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Edge Retention vs Sharpness Retention

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Gyoated

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I was watching this video where Ricky of Burrfection compared a Miyabi Birchwood vs the Black. Essentially two different steels: SG2 vs ZDP. The ZDP, obviously, had overall edged retention. But the SG2 had a longer duration of sharpness. I own a Miyabi Kaizen 1 and an Artisan. I noticed that the SG2 has a rather very nice duration of sharpness. Of course the VG10 has the legendary “meh” sharpness.
The Question is, what duration of sharpness do steels such as Aogami 1, 2, and super compare to each other or even against White steel? What of Aogami Super duration of sharpness compare to SG2/R2?
 

Jason183

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I think Edge geometry also a factor here, just found a miayabi black choil shot, they’re pretty thick behind the edge, I’m guessing miyabi SG2 is thinner behind the edge than Miyabi Black(zdp189). Maby that’s why SG2 one has better edge sharpness retention. If they both have the same edge geometry and thinness behind the edge, then zdp189 probably going to have longer sharpness retention IMO.
 

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Gyoated

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I think Edge geometry also a factor here, just found a miayabi black choil shot, they’re pretty thick behind the edge, I’m guessing miyabi SG2 is thinner behind the edge than Miyabi Black(zdp189). Maby that’s why SG2 one has better edge sharpness retention. If they both have the same edge geometry and thinness behind the edge, then zdp189 probably going to have longer sharpness retention IMO.
Without a doubt. I find the term “edge retention” very vague. There are a lot of things to factor in, such as the various grinds. But I still wonder. Perhaps between a more,or actual, skilled artisan. Perhaps Kato or Kurosaki. I know they have AS and Blue 2.
 

Gyoated

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I have read this article and it does not, at least what I remember, answer my quarry. VG10 can get sharp, but then becomes relatively sharp shortly after. It will keep it there for a long while. So it does cut for a long duration, hence edge retention. What I am curious about is the sharpness factor. And @Jason183 Knife nerd also made a wonderful article regarding the bevel angle.
 

Jason183

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Without a doubt. I find the term “edge retention” very vague. There are a lot of things to factor in, such as the various grinds. But I still wonder. Perhaps between a more,or actual, skilled artisan. Perhaps Kato or Kurosaki. I know they have AS and Blue 2.
Yes, more experienced blacksmith does make a difference, one can have white #2 in 61 HRC, another can have white #2 in 65 HRC. This is what Kato, Shige, Yoshikazu, and TF etc known for. Other than heat treatment, another thing I’m looking for in a knife steel is the grained structure(smooth vs toothie cutting feel), very fined grained like white, Swedish steel,AEB-L, gives smooth cutting feel, better for slicing. Larger carbides like AS,SG2,ZDP189( toothier cutting feel) etc, better for push cutting.
 
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Barmoley

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The above linked article answers exactly that, it also has links to other articles explaining methodology, etc. Geometry makes a huge difference and this is why geometry and edge finish are kept the same in the study. This way different steels can be compared. Comparing knives from different makers is very difficult and not very scientific as too many variables are not kept constant. Slicing edge retention is very highly correlated to wear resistance, which in turn is very highly correlated to the amount and type of carbides the steel has.
 

Benuser

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Yes, more experienced blacksmith does make a difference, one can have white #2 in 61 HRC, another can have white #2 in 65 HRC. This is what Kato, Shige, Yoshikazu, and TF etc known for. Other than heat treatment, another thing I’m looking for in a knife steel is the grained structure(smooth vs toothie cutting feel), very fined grained like white, Swedish steel, SG2 gives smooth cutting feel, better for slicing. Larger carbides like AS( toothier cutting feel) etc, better for push cutting.
SG-2 very finely grained?
 

Nemo

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I have read this article and it does not, at least what I remember, answer my quarry. VG10 can get sharp, but then becomes relatively sharp shortly after. It will keep it there for a long while. So it does cut for a long duration, hence edge retention. What I am curious about is the sharpness factor. And @Jason183 Knife nerd also made a wonderful article regarding the bevel angle.
If you reckon "edge retention" has a vague definition,

Try to define "sharp"
 

Dhoff

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Please illuminate me, how does Sharpness retention differ from edge retention? I'm likely just not knowledgeable enough. My thougts:

Two knives may differ in initial sharpness, and their edge retention may differ.

Example with arbitrary numbers:

Knife 1, initial sharpness 10

Knife 2: initial sharpness 8

Edge retention:

Knife 1, loss of 0,1% cutting power (sharpness?) per cut.

Knife 2, loss of 0,05% cutting power (sharpness?) per cut.

But I do not get how sharpness retention is not the same as edge retention....

This, of course is a simplification and would assume identical knives except for the steel and/or HT.
 
