is it just me or?

T

TheGoldenWalrus

Joined
Jul 16, 2011
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433
Is it just me or does fruit significantly dull your knives aswell?

it seems no matter how sharp my knife starts, by the time i finish eating an apple or an orange it's significantly duller, ofcourse it is still quite usable but just doesnt seem like an apple could dull a knife that much that fast.

am i doing something wrong or that just how it is? do you have this "problem"?


Thanks,
Scott
 
I do not have that problem Scott but I dont eat a lot of fruit. Never noticed any dulling after an apple or peach. What brand knife and steel are you using? Whats your sharpening process? Do you know what degree your edge is sharpened to?
 
I have a well seasoned knife, 100+ years old that keeps a razor sharp edge forever as long as I don't cut on glass, (and all that really takes is steel to realign the edge) and I have a 10 year old knife from a certain PA manufacturer that goes dull just sittin' in the drawer.
 
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well just now i was useing my peanut in CV, my sharpening process is the "average" sharpening process, run it on one side until it reaches a burr and then the other, and then alternateing until it evens out, and then stropping. and i'd assume the angle is probably around 30 inclusive. or atleast i'd assume it is.

Edit: woops probably more like 35 or 40. angles confuse me sometimes :P

Scott
 
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Well maybe the heat treat of your particular blade is off a little? Maybe try taking the edge down a bit? I like my edges pretty thin and as long as I dont twist cut I usually dont find the edge getting any more damage then it would regardless of angle. Like hitting a metal staple when cutting thick cardboard, doesnt matter what angle your blade is at, it will probably get a ding anyway.
 
This may sound strange to some but sometimes (and this has happened very rarely) I have gotten to where a knife maintains it's edge better than from the factory with the factory edge. Not sure if it was a "heat treat" thing near the edge or not?

OK did that make sense to anyone reading this :confused::)

Paul
 
Im glad you posted this. Therefore I am going to say what i have to say and i ran tests. Eating any food that results in patina (with a carbon steel knife) will make the knife duller. The test i ran including just spreading the "juices" or "acids" on the blade instead of actually cutting the food (i figured this would leave no argument, because the actual cutting of food could dull the knife). I found that the juices alone made the knife duller. I tried to find why, and i came up with the reason that your perfect stropped edge gets a bit duller because it develops a bit of rust (ask Frank, even patina is "black rust"), therefore dulling the knife.

I thought i was crazy at first, but its just fact.
 
well i really dont think that its a heat treat issue, as i have had a knife with a heat treat issue and i would certainly recognize such a thing.
and i was thinking along the same lines as Shrapne1 while i was speculating on what might cause this. im now thinking on getting some higher grit stones. as that might polish the steel leaving smaller and fewer pores. meaning possibly more rust resistance? or maybe i should get a stainless knife to use for food.... or both :D

Thanks,
Scott
 
Acids will corrode carbon steel more or less instantaneously (at a microscopic level), which removes steel from the edge as the oxidized (rusted) iron sloughs off. The blue/black staining of the fruit, from the blade, is visual proof of this material coming off. Every time a 'new' patina is applied to a blade (via fruit acids or whatever), the dark residue that comes off the blade is iron being removed from it (in the form of iron oxide). It happens that easily. The extra chromium in a stainless blade prevents that (or at least, slows it down greatly), so there's nowhere near as much steel lost at the fine edge. So, on a non-stainless blade at least (like CV), I could see that the edge might become dull more quickly, when used to cut fruits or other acidic materials.


David
 
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It sounds reasonable to me, that a non-stainless blade may (on a microscopic level) "lose" its razor edge from exposure to corrosive or acidic liquids.
 
TheGoldenWalrus said:
well i really dont think that its a heat treat issue, as i have had a knife with a heat treat issue and i would certainly recognize such a thing.
and i was thinking along the same lines as Shrapne1 while i was speculating on what might cause this. im now thinking on getting some higher grit stones. as that might polish the steel leaving smaller and fewer pores. meaning possibly more rust resistance? or maybe i should get a stainless knife to use for food.... or both :D

Thanks,
Scott
Click to expand...

Very interesting observations. I shall pay attention next time I eat a piece of fruit. I like your approach with the polished edge, may be just the ticket to slow down that edge dulling while still keeping carbon in your pocket.

Learn something new every day and maybe I am just not getting my edges sharp enough to tell a difference. Or maybe I dont eat enough fruit? :D At any rate I will surely pay close attention next time I cut into some.
 
Scott, I agree with the acids in fruits etc... I did a forced patina once and my blade had a razor edge before but not afterwards (apple vinegar). The suggestion I was trying to make (feebly mind you) was once I had a knife with a factory edge that would roll if you looked at it funny.

