Measuring blade sharpness: Does it tell us anything about shaving performance?

[Spang]

Many of us have seen the blade sharpness testing over at Refined Shave. My first observation is that I really appreciate the effort this gent has put into his attempt to objectively measure the sharpness of blades, since there is really no comparable data set out there that I know of. And god knows we won’t ever get this type of technical information from the manufacturers, if that is even possible.

But when I compare my (admittedly subjective) experience with the measured data at RS, I have to wonder if the basic metric he is using for sharpness accurately translates into shaving sharpness. While it is true that “numbers don’t lie”, they only inform about whatever characteristic is being measured. If the numbers are a measurement of something that doesn’t correlate directly to performance, then they don’t really tell us anything we can use.

I’m not an engineer or materials scientist, so I can’t make an informed assessment of the methodology used to make the measurements. From what I understand there is no accepted standard for “sharpness”. The test used by RS is basically a function test, i.e. how much force is required to cut something. I’m hoping some of our more learned members can weigh in on the validity of this as a measuring method.

One observation I would make regarding the RS methodology: it appears that the sharpness measurements are made and recorded first, and then the subjective “shave test” ratings are observed and recorded. Interestingly, the subjective shave test ratings appear to be 100% congruent with the measured data, i.e. the blades that initially measure sharper, from what I can see, always rate better in the subjective observations than the less sharp blades. That seems like a red flag to me. I’m not implying that the subjective ratings are intentionally cooked, but perhaps this is a case of confirmation bias?

 

[ajduplessis]

Only way to measure is to shave. If it’s smooth and close it’s good, If it’s not grab something else...

 

[Ron R]

I have been wondering about sharpness also, also I believe the Gent over at Refined Shave uses them for head and face shaving and gives his opinion on the shaves. That set aside a very sharp blade can be a weaker blade because of the thin angle it is ground and honed to so when used it can deteriorate quickly. So for 1 or 2 shaves it will perform possibly well and then quickly drop off. Feather blades are known for their sharpness but they are not as smooth as others. So if you gain in sharpness you have to give up another part of blade for that charteristic. But what feather did do is make razors that are milder so when you use their blade you get a nice shave. I have FHS-10 blades for my Oneblade Core and the 1st shave is excellent but it drops off fast, But I use a Gem Personna blade that is very sharp in the same razor but I can get 10 + shaves out of it so the metal make up is different + Gem Personna has been making blades of over 100 yrs and their proprietary metal composition is their signature of perfection .
Have some great shaves!

 

[TexOkie Shaver]

I use Feather blades exclusively, having decided a couple of months ago that it was either the Feather or the BIC. The data at RS pointed to the BIC as the better blade in the long haul, but with so many negative comments on the BIC, I couldn’t help but wonder if my experience with them was an anomaly or perhaps everyone else were for some reason getting sub par blades. I decided not to chance the BIC blades and go with the Feather blades and purchased 300 when I found a good price.

As it turns out, my decision was probably clouded by the data at RS. My experience lately with Feather blades is that they do a great job way past 3 or 4 shaves. My last blade had 20 shaves on it when I binned it. The only reason I binned it was I suspected this was an exceptional blade and I wanted to start over with a new blade to see if I could repeat the results. The new blade was sharper, but not any more efficient. After 12 shaves on that blade, I’m still getting great close shaves.

My takeaway on this is that technique is far more important than sharpness. I suspect I could get the same results with a lesser blade, so I’m back to thinking I should have bought 300 BIC blades at an even cheaper price.

But, what’s done is done. I have enough blades to last the rest of my life if I get 20+ shaves on each blade.

 

[McBlade]

In my experience, real-world results compare very well to the measured sharpness.

Some blades can vary quite a lot between shaves. It's also nice to get some information about consistency.

 

[Eben Stone]

I like metrics, and take a semi-scientific approach to "testing" my shaves, so I find his charts very interesting.

However, I have a serious problem with comparing his pure sharpness tests to real world shaves. I'm sure he's testing very scientifically, but it's hard to know how this information would translate to real world shaves, because he does not mention what angle the blade is mounted at compared to the fake whisker material, and he doesn't mention if the blade is parallel or slanted compare to the cutting direction, and he doesn't mention the mount's clamping distance from the blade's cutting edge (how much is the blade allowed to flex, if any, and this is especially important for the blade's angle, which isn't mentioned). If he does mention this information then I certainly missed it.