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M1k3

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Yes, more experienced blacksmith does make a difference, one can have white #2 in 61 HRC, another can have white #2 in 65 HRC. This is what Kato, Shige, Yoshikazu, and TF etc known for. Other than heat treatment, another thing I’m looking for in a knife steel is the grained structure(smooth vs toothie cutting feel), very fined grained like white, Swedish steel,AEB-L, gives smooth cutting feel, better for slicing. Larger carbides like AS,SG2,ZDP189( toothier cutting feel) etc, better for push cutting.
Finer carbides are better for push cutting, allow a higher grit. Large carbides, to a point, leave a toothier edge, better for slicing.
 
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ian

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Using "edge retention" to describe a retention of cutting ability seems wrong to me, because of the "edge" in the name. Imo, both edge retention and sharpness retention should be (synonymous) measures of the quality of the apex of the knife, not of the overall geometry. Of course, in kitchen use one should really include toothiness in whatever measure of sharpeness we use, but I guess sharpness testers mostly measure how refined and acute the apex is, since that's what affects the amount of pressure required to push a knife through a wire.

I'd use "retention of cutting ability/performance" to describe a knife that stayed usable for a long time because of good geometry.
 

Jason183

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Finer carbides are better for push cutting, allow a higher grit. Large carbides, to a point, leave a toothier edge, better for slicing.
Really? Hmmm, I found it to be the opposite in my personal experience, maby also depends on what things you’re cutting
 

Barmoley

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Really? Hmmm, I found it to be the opposite in my personal experience, maby also depends on what things you’re cutting
It is most likely due to your sharpening and not the steel. It could also be due to the particular knive's geometry. In general finer grained edges are better at push cutting, think of razor blades.
 

Jason183

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It is most likely due to your sharpening and not the steel. It could also be due to the particular knive's geometry. In general finer grained edges are better at push cutting, think of razor blades.
Maby it’s because of my sharpening, I only sharpen my knives around 800-1000 grit. I found my kintaro AS gyuto the best at push cutting the green scallion into paper thin without squeezing too much juice out of it, and when comes to slicing raw fish, all my white steels are better at it than the AS, cuts smoother without damaging the meat.
 

ModRQC

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It sure is how you sharpen then - lower grits you're putting toothier edges on everything. It does work well enough in kitchen use so as long as you like working with the results, it's all fine.
 

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I think Edge geometry also a factor here, just found a miayabi black choil shot, they’re pretty thick behind the edge, I’m guessing miyabi SG2 is thinner behind the edge than Miyabi Black(zdp189). Maby that’s why SG2 one has better edge sharpness retention. If they both have the same edge geometry and thinness behind the edge, then zdp189 probably going to have longer sharpness retention IMO.
You've got to have warning tags before posting a gross choil shot.
 

Nemo

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Using "edge retention" to describe a retention of cutting ability seems wrong to me, because of the "edge" in the name. Imo, both edge retention and sharpness retention should be (synonymous) measures of the quality of the apex of the knife, not of the overall geometry. Of course, in kitchen use one should really include toothiness in whatever measure of sharpeness we use, but I guess sharpness testers mostly measure how refined and acute the apex is, since that's what affects the amount of pressure required to push a knife through a wire.

I'd use "retention of cutting ability/performance" to describe a knife that stayed usable for a long time because of good geometry.
The science of Sharp guy argues that "keeness" should denote the degree to which the apex at the very edge is refined (i.e.: is an apex at the micron level), while "sharpness" denotes theangle thatt eh apex is sharpened at.

Just one guy's opinion, I guess but it did make sense to me.
 

ian

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The science of Sharp guy argues that "keeness" should denote the degree to which the apex at the very edge is refined (i.e.: is an apex at the micron level), while "sharpness" denotes theangle thatt eh apex is sharpened at.

Just one guy's opinion, I guess but it did make sense to me.
Yea, AFAIK they're synonyms in typical usage, but if you want to have different words for width at 3 micros behind the edge and refinement of the edge then I have no objection to using those terms like that. It seems like toothiness doesn't really factor into his definition. I'm also not really sure how he measures keenness, and it also seems to me that "sharpness testers" are then measuring a combination of sharpness and keenness.

When chiffonading toilet paper, do you guys stack sheets flat or roll them up?
Obviously, I drop a single toilet paper square from a great height and slice a perfect ribbon off of it as it falls. Then I repeat until the whole roll is transformed into a beautiful chiffonade. Then I post the video to instagram.

----

Btw, @Gyoated, if you want an answer to the OP, maybe you could indicate what the difference between duration of sharpness and edge retention is in the Ryky sense? Otherwise we don't know what you're talking about unless we watch the video.
 
