade contact with sweat, salt, acid, etc.

Not me. I gob the Break Free on and let it sit on the blade for a while, and then wipe off the excess oil. With firearm parts I let them sit in the oil all night.

 

[The True North]

I live in a relatively arid environment, and I can store a razor sharp knife for years and the edge will be unchanged.



If you live on the coast, or somewhere with high humidity, I can see a small amount of sharpness degradation happening.

 

[herisson]

"Dulling over time"...This is a strange concept to me. My knives only dull with use. Sharp knives get stored and come out sharp as day one when needed. Yes, I live in a dry environment. So, maybe there's that. And I'm a sharpness freak : if ever a knife is not sharp as expected, I would definitely notice.