10-21-2017, 03:29 AM
(This post was last modified: 10-21-2017, 06:30 PM by KnifeGrinders.)
This is an excerpt from my article in the Australian Knife Magazine.
Australian Knife Magazine is a printed magazine, and I seriously doubt anyone in the US will ever have a copy unless I send them, but I won't.
I therefore thought making this data available to the BESS forumers.
Knife community uses a set of fanciful terms to describe sharpness.
These terms, although not academically endorsed, are full of meaning as they come from real life, flesh and blood cut off our fingers.
They may sound vague and not clearly defined, but are discriminating enough for us. We readily distinguish a work sharp edge from shaving sharp, and will never confuse a scary sharp knife with crazy sharp.
Sharpness reflects the very edge itself, not overall performance of a knife, which is subject to cutting tests and not discussed here.
On the one hand, we have our informal classification of sharpness, like working edge - sharp edge - fine edge etc (I am listing the full terminology in a paragraph);
on the other hand, we have a set of tests telling us how sharp the knife is, like thumb pad test - fingernail test - shaving test etc, and again I will give a complete list of these tests further on as they are so inventive that can capture imagination.
Armed with a BESS PT50 edge sharpness tester and a few hundred knives from our rental pool and my collection, started I my study, full of curiosity and apprehension.
DEGREE OF SHARPNESS
Dull - an edge over 500 BESS.
Butter knife is a classic example of ultimate dullness.
Plastic knife from the last Sydney Knife Show cafe scored 1750 BESS;
Plastic knives they give us at airlines are 2000+ BESS.
An edge over 500 on BESS scale requires sharpening.
Sharpness in the range of 200-400 BESS.
Working edge, real world sharp is within 300-450 BESS.
Sharp we call an edge at 250-300 BESS. Quality cutlery out of the box comes that sharp.
Very sharp - most people consider it an edge between 130-200 BESS.
Fine knife edge takes us to the quarter of a micron level, 100-150 on BESS scale.
Shaving sharp - edge starts scraping shaving at 160 BESS - and we will discuss all the gradations in the Sharpness Tests section later.
Nuts sharp referred by knife lovers is an edge at 0.2-0.3 micron, 100-150 BESS.
Scary sharp edge is at 0.2 micron or scores 100 BESS.
Further to the submicron level, under 100 BESS, we start talking of keenness rather than sharpness.
Not many people have the skill, knowledge, or equipment to reproduce this edge.
Crazy sharp starts just under 0.2 micron, from around 90 BESS.
Razor sharp – for example, a double-edge Schick razor from Woolworths is 30 BESS.
Knife edges in this range have insane-this-should-be-illegal levels of sharp.
Wickedly sharp is a term reserved for edges under 0.3 micron, which is less than thickness of a human hair cuticle.
And finally, esoteric sharpness.
A silk scarf dropped on the edge cuts in half by itself.
Sharp enough to shave a gnat’s ballbag.
SHARPNESS TESTS or HOW TO KNOW HOW SHARP IS YOUR KNIFE
Now that we have the edge sharpness tester from Mike, these tests are no more than historical for me, but I will always be feeling sentimental about them as they've been the only means guiding my sharpening for decades.
Values I give further is the earliest attained sharpness (from the dullness end of the range) when the test can be performed cleanly.
Thumb Pad Test - feeling the edge crosswise with the ball of your moistened thumb. Draw your thumb across, not along, the edge to feel how it grips into your thumb print. If the edge tickles your thumb the knife is not dead dull. This is a widespread belief; our tests, however, show it is false.
Just today an electrician brought me his knife to sharpen, which scored 795 BESS, yet it still tickled my thumb.
Too subjective to be a useful test.
Fingernail Test - resting the edge with its own weight on your nail check if it catches. When it sticks, it is sharp. If the edge glides over your nail, it is dull.
I’ve tested a dozen of knives from 800 BESS edge down to 200 with a 50 BESS step to determine the catching point, and the fingernail test becomes positive at 350 BESS.
This one is a truly useful test as it tells you have a working edge.
![[Image: Fingernail_test.JPG]](http://knifegrinders.com.au/photos/Fingernail_test.JPG)
Whittles soft wood (e.g. pine) – becomes positive at 150 BESS.
This is shaving range, which has a number of well-defined gradations that we will discuss at great length after the paper tests.