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Gyoated

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hi everyone, thank you for all this input. I stated originally as “sharpness” retention and what I really mean is more along the lines of rate of deterioration and plateau of a edge’s sharpness. The only steel I can relate to is the VG10, which can get sharp, loses the very sharpness and plateaus to a modest sharpness. What I am curious of is the difference between something like Aogami Super vs 2. Does the super act like VG10. I know it wouldn’t entirely, because VG10 is stainless Speed steel consisting of Cobolt. But does Aogami Super fine toothier edge deteriorate faster than the Aogami 2 but maintain a relatively sharp edge longer? Am I making sense?
thank you all and Happy San Giving( Miami think)
 

ModRQC

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Your questions depend too much on your cutting technique, or to a larger extent what you do with the knife.

AS behaves very differently from VG-10, both in sharpening and in use. VG-10 can make you extremely happy out of the stone, but pretty "meh" pretty fast while still mostly cutting like a dream if geometry is on your favorite side. I've found the edge of AS keener than VG-10 (push cutting) and keeps a low deterioration rate under moderate abuse, but I am not impressed overall, prefer Blue #2 honestly, easier and keener, can keep an edge long enough, but mostly so easy to touch up - but then my sharpening skills/technique are counting in this assertion.

You cannot compare as easily as you'd make it to be. You need to buy the knife that tempts you in the steel that tempts you, and work with it. But the basic consensus applies pretty well I think, my sharpening skills notwithstanding.
 

ModRQC

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White #1 is easily a favorite, under the light of home use. Even softer, cheaper knives White is nice if done right, which all mine confounded are (Ittetsu, TF, Tanaka #2).

If I were to go pro, I think I'd be inclined to test some nice VG-10 against expertly treated AEB-L. Both can be impressive if geometry, again, and the edge you give, support it.

I just acquired SG2. Might be a nice contender for longevity with VG-10 while a bit steadier as an edge. But those two I'm sure cannot compete with the kind of edge I like best for push cutting, that White/Blue 2/AEB-L can give me and in home use, can endure pretty well, in order of greatness there.
 

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I'm also not really sure how he measures keenness, and it also seems to me that "sharpness testers" are then measuring a combination of sharpness and keenness.
I think he measured keenness as the width of the plateau at the very peak of the edge.
 
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ModRQC

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SKD-12: cannot personally speak of edge, but Yoshikane is sharp and keen as hell OOTB, seems to endure well. Could be a new favorite and good compromise between carbon and carbide loaded steels.

52100: cannot personally speak of edge, but might be the most promising steel I own relating to my style of cutting. That one is my next big project - I shall know soon enough.

Other steels I've tried: mention to whatever Masahiro uses in VC line - V-Toku 2? White alike for sure, darn good steel. For the rest it's on the cheaper side of things, cannot really compare.
 

SeattleB

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The science of Sharp guy argues that "keeness" should denote the degree to which the apex at the very edge is refined (i.e.: is an apex at the micron level), while "sharpness" denotes the angle that the apex is sharpened at.

Yea, AFAIK they're synonyms in typical usage, but if you want to have different words for width at 3 micros behind the edge and refinement of the edge then I have no objection to using those terms like that. It seems like toothiness doesn't really factor into his definition. I'm also not really sure how he measures keenness, and it also seems to me that "sharpness testers" are then measuring a combination of sharpness and keenness.

I think he measured keenness as the width of the plateau at the very peak of the edge.

I'm a newbie so I don't know nuthin' but I ran across the Science of Sharp articles and was fascinated. There is nothing better for learning like seeing electron photographs to know what is actually going on with sharpening. Highly recommended.

Here's what he writes about keenness and sharpness:

"A) The thinness of the edge (sharpness) as quantified by the edge width at 3 microns from the apex.

B) The edge width or fineness of the edge (keenness) as measured at the very apex of the bevel."

With correctly obtained SEM images, it is possible to measure the geometry of the edge. This can be quantified with two measurements; the edge width, or more precisely the radius of curvature of the apex and the angle of the bevel at the edge. The bevel is typically convex in the last few microns of the edge, and so measuring the angle between these two curved surface is difficult. Instead, I measure the thickness of the bevel at a distance of 3 microns from the apex. This distance is arbitrary; however, it is the relevant scale for a razor edge. For a straight, triangular bevel the angle and the width at 3 microns are related by simple trigonometry.

For convenience, I have suggested the definition of “keen” to refer to the apex width and “sharp” to refer to the final bevel angle. I suggest that this is consistent with the dictionary definitions of the two words."

The pictures are worth a thousand words: Sharp and Keen part 2
 

Gyoated

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So I took many things suggested here and applied them to the VG10. Recently I did thin it, well start(VG10 is a pain to), and strop it on a Lower grit. The result was amazing, San Giving was a success. It felt very different and keen is indeed a good word for it. I am a Push/ pull cutter myself and have used my Miyabi Kaizen 1 for more than a year now. @ModRQC I was considering AS or Aogami 2.
 

Gyoated

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Oh and Thank you all for your input!!! It was very illuminating and knowledgeable.
 

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