No one shaves at a 0° angle, and I dont know about anyone else, but I certainly don't hold the razor so it's angled the same as the stroke direction (I fake a slant by using the Gillette slide, and J-hooking). So maybe a blades sharpness in his rig against his fake whisker material, may not translate equally to a real world shave.

According to some articles quoting info published by Gillette, shavers are not able to accurately determine the sharpness of a blade, and mis-interpret tugginess for a dull blade. I'm not sure I agree with that, but according to Gillette the tugginess is reduced my a blades coating not its sharpness.

 

[Mouser]

The best blade evaluation I've seen is the one by G.D. Carrington over at a different
shaving site. I don't know if its allowed to say but if it isn't i guess it will just get deleted. It's posted at Shavenook at the head of the Blades sub forum. But blades are the most ymmv part of our thing and the best advice I can give is find out for yourself

 

[psfred]

Edge acuity, sharpness, and shaving feel are not directly related, as Gillette discovered back in the 1950's. All modern razor blades, minus occasional equipment or quality control failures, are highly polished with fine edges, probably within the capability of the steel. So far as I know, all the blades manufactured today are made on highly computerized automated machinery.

Friction as the hair is cut produces most of the "feel" of shaving, and that is most likely determined by the texture of the blade bevels, the amount of contact area (determined by bevel angle) and the surface composition of the bevel for the distance the hair will contact it (coatings and base steel).

All modern blades have a PTFE coating at least, and nearly all of them have other coatings as well, notably these days diamond like carbon. These coatings contribute to comfort (lack of friction as the hair is cut) and wear resistance.

It's not a simple matter of how fine the edge of the blade is.

 

[Spang]

It's not a simple matter of how fine the edge of the blade is.

Thanks for this, it makes sense. Is it your opinion that the testing at Refined Shave is measuring how fine the edge is?

 

[Spang]

I'm sure he's testing very scientifically, but it's hard to know how this information would translate to real world shaves

Yeah, that's really my question as well. I agree, the data seems to be based on relatively consistent and repeatable methods and the reporting looks to be statistically sound. So, he's doing a consistent job of measuring something, but I'm not sure that something correlates to shaving performance. My personal (again, subjective) experience suggests otherwise.

 

[Invicta]

So, he's doing a consistent job of measuring something, but I'm not sure that something correlates to shaving performance.

He is measuring a perceived shaving performance but that has many other variables. Sharpness on its own is not the only parameter that determines a good performing blade and smoothness has to be a consideration too, hence all the different coatings used.

 

[AimlessWanderer]

There is no real consensus on anything in the world of traditional shaving. Something either works for you, or it doesn't, and attempting to throw science at it achieves nothing.

We all differ greatly in our skin and hair types, in our grain flow maps, and how perpendicular or parallel to the skin our hair grows. Our water chemistries differ, as do our brush construction, an our ambient temperatures an humidity. Our techniques evolve differently, depending on the factors already covered, who (if anyone) we learned from, and the kit we started with.

Edge geometry, and how refined that edge is, are just further variables in that vast ocean of uncertainty. Coatings and metallurgy variations muddy the waters even more. Furthermore, as many of us will confirm, if you change one thing, you change everything. We find certain brushes working better with certain soaps, certain razors favouring certain blades, but the certainty that someone else will reach the same conclusion is virtually nonexistent.

Many people, here and elsewhere, have tried to "prove" X is better than Y. It's farcical because of all the myriad of variables, and unhelpful as it may steer people away from their best shaves, instead of towards them. Even people's own findings change as the seasons cycle through, and the beard and skin ages, or their technique evolves, and organic ingredients vary from one batch to the next.

The only thing that's certain, is that someone somewhere, will have good cause to disagree with everything. Everything! Including this post.

 

[MikeTbass]

Thanks for this, it makes sense. Is it your opinion that the testing at Refined Shave is measuring how fine the edge is?