Paper Tests
Roughens & tears paper – a knife starts tearing paper at 600 BESS, not duller.
Obviously, such a knife requires sharpening.
Slices 80gsm printer paper – a knife can do it at 450 BESS, which is the upper limit of the working edge.
Not a very clean cut initially, but already effortless; the sharper the edge the cleaner the cut.
Slices newsprint – this is somewhat more demanding, and indicates an edge within a good working range, at minimum 400 BESS.
Slices a sales docket/receipt – as these dockets are very thin, the test is even more demanding for sharpness, and becomes positive at 300 BESS.
When positive, this test takes the edge from just working to sharp.
Filleting printer paper, i.e. shaving off layers of 80gsm paper not cutting through, first demonstrated by Sal Glesser in his Spyderco Sharpmaker video.
I’ve tested a good dozen of knives slightly differing in sharpness to precisely determine how sharp must be an edge to be able to shave paper – at 130 BESS or a quarter of a micron.
Pretty sensitive and precise test, indicating a very sharp fine edge.
Only knife that sharp will cut a circle in light printer paper.
![[Image: Filleting_paper.JPG]](http://knifegrinders.com.au/photos/Filleting_paper.JPG)
Toilet paper test - push through then slice down a single ply toilet paper. Possible at 50 BESS.
The main challenge of this test I found was to harvest that single ply. Unfortunately, nowadays this test is losing its standardization power since the test media is losing the line of distinction with the facial tissue.
Shaving Tests
Scraping shaving – a toothy edge is capable of catching hairs on the skin, but instead of cutting them it “rips” them out of your skin: 160 BESS or about 0.3 micron.
Shave against the skin - won't shave arm hair above skin, but shaves touching the skin without trouble.
This test has two gradations:
- with the grain of hair – 140 BESS; and
- against the grain, which requires way better sharpness in the vicinity of 0.2 micron, 95-100 BESS.
This is the level of sharpness the knife community refer to as “nuts” and “scary sharp”. You can recognize an owner of that sharp knife by "the bald patch of glory" on his forearm.
Shave without touching the skin, cutting hair at the base of the strand. Becomes possible at 40-50 BESS or about 0.1 micron edge.
Such a knife is not just shaving sharp, it is razor sharp.
Tree topping – where you can run the edge down above the skin and cut free standing hairs in the middle.
I spent an hour maybe to precisely determine the edge width capable of top trimming. After I ran out of forearm hair, I turned to my thighs, and funnily enough discovered two gradations:
- tree-topping on the leg is achieved easier, at 35-40 BESS;
- tree-topping on the forearm requires sharpness under 0.1 micron, 25-30 BESS.
With a knife that sharp you can smooth shave your face without pulling on the whiskers.
Hanging Hair Tests
Human hair cuticles average 0.3-0.5 micron in thickness layered like roof shingles. Cutting edge must be within this range of thickness to penetrate between them.
Due to the fact that there are up to 10 layers of cuticles, it is possible not only to split the hair lengthwise, but also whittle curls off a hair.
The test is performed with the edge angled to the root side of a hair for the edge to catch between the cuticles, at about 2cm out from where your fingers grip the hair.
Violin sign - the hair doesn't cut, but it "plays violin" with the edge.
This is due to the hair cuticles catching the edge, which is not sharp enough to penetrate. You can sense the violin-like vibrations, and with certain blades even can hear a faint ringing sound.
I’ve been testing edges over and over again at 10 BESS steps until firmly determined that your knife starts playing violin at 115 BESS or 0.2 micron.
This one is a highly precise test.
From this point you are ready to delve into the true razor-sharp level, not just shaving-sharp.
Cut a free hanging hair - becomes possible at 70 BESS or 0.15 micron.
You cannot split the hair yet, but already can slice it. Note that at this stage it is not a popping cut, you have to slice the hair.
Split hair - the edge catches the hair between cuticles and splits it lengthwise.
60 on BESS scale is where the edge starts splitting a hair.
![[Image: Hair_splitting.JPG]](http://knifegrinders.com.au/photos/Hair_splitting.JPG)
Hair popping - the severed hair part will jump away as soon as it touches the edge.
Requires at least 30 BESS or under 0.1 micron edge. I couldn’t make hair pop with 35 and 40 BESS edge.
Whittle hair (cut curls off a hair) – becomes possible at 25-30 BESS.
