Sharpness Chart

Status
Not open for further replies.
I should clarify that I'm not talking about a bright flashy edge, like dings and flat edges show, just a dull reflected, very thin but well defined line.
I was noting the big difference in bright flashy surface, compared to what I describe above, the other day, and thought this might be what's causing the confusion.

Oh hi. Thanks.
No I was looking for just ANY sort of reflection no matter how thin and obscure. I could see the hint of a line in the non shaving area and just nothing at all in the shave area but probably I need to use a bright flash light directly above in a darkish evening room with a more flat black back ground. The sun was fairly low in the sky due to the time of year though it was mid day.

I don't know I was just thrilled I remembered to do it while I was sitting there so used it to bump this thread to the front.

Glad I read about the cigarette paper test.
THANK YOU Wootzblade.
 
Hey wootzblade wootzblade a couple questions on the informal tests in the chart.

1. 3 finger sticky is not in the chart. I'd put it at about same level as fingernail test, a way of indicating you have a working edge. Have you heard of this test, do you see it as reliable/useful?
2. On the various paper slicing tests, like receipts and newsprint. In addition to taking shear-cut slices off the paper, do the following tests indicate any useful distinctions?
  • Whether you can push cut, versus draw cut?
  • Whether you can do it cross-grain, versus with grain?
3. On the traditional tests for cutting cleanly through toilet, tissue, or paper towel paper without tearing it. You commented here in the thread that you never took tissue paper tests seriously. I've used some of these tests in the past, always found them inconsistent at best. I had sharp knives that would 'fail' these tests sometimes, then run the same test again it 'passes.' Then I had knives that were not very sharp, that can sometimes 'pass' these type of tests. But a lot of folks in the knife using community swear by them. What was your main reason for leaving out these kinds of tests?


Additional notes:
  • The ability to "fillet printer paper" was a new test to me, had never heard of it, and has turned out to be very useful. The ability to perform that test with a blade I've sharpened correlates highly, like 100% on 10 knives I've tried it with, to the ability of that blade to shave arm hair. Which is great as a way to reduce the need to constantly shave off one's arm and leg hair to test your blades. :)
  • Planning to try the cigarette paper test at some point. I have to locate a local shop around here and figure out what kind to get. I see the Big River site has some stuff called "Rizla blue" which sounds like what you mentioned.
 
Last edited:
Hi Maximus,
Appreciate your support of the Sharpness Chart from the moment it was published here, mate.

I am aware of the 3 finger test and a few others not mentioned in the Sharpness Chart, but as the Chart already has another test in the same sharpness range, I omitted them. This Chart has never been seen as a study of all "informal tests" as you aptly named them.
But this is an interesting topic, and someone else with an edge sharpness tester may investigate them all.

Filleting paper was first demonstrated by Sal Glesser in his Spyderco Sharpmaker video.
You are right, it can completely substitute shaving forearm as requires minimum the same sharpness as for "shaving forearm against the skin with the grain of hair".

Paper slicing tests in the Chart show us variations of sharpness within the working edge range, and I didn't see much benefit to detail them as you suggest, since they are to tell us you've got a real world sharp knife.
I advise my customers to call our sharpening service when their knives start tearing print paper rather than slicing.

#3 - for the same reason as you named, "inconsistent" due to low standardization of the test media. Nowadays toilet paper is losing distinction with the facial tissue :)

The cigarette rolling paper test turned out to be pretty precise and reproducible, and informative in both cross and longitudinal push-cut. It's so common with sharpeners in some countries that I feel I have to make this test more usable by adding an international brand like Rizla.
Rizla has quite an assortment of rolling papers by thickness, let me pick one myself - it may well be the blue Rizla.
I cannot test sharpness required for push-cutting the thinnest silver Rizla simply because I don't have that sharp blades.
I will test a few and find the Rizla variety that matches the Tally Ho rolling paper.
I will update the Chart and let you guys know when ready.

