Does a patina dull the edge?

[theonew]

Awhile ago I was at a friend's house and she was making a dessert with thinly sliced fresh peaches. Since all of the blades in the house were on the dull side she was having a very hard time getting nice thin slices that didn't fall apart. So I pulled out my freshly sharpened Izula to give here a hand. After about the third peach I looked at the edge bevel which had previously been very shiny and now it had a fairly dark patina on it. It still felt sharp but just not quite as sharp as it was.

Last night after giving my Izula its weekly sharpening I decided to test this. After finishing on the ultra-fine ceramic the Izula was hair whittling sharp and would even tree top a few legs hairs (no arm hair left ). I then wrapped it in a vinegar soaked paper towel and let it sit for 20 minutes. Sure enough a nice grayish patina formed across the wide (I sharpen it with an 8 degree per side relief bevel, a 10 degree per side regular bevel and a 12 degree per side microbevel) bevel. The edge still felt extremely sharp to the touch but when I went to whittle a hair it just couldn't do it, it was close, but had lost a noticeable amount of sharpness.

So the answer to the question, does a patina dull an edge?, seems to be yes, but on the other hand it's such a negligible loss of sharpness that it isn't particularly important.

Literally three swipes per side on the ultra-fine ceramic brought it right back to hair whittling sharpness.

Here's a pic with the patina'd bevel and shiny microbevel:

 

[somber]

There's been discussion on whether oxidization/air dulls the edge before but I think it's negligible. I have never noticed that my carbon blades are more dull after they receive a patina, and in fact I would say that after a few days of rest it 'gains' a little bit of sharpness. I think this one may be in my mind, but my fingers tell me differently.

But... maybe? Sorry that's not really an answer, though.

 

[swamp]

Yes, the patina does dull your edge. But just like you noticed, not much.

 

[Broos]

Corrosion can indeed dull an edge, even more noticably on a very fine edge. I posted a link a while back to a test done by PopSci in the thirties detailing how corrosion affects a razor blade (if I recall correctly, they concluded that corrosion causes more dulling to a razor blade than cutting whiskers does), if I can find it I'll link to it...

 

[theonew]

Corrosion can indeed dull an edge, even more noticably on a very fine edge. I posted a link a while back to a test done by PopSci in the thirties detailing how corrosion affects a razor blade (if I recall correctly, they concluded that corrosion causes more dulling to a razor blade than cutting whiskers does), if I can find it I'll link to it...

I found the article in your post.

What a great read, thanks very much :thumbup: