Why+how do unused knives get dull?

[superc]

It has bothered me for decades. I have had many knives which I sharpened to shaving+ sharpness, then put them away. Years later when I take them out of the box, drawer, or off the shelf a year or five later, I find they are no longer quite as sharp as when they were put away. Oh, they'll still cut a rope or slice a box, but no longer can they be used for shaving even an arm without a touchup sharpening and honing. What is happening here? What is the mechanism that dulls a knife sitting on a shelf?

 

[bdws1975]

I believe it's due to corrosion. The edge is very thin and is prone to degradation due to oxygen corrosion.

I could be wrong though.

Brett

 

[Zeasor]

Metal-eating termites or it could be that your hair is getting tougher. Are you spending more time in the sun? Do you live near a nuclear power plant?

It's probably an oxidation process. Try oiling your blades or spraying them with a silicone-type lubricant before storing them. The termites don't like either one.

 

[superc]

Actually I have experimented with putting some oil on them. Of course 4 or 5 years later there is little trace of the oil beyond some gumminess on the blade. I can accept an oxidation corrosion of a thin edge I guess. I suppose I could sharpen a stainless blade and store it to see if that makes a difference over 4 or 5 years.

 

[mariobab]

The same question is bothering me.Often my wife asks:"So,you sharpening again.Would you please tell me where did that thing get dull?".Maybe it depends on steel.Anyway,now I checked my old 8" Solingen bowie,that is sitting in sheath for 2 last years,unknown stainless steel,and find no degradation in sharpness.Still,I stropped it,when it`s out already.

 

[nozh2002]

If knife in the pocket then I guess we can blame dust or sand. But if it sits in the shell for years - who really knows what may happen with metal on microscopic level in time? Metal structure may relax some stress, change shape a little bit etc. Like glass in hundred years actually changing shape as it is a water but very very slow. Shaving sharp edge is about few microns thick, so may be in few years it change shape in few microns and get dulled this way, at least to loose sharpness.

Thanks, Vassili.

 

[gak]

Before I store non-cooking knives I always use some car wheel polish like Eagle One Nano Polish on them. Protects the metal very well and I don't have to worry about corrosion.