Suppose my customer wants his edge to be sharper than a DE razor.
I know this by the sharpness tester score, but he will know it by the cigarette rolling paper test.
So before sending his knife back, I just have to make sure it passes the rolling paper horizontal test, i.e. cross push-cut.
 
Last edited:
I think it's worth mentioning there is a certain amount of skill involved with some of these tests. It takes a fair bit of practice to fillet paper even with a sharp blade. The bag cutting test l often use takes some technique.


Agreed. And not all newsprint or copy paper is the same.

Still, if it will do it at all is a good test and one I use often.
 
The cigarette rolling paper test turned out to be pretty precise and reproducible, and informative in both cross and longitudinal push-cut. It's so common with sharpeners in some countries that I feel I have to make this test more usable by adding an international brand like Rizla.
Rizla has quite an assortment of rolling papers by thickness, let me pick one myself - it may well be the blue Rizla.
I cannot test sharpness required for push-cutting the thinnest silver Rizla simply because I don't have that sharp blades.
I will test a few and find the Rizla variety that matches the Tally Ho rolling paper.
I will update the Chart and let you guys know when ready.

Suppose my customer wants his edge to be sharper than a DE razor.
I know this by the sharpness tester score, but he will know it by the cigarette rolling paper test.
So before sending his knife back, I just have to make sure it passes the rolling paper horizontal test, i.e. cross push-cut.

Would be interested to hear what you find. The ones I see on Big River, they say that silver are "ultra thin", green and red are "medium thin", and blue is "thin". Obviously that isn't a lot of help as it only gives an idea of them relative to each other. Also in their product description of blue, they say: "Rizla Blue Regular Rolling Papers are a lot finer and thinner than the Regular Red or Green Rizla..."
 
wootzblade wootzblade , messing around with more of the tests you posted, I tried a different combo: filleting thin receipt paper. No idea what level of sharpness this may indicate, but if you have time, would be interesting to have you test the ability to fillet thinner paper like newsprint, or receipt paper, and see if this indicates any additional/useful level of sharpness that us amateur sharpening folk :) can test at home. Here's one of my knives that I got to filleting receipt paper. A couple of slips where I cut thru, but one curl there right in the middle that did not perforate.

y4mzOsL2RwYIt_kzMxJf5auXB-YHy0MopZwS_I-mUFzvPaA6wfihGKEBD_LcIwGCocFlDyM61ewode4NdSDLsdozu8aA0xGLgOFPVFMqU-5W2QOk6ezVzAGUhmKgE4zliqatqPm7wxeIkTtA980KW1Qo4s4VFQ7sxN_SvkHvDCJf0TtM6i2x_6lr8mDoj1raP29O9hJe5VUe_S7HyYUimXqVg



ETA: I got a pack of the Rizla Blue cigarette papers, they ARE a challenging test. A good number of my sharpest folders could pass the push-cut lengthwise test, but not all. Only 3 folders could pass the push-cut horizontal test without tearing it: A ZT 0562 and Cold Steel Ultimate Hunter (both regrinds by @razor-edge-knives), and the M390 in this post that I sharpened. The tricky thing with these is, the paper is SO thin you have to really observe that you are SLICING NOT TEARING it.

FWIW: I found that thin white gift tissue paper like we get in bulk at Costco in the US is a lot cheaper than the cigarette paper, and got identical test results on my knives. For US folks this may be an economical substitute. But I guess somebody would have to test the apex width correlation.
 
Last edited:
Hi Maximus,
With the cigarette rolling paper, first we slice the paper edge to get the blade into it, then push-cut.

I've had a chance to test a sales receipt for filleting.
Filleting or rather shaving off layers of the sales docket/receipt is extremely challenging, only knives at 35 BESS i.e. near 0.07 micron edge apex start doing that.
Such a knife is sharper than a Gillette safety razor, but still not as sharp as the Feather safety razor which are the best; it roughens the cigarette rolling paper in the cross push-cut, though of course slices cleanly.
The cigarette rolling paper cross push-cut requires minimum sharpness of 30 BESS or about 0.05 – 0.06 micron edge.