![[Image: Hair_whittling.jpg]](http://knifegrinders.com.au/photos/Hair_whittling.jpg)
Silent slicer - at 20 BESS or under the hair falls effortlessly as soon as it touches the edge; not jumping away like with popping, just silently falls.
And finally, Tongue test – a sharp knife tastes like metal, and really sharp like blood.
Australian Knife Magazine is a printed magazine, and I seriously doubt anyone in the US will ever have a copy unless I send them, but I won't.
I therefore thought making this data available to the BESS forumers.
Knife community uses a set of fanciful terms to describe sharpness.
These terms, although not academically endorsed, are full of meaning as they come from real life, flesh and blood cut off our fingers.
They may sound vague and not clearly defined, but are discriminating enough for us. We readily distinguish a work sharp edge from shaving sharp, and will never confuse a scary sharp knife with crazy sharp.
Sharpness reflects the very edge itself, not overall performance of a knife, which is subject to cutting tests and not discussed here.
On the one hand, we have our informal classification of sharpness, like working edge - sharp edge - fine edge etc (I am listing the full terminology in a paragraph);
on the other hand, we have a set of tests telling us how sharp the knife is, like thumb pad test - fingernail test - shaving test etc, and again I will give a complete list of these tests further on as they are so inventive that can capture imagination.
Armed with a BESS PT50 edge sharpness tester and a few hundred knives from our rental pool and my collection, started I my study, full of curiosity and apprehension.
DEGREE OF SHARPNESS
Dull - an edge over 500 BESS.
Butter knife is a classic example of ultimate dullness.
Plastic knife from the last Sydney Knife Show cafe scored 1750 BESS;
Plastic knives they give us at airlines are 2000+ BESS.
An edge over 500 on BESS scale requires sharpening.
Sharpness in the range of 200-400 BESS.
Working edge, real world sharp is within 300-450 BESS.
Sharp we call an edge at 250-300 BESS. Quality cutlery out of the box comes that sharp.
Very sharp - most people consider it an edge between 130-200 BESS.
Fine knife edge takes us to the quarter of a micron level, 100-150 on BESS scale.
Shaving sharp - edge starts scraping shaving at 160 BESS - and we will discuss all the gradations in the Sharpness Tests section later.
Nuts sharp referred by knife lovers is an edge at 0.2-0.3 micron, 100-150 BESS.
Scary sharp edge is at 0.2 micron or scores 100 BESS.
Further to the submicron level, under 100 BESS, we start talking of keenness rather than sharpness.
Not many people have the skill, knowledge, or equipment to reproduce this edge.
Crazy sharp starts just under 0.2 micron, from around 90 BESS.
Razor sharp – for example, a double-edge Schick razor from Woolworths is 30 BESS.
Knife edges in this range have insane-this-should-be-illegal levels of sharp.
Wickedly sharp is a term reserved for edges under 0.3 micron, which is less than thickness of a human hair cuticle.
And finally, esoteric sharpness.
A silk scarf dropped on the edge cuts in half by itself.
Sharp enough to shave a gnat’s ballbag.
SHARPNESS TESTS or HOW TO KNOW HOW SHARP IS YOUR KNIFE
Now that we have the edge sharpness tester from Mike, these tests are no more than historical for me, but I will always be feeling sentimental about them as they've been the only means guiding my sharpening for decades.
Values I give further is the earliest attained sharpness (from the dullness end of the range) when the test can be performed cleanly.
Thumb Pad Test - feeling the edge crosswise with the ball of your moistened thumb. Draw your thumb across, not along, the edge to feel how it grips into your thumb print. If the edge tickles your thumb the knife is not dead dull. This is a widespread belief; our tests, however, show it is false.
Just today an electrician brought me his knife to sharpen, which scored 795 BESS, yet it still tickled my thumb.
Too subjective to be a useful test.
Fingernail Test - resting the edge with its own weight on your nail check if it catches. When it sticks, it is sharp. If the edge glides over your nail, it is dull.
I’ve tested a dozen of knives from 800 BESS edge down to 200 with a 50 BESS step to determine the catching point, and the fingernail test becomes positive at 350 BESS.
This one is a truly useful test as it tells you have a working edge.
Whittles soft wood (e.g. pine) – becomes positive at 150 BESS.
This is shaving range, which has a number of well-defined gradations that we will discuss at great length after the paper tests.