Others had mentioned that a bad heat treat was possible along the edge but after a few sharpening's one could get past that to where the actual heat treat was where it was suppose to be.

There, after all that I agree with the corrosive being the culprit :D

Paul
 
paulhilborn said:
This may sound strange to some but sometimes (and this has happened very rarely) I have gotten to where a knife maintains it's edge better than from the factory with the factory edge. Not sure if it was a "heat treat" thing near the edge or not?
Click to expand...

Not strange at all. You have to remember that production knives are quickly sharpened on machines. Most of the time the edge that results is rough and has a burr. This less-than-perfect edge will not last as long as one that is sharpened properly.

Sharpening on machines also requires a light touch. If you are too heavy handed, or in a rush, you can easily burn the temper on the very edge of the knife. Until you sharpen this area away your knife won't hold an edge very long. I've seen this on a few knives where the tip was discolored. I noticed that I had to resharpen the tip more frequently than the rest of the blade, at least at the beginning. After a while this phenomenon went away, I can only assume that by that time I had gotten to the "good" steel.

Obsessed with Edges said:
Acids will corrode carbon steel more or less instantaneously (at a microscopic level), which removes steel from the edge as the oxidized (rusted) iron sloughs off. The blue/black staining of the fruit, from the blade, is visual proof of this material coming off. Every time a 'new' patina is applied to a blade (via fruit acids or whatever), the dark residue that comes off the blade is iron being removed from it (in the form of iron oxide). It happens that easily. The extra chromium in a stainless blade prevents that (or at least, slows it down greatly), so there's nowhere near as much steel lost at the fine edge. So, on a non-stainless blade at least (like CV), I could see that the edge might become dull more quickly, when used to cut fruits or other acidic materials.
Click to expand...

I think it's a combination of things. It's the microscopic corrosion on the edge as you said, but it's also the fact that the patina that results also increases drag. A polished surface (in this case the edge) glides through material more easily than one that is rough.

- Christian
 
well i figure on just getting a stainless knife specifically for food, and keep my carbon for everything else.
maybe a nice tiny toothpick. or a stainless opinel.... or some other single blade stainless traditional :D
my wallet is going to hate me.....

Scott
 
kamagong said:
Sharpening on machines also requires a light touch. If you are too heavy handed, or in a rush, you can easily burn the temper on the very edge of the knife. Until you sharpen this area away your knife won't hold an edge very long.

- Christian
Click to expand...

Agree with this 100%. Even when a discoloration is not visible, the edge and the metal behind the edge can be either too soft or too brittle, depending on how much heat was generated and how quickly it dissipated during sharpening. I've seen it more on chisels than with knives, but generally it has not spread too far into the blade, and moving the edge past that that zone will resolve the problem. Of course, taking a chisel back 1/16 or 1/8" is more acceptable to me than taking a knife blade back that much!
 
Interesting, my knife's main occupation is cutting apples, and I always wondered why the knife always needed a strop at the end of the day for cutting through such soft material - its not as if I was cutting through cardboard or wood or something that would obviously hurt the edge.
 
RonnieC said:
Agree with this 100%. Even when a discoloration is not visible, the edge and the metal behind the edge can be either too soft or too brittle, depending on how much heat was generated and how quickly it dissipated during sharpening. I've seen it more on chisels than with knives, but generally it has not spread too far into the blade, and moving the edge past that that zone will resolve the problem. Of course, taking a chisel back 1/16 or 1/8" is more acceptable to me than taking a knife blade back that much!
Click to expand...

Interesting. It may explain WHY my CASE TJ in cv is useless at holding an edge or even obtaining one!

I agree with fatcorgi's experience. I strop my fruit cutting knives on cardboard after use, I do suspect acids&sugars, pears are the worst:D:eek:
 
well it seems as though i may have overracted by saying significant dulling.... cut up an apple and an orange today, and it still cuts find, with just a little rougher feeling, otherwise cutting the same. so its not significant, just noticable. still kindof annoying as i sometimes spend up to an hour getting a GOOD edge on my knives, just to see it go down to a fairly good edge from cutting an apple. but i guess its nothing to really fret over, but still think i might get a stainless knife. might switch to stainless if i can find one i like. i can sacrifice patina for a sharper edge.
so while im here, anyone know of a good stainless compairable to a carbon in performance? (besides opinels inox steel, as i already know of that, but really want a slip joint, just love that click :D)

Thanks,
Scott
 
Learn to use a strop. A few passes will restore a carbon steel blade's cutting efficiency, at least for the uses you have in mind.

- Christian
 
i do strop but i probably need to get my technique down. and probably a better strop, as im just useing the back of my belt.

Scott
 
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