On this Monday I am getting a full assortment of the Rizla rolling papers, and will update the chart then.
 
Hi Maximus,
With the cigarette rolling paper, first we slice the paper edge to get the blade into it, then push-cut.

I've had a chance to test a sales receipt for filleting.
Filleting or rather shaving off layers of the sales docket/receipt is extremely challenging, only knives at 35 BESS i.e. near 0.07 micron edge apex start doing that.
Such a knife is sharper than a Gillette safety razor, but still not as sharp as the Feather safety razor which are the best; it roughens the cigarette rolling paper in the cross push-cut, though of course slices cleanly.
The cigarette rolling paper cross push-cut requires minimum sharpness of 30 BESS or about 0.05 – 0.06 micron edge.

On this Monday I am getting a full assortment of the Rizla rolling papers, and will update the chart then.

Thanks for that, interested to hear your results.
 
Edge radius of 50 nm is unbelievable.
It is equivalent to 300 carbon atoms wide or 150 martensite grids wide.
And it is only 10 to 20 times thicker than the edge of Diatome diamond knives (2 nm radius)......
 
50 nm apex radius is a norm for straight razors - but astonishing for knives.
Freehand sharpening has always been a magic to me.
The Maximus's M390 folder edge apex radius is 35 nm. And he is still not happy.
To get my knife to fillet a receipt docket like he does, I had to use CBN wheels, jigs and computer software.
How they can achieve that sharpness on knives of that hard steel freehand without bartering away their soul, I will never comprehend.
 
Last edited:
wootzblade wootzblade , just thinking out loud with this test. Sharpened this Schrade folder (9Cr18MoV) with following progression, no micro-bevel. Usually wouldn't go thru all these steps, but experimenting with different sharpening media and seeing which ones give the most bang for the effort invested. Tested sharpness after each step, and as one might guess, noticeable improvements get smaller each step. The first point at which I could fillet a curl off the receipt was after using the SP 500-grit side. Surprisingly, the final strop on clean leather did add some value; the cross-grain draw cut was noticeably smoother, resulting cut was cleaner too. Got this idea of stropping on clean leather AFTER stropping on compound from @Todd S. site, on this page about stropping. He says in the comments section: "Additional stropping on clean leather is required, and if you prefer a very keen edge, 0.25 or 0.5 micron diamond on leather followed by clean leather works best." Tried that here; it did make some improvement.

  • Crytstolon coarse [120 grit] > SharpPebble (SP) Sic stone [320] > SP [500] > Spyderco UF ceramic [5 laps] > Strop 1 micron CBN compound/linen [10 laps] > Strop clean leather [ 10 laps]
The circled regions of the pic show with thin receipt paper this edge would: slice cross-grain chunks, push and draw cut cross-grain, and was able to shave a curl on the surface.

Like somebody said, a potential variable with paper tests is the thickness of the paper. I wonder if there's a wide variability in the thickness of common thermal receipt paper that would impact on the edge width correlations? Don't know the answer to that. I grabbed a few old receipts from different local stores, all that were printed on this common thin thermal receipt paper that seems to be the same thickness, but I can't tell as I have no way to measure that thin. I would guess there's some range in thickness--perhaps not huge but enough to be a factor.

y4mloevu2j0c9FelbkWCPUBfFUxF4BZhVnSvV6Bvpat_CyHy1JMV2QGyIq_MHeXOPdkHkaNdLdfiF807RtiivI_R5ZAck4iMrYkODI2kK4rFthGgTnd3nDYaqHGRJobOZUlvRzqt8RIcAarOncHKsF2rlU0IEyrUAo9rVIXKAyT_0vfd7UBXgRs6yz0DslPKktgCDpFTjvh_5-olUGQRTrZqA



ETA: Ran an identical knife thru the same progression, except instead of using the SP 320/500 grits, I used the Baryonyx Artic Fox 400 grit. So, one grit on the stones instead of two, all other steps the same. Gets same exact sharpness results.
 