Paper Tests
Roughens & tears paper – a knife starts tearing paper at 600 BESS, not duller.
Obviously, such a knife requires sharpening.
Slices 80gsm printer paper – a knife can do it at 450 BESS, which is the upper limit of the working edge.
Not a very clean cut initially, but already effortless; the sharper the edge the cleaner the cut.
Slices newsprint – this is somewhat more demanding, and indicates an edge within a good working range, at minimum 400 BESS.
Slices a sales docket/receipt – as these dockets are very thin, the test is even more demanding for sharpness, and becomes positive at 300 BESS.
When positive, this test takes the edge from just working to sharp.
Filleting printer paper, i.e. shaving off layers of 80gsm paper not cutting through, first demonstrated by Sal Glesser in his Spyderco Sharpmaker video.
I’ve tested a good dozen of knives slightly differing in sharpness to precisely determine how sharp must be an edge to be able to shave paper – at 130 BESS or a quarter of a micron.
Pretty sensitive and precise test, indicating a very sharp fine edge.
Only knife that sharp will cut a circle in light printer paper.
Toilet paper test - push through then slice down a single ply toilet paper. Possible at 50 BESS.
The main challenge of this test I found was to harvest that single ply. Unfortunately, nowadays this test is losing its standardization power since the test media is losing the line of distinction with the facial tissue.
Shaving Tests
Scraping shaving – a toothy edge is capable of catching hairs on the skin, but instead of cutting them it “rips” them out of your skin: 160 BESS or about 0.3 micron.
Shave against the skin - won't shave arm hair above skin, but shaves touching the skin without trouble.
This test has two gradations:
- with the grain of hair – 140 BESS; and
- against the grain, which requires way better sharpness in the vicinity of 0.2 micron, 95-100 BESS.
This is the level of sharpness the knife community refer to as “nuts” and “scary sharp”. You can recognize an owner of that sharp knife by "the bald patch of glory" on his forearm.
Shave without touching the skin, cutting hair at the base of the strand. Becomes possible at 40-50 BESS or about 0.1 micron edge.
Such a knife is not just shaving sharp, it is razor sharp.
Tree topping – where you can run the edge down above the skin and cut free standing hairs in the middle.
I spent an hour maybe to precisely determine the edge width capable of top trimming. After I ran out of forearm hair, I turned to my thighs, and funnily enough discovered two gradations:
- tree-topping on the leg is achieved easier, at 35-40 BESS;
- tree-topping on the forearm requires sharpness under 0.1 micron, 25-30 BESS.
With a knife that sharp you can smooth shave your face without pulling on the whiskers.
Hanging Hair Tests
Human hair cuticles average 0.3-0.5 micron in thickness layered like roof shingles. Cutting edge must be within this range of thickness to penetrate between them.
Due to the fact that there are up to 10 layers of cuticles, it is possible not only to split the hair lengthwise, but also whittle curls off a hair.
The test is performed with the edge angled to the root side of a hair for the edge to catch between the cuticles, at about 2cm out from where your fingers grip the hair.
Violin sign - the hair doesn't cut, but it "plays violin" with the edge.
This is due to the hair cuticles catching the edge, which is not sharp enough to penetrate. You can sense the violin-like vibrations, and with certain blades even can hear a faint ringing sound.
I’ve been testing edges over and over again at 10 BESS steps until firmly determined that your knife starts playing violin at 115 BESS or 0.2 micron.
This one is a highly precise test.
From this point you are ready to delve into the true razor-sharp level, not just shaving-sharp.
Cut a free hanging hair - becomes possible at 70 BESS or 0.15 micron.
You cannot split the hair yet, but already can slice it. Note that at this stage it is not a popping cut, you have to slice the hair.
Split hair - the edge catches the hair between cuticles and splits it lengthwise.
60 on BESS scale is where the edge starts splitting a hair.
Hair popping - the severed hair part will jump away as soon as it touches the edge.
Requires at least 30 BESS or under 0.1 micron edge. I couldn’t make hair pop with 35 and 40 BESS edge.
Whittle hair (cut curls off a hair) – becomes possible at 25-30 BESS.
Silent slicer - at 20 BESS or under the hair falls effortlessly as soon as it touches the edge; not jumping away like with popping, just silently falls.
And finally, Tongue test – a sharp knife tastes like metal, and really sharp like blood.
http://knifeGrinders.com.au