Last edited:
With the most demanding tests, the edge oxidation effects the result. Immediately before those tests the edge should be stropped on clean smooth leather or clean linen to restore its original sharpness.
Chromium in stainless steel reacts with the oxygen in the air to form a passive complex chrome-oxide surface layer that prevents further oxygen from rusting the surface.
This film thickness originally is 3-5 nm, but can reach 20 nm on mechanically polished surface, i.e. worsen sharpness score by 5 to 20 BESS.
5 to 20 nm added to the apex radius, multiply by 2 in terms of thickness, i.e. 0.01 to 0.04 micron of added edge apex thickness.
Practically it means that the most challenging sharpness tests like the top HHT, that you can perform immediately after sharpening you can not an hour later. Oxidation can easily change your sharper than razor edge to just safety razor sharp if not duller, which is not enough for the most challenging tests.

Finally I've got a full assortment of Rizla cigarette rolling papers.

From the Rizla website: "The variation of thicknesses determines how long the paper burns for, Red papers are the thickest so burn the fastest while Silver are thinner and burn the slowest."
Smokers know that pleasure from a cigarette partly depends on how fast it burns.

I've got Rizla Silver - the thinnest, then goes Blue, Green, Orange, and Red is thickest.

Rizla_all.JPG


Tested them for cross push-cut with the same blades I used to test Tally-Ho rolling paper:
Wilkinson Sword DE safety razor - scores 30 BESS on the PT50 edge sharpness tester, has 0.05-0.06 micron edge apex width; and
a knife that scores 20-25 BESS, i.e. about 0.04 micron edge apex width.

With the Tally-Ho rolling paper, the Wilkinson Sword razor almost passes the test, but the cut is somewhat rough; the knife passes cleanly.

Silver - Wilkinson Sword razor - clean push-cut
Blue - Wilkinson Sword razor - clean push-cut
Green - Wilkinson Sword razor - clean push-cut
Orange - Wilkinson Sword razor - roughens the paper
Red - Wilkinson Sword razor - tears the paper

Silver - Knife - clean push-cut
Blue - Knife - clean push-cut
Green - Knife - clean push-cut
Orange - Knife - clean push-cut
Red - Knife - roughens the paper

The most resemblance with the Tally-Ho rolling paper has Rizla Green.

Results contradict our intuitive expectation that a thinner paper would be harder to cut.

I've updated the chart on our website
http://knifegrinders.com.au/Manuals/Sharpness_Chart.pdf
 
Last edited:
Thank you so much for testing that and open-sourcing that info in your chart, really appreciate it! I work in software and our company contributes to open source (as well as having some proprietary "secret sauce" things we make too, that's how we make $$ :)). It's really a great thing when folks can share out some useful stuff they gleaned with the larger community, and then as we are doing here, invite community discussion.

The tests on the cigarette paper are really useful for me at least, because you've done these edge width correlations, something I have no way to do. Testing with a standard paper like this is one way to solve the potential issue mentioned above, which is that common papers I test with like receipts could have some variability in thickness and composition, thus impacting informal test results.

On my other idea above about trying thin white gift tissue paper--where the goal was to be more economical--that test has not really panned out. Using it on more knives, it does not appear to get consistent results. Guessing this gets back to the same reason you gave for rejecting toilet paper, facial tissue, and towel paper tests and leaving them out of your chart: the quality of the paper itself in these kinds of low cost high volume products--things like density, composition, etc--is too variable to be reliable.

Sounds like for USA folks, the Rizla Green you tested is a good way to go, for a challenging, standard test where you've given us the apex width correlation.
 
Last edited:
I happened to talk to a rolling paper smoker yesterday, and asked him what he smokes when can't find Tally-Ho paper - guess what he answered?
- Rizla Green, mate. Others aren't quite a match.

As one Australian knife collector commented:
"I can see a lot of non smoker knife aficionados buying a lot of rolling papers in the near future..."
 
Dude, that test and the updated chart are working great. Your simple tests defining some standard testing media that are accessible to everybody (like 80 g/m2 printer paper, thermal receipt paper, and Rizla green cigarette paper) with the approximate edge width correlations, has really simplified and standardized my edge-testing. Every single knife that could at least do the with-grain cut in Rizla green, could also shave arm hair, so it's a pretty reliable correlation.

What I've simplified down to for home testing regimen, based on your updated chart. These tests are fast and easy and for me, a highly reliable indicator of the level of sharpness I want, aside from doing additional real-world tests that I sometimes do (like food prep--slice tomato, potato, or cut wedge out of apple, rope or box cut, live vine cuts--blackberry, or chopping wood with larger field knives).

Working blades (most of my kitchen, folder, and utility blades):
  • Thumbnail and 3-finger sticky tests while sharpening, at heel, midpoint, belly, and tip, to indicate a working edge or problem areas.
  • Thermal receipt paper. Shear cut a chunk off, cross-grain. Push/draw cut with grain, push/draw cut cross grain. Once I can do each of these 5 things on a piece of thin thermal receipt paper, I know the knife is at least 'sharp' or better. I find this test indicates a higher level of sharpness than newsprint, so I just dispense with any other paper slicing tests and use this entirely now as my minimum sharpness threshold.
  • Fillet a curl off printer paper without perforating it. Once I can do this, for most knives I stop. Per chart these blades probably have edge width under 0.3 micron, and for most things I do, these edges are just great.

For my best blades:
  • To the above tests, add the Rizla green test. If I can push-cut with grain, I figure in the range of 0.2 micron per chart. I've confirmed that each knife that can pass this, can also shave arm hair against grain, per chart. The cross-grain push cut, I'm finding more challenging to figure out what counts as a 'pass' of the test. A number of knives will cut it not just tear it, but you see even without magnification, some of the cuts look rougher/more ragged than others. Interested to hear your thoughts on how you decide what constitutes a pass/fail on this test.
 
Last edited:
Here's an example of what I'm talking about. Both knives above--the Buck sharpened by me, the Cold Steel reground by Razor Edge Knives--easily pass the first 3 tests in my previous post. Then I tested both for ability to push cut horizontally on a Rizla green paper. The first pic shows the setup, the Buck made the left cut, the CS made the right cut. The 2nd and 3rd pics show close-ups of the push cut results. Both knives definitely cut the paper didn't just tear it. But if I check under magnification, the left (Buck) cut up near the starting point shows just a little bit of a ragged edge, whereas the right (CS) cut is visibly cleaner near the top. Don't know if this indicates pass, fail, or just relative performance.

y4mH6WT5ibnrLr5rJnqsm60f0ojENiy_H-VJVPQjISwnPpKMVmqfuEfJ539ROs8vNB3QVm-ut5WjX7WUTR4S2YNL5thZWJu0pkWT2vxNJ7ehwrrGtwyvrvGShAL7fV9aEo0SYOqAWe_Y9vEyJMGpLSKoZBmxXp3GnDb7RQ9_B8dhrovB7BAGjianY3LHYnRksykKzqzo-iAihtNQ8SqTn5SyA

y4m_9ZQmSBGt4x72XJYM9JSCGOebEyOJI-86EUout9rHLaioeq7zUMz3vlsfkH7mXe1EG0dfGXcoagN4ZRIC69qPl4_ObSYaSdiEGZ0P1UGUR3jcVLwazjV-kTER471bJ0n1iz8Yk517cOxMq8scsKOHAepsIUbgwZca3jgioiqiz2fjT9BoGKU2YWXoPF1uFqpKXni7xHQP5aJArnL4UeX5A

y4m1iXMjbRMe1er64HSyExGW0nslwyKgIsnNc6hZsXMdhvGmJRUjH_QJytLjclNmHRgV1Lr6-MHyYF1rdheIqo8tKpShm29N9a3nS6uRcOTHYE3xrsnJ1751FNpVv1LOiag9R5cS8MiB-bDlx2fREZpCL2I0DUukNMZoE1ZdyfPHC15m48UOl5Rv2VD_GBxQvDQu1Db-BQ1bAolMxUOMzr1iQ
 
Ok , filleting print paper was easy test , notebook paper too , pass newspaper , cut small curl on my cigarette , but I can shave cigarette easy.......... :) Tomorrow I will bye some cigarete paper to try that push cut ....
Blade is 2.5mm thick M42 steel , 68 Hrc grind to zero and shaving sharp ......After that I put micro bevel 18 degrees per side /800 grit stone/ and strop on leather with some unknown paste for polishing and final little strop on clean denim ....
And I wonder what s the point in all this test ? What they proof ? How long will last two micron edge on any knife ?

5oOyuTP.jpg
 
And I wonder what s the point in all this test ? What they proof ? How long will last two micron edge on any knife ?

For me, the point is just an easy low-tech way I can use at home to indicate I've gotten a knife up to some acceptable minimum standard of sharpness, without having to go test-cut on a bunch of tomatoes, boxes, or other tests that are expensive or a hassle. In practical terms: if I'm sharpening a kitchen knife, I'd rather find out while I'm still at the stone, working on it, that it's not as sharp as I'd prefer yet. Rather than waiting until all my stones are cleaned and put away, and I'm slicing a tomato in the kitchen later, and find out it's still too dull. Or have to go cut a fresh tomato every time I sharpen the knife to find out it's sharp enough. That gets expensive. :) Most of my knives I can test up to the more basic level I posted above and don't need the cigarette paper testing or extreme level of sharpness. It's just helpful to know which of these informal tests correlates to what level of real-world sharpness I can expect.

As for the extreme sharpness and edge testing, the cigarette paper and all that: for me at least, this is not a necessity, it's more a matter of interest, and a challenge, to see how far you can go in sharpening. I'd have no expectation that edges that sharp are going to survive very long. I won't even use the cigarette paper test probably 90% of my real world knives.
 
...
For my best blades:
  • To the above tests, add the Rizla green test. If I can push-cut with grain, I figure in the range of 0.2 micron per chart. I've confirmed that each knife that can pass this, can also shave arm hair against grain, per chart. The cross-grain push cut, I'm finding more challenging to figure out what counts as a 'pass' of the test. A number of knives will cut it not just tear it, but you see even without magnification, some of the cuts look rougher/more ragged than others. Interested to hear your thoughts on how you decide what constitutes a pass/fail on this test.

Similarly to you, with my blades I've seen all variations between a perfectly clean cross push-cut, and rough.
The PT50 Edge Sharpness Tester shows that:

- roughens (still cuts, not tears) - 35 BESS or 0.07 micron edge apex width;
- almost clean cut with rough spots - 30 BESS or 0.06 micron edge;
- clean cut - 20-25 BESS or at least 0.05 micron edge and under.

(Gillette safety razors score 50 BESS and have 0.1 micron edge)

@ Natlek - there are people out there who like to push the envelope and probe the limits.

Maximus, these super sharp edges do survive on soft wood cutting boards even if made not of a super steel.
I sharpened my wife's Global Santoku to 0.1 micron, the same as a Gillette safety razor, and after 3 days of constant use it still shows under 0.2 micron edge.
This honestly surprised me, as I used to think that level of sharpness be more volatile.
 
Last edited:
Status
Not open for further replies.
Back
Top