I'll chime in here : what's being measured is the force necessary to perform the cut. How finely honed, or polished, the edge may be is a factor but bevel angle and thickness also come into play. Imagine sharpening a thick splitting axe to a hair shaving finish and then chopping some carrots; now imagine doing the same with an unsharpened thin stock of sheet metal. You will potentially be able to perform the cut with both methods but the edge refinement is very different. In this hypothetical example the axe is much "sharper" but the thinner sheet metal has less material behind it's unsharpened edge to move through the cutting media. This results in potentially less force to perform the cut with a much less sharp edge.

The above example is a rather extreme depiction of what may transfer to shaving blade performance, but the point is that edge refinement (what many call "sharpness") does not directly translate to cutting performance. Thinner blade stock and shallower bevel angles can greatly increase cutting performance as there is simply less material to wedge through the item being cut. When I think of how a DE blade performs in a razor I imagine that the honing angle, blade coating and edge refinement all factor in to how sharp a blade is perceived to be. To hazard a guess I'd say most every DE blade is more than "sharp" enough from an edge refinement standpoint and honing angle is the more prominent variable.

Feather blades, for example, I would believe to be honed at a shallower angle to improve cutting performance. This is perhaps why they are so sharp out of the box but degrade quickly - less blade stock behind the edge decreases edge stability and results in edges that damage easier. This is not something I have any proof of but is merely a pondering using my experience in cutlery to explain what I see with DE blades.

In summation, there are many more factors that dictate cutting performance than just edge refinement. Over the holiday weekend I got to experience many other folk's cutlery and every house has a "good knife" that is "sharper" than the rest. Many of these are not actually that sharp at the edge but use a combination of thinner blade stock, shallower edge geometry, and various get-arounds that are perceived as "sharp" by your average user.

 

[BigJ]

...what's being measured is the force necessary to perform the cut. How finely honed, or polished, the edge may be is a factor but bevel angle and thickness also come into play.

.. there are many more factors that dictate cutting performance than just edge refinement.

Over the holiday weekend I got to experience many other folk's cutlery and every house has a "good knife" that is "sharper" than the rest. Many of these are not actually that sharp at the edge but use a combination of thinner blade stock, shallower edge geometry, and various get-arounds that are perceived as "sharp" by your average user.

+1! Great discussion and some excellent points!

Objectively, one can measure force needed to cut. But, many subjective factors determine shave quality!

Your cutlery example is great! I have many knives, mostly stainless that get put out and used because they work and look fine. BUT, when I have to really ‘carve’ a roast or turkey my decades old Sabatier carbon steel knives come out! They stain but keep a very sharp edge and are a total pleasure to use!

 

[Spang]

I'll chime in here : what's being measured is the force necessary to perform the cut. How finely honed, or polished, the edge may be is a factor but bevel angle and thickness also come into play. Imagine sharpening a thick splitting axe to a hair shaving finish and then chopping some carrots; now imagine doing the same with an unsharpened thin stock of sheet metal. You will potentially be able to perform the cut with both methods but the edge refinement is very different. In this hypothetical example the axe is much "sharper" but the thinner sheet metal has less material behind it's unsharpened edge to move through the cutting media. This results in potentially less force to perform the cut with a much less sharp edge.

The above example is a rather extreme depiction of what may transfer to shaving blade performance, but the point is that edge refinement (what many call "sharpness") does not directly translate to cutting performance. Thinner blade stock and shallower bevel angles can greatly increase cutting performance as there is simply less material to wedge through the item being cut. When I think of how a DE blade performs in a razor I imagine that the honing angle, blade coating and edge refinement all factor in to how sharp a blade is perceived to be. To hazard a guess I'd say most every DE blade is more than "sharp" enough from an edge refinement standpoint and honing angle is the more prominent variable.

Feather blades, for example, I would believe to be honed at a shallower angle to improve cutting performance. This is perhaps why they are so sharp out of the box but degrade quickly - less blade stock behind the edge decreases edge stability and results in edges that damage easier. This is not something I have any proof of but is merely a pondering using my experience in cutlery to explain what I see with DE blades.

In summation, there are many more factors that dictate cutting performance than just edge refinement. Over the holiday weekend I got to experience many other folk's cutlery and every house has a "good knife" that is "sharper" than the rest. Many of these are not actually that sharp at the edge but use a combination of thinner blade stock, shallower edge geometry, and various get-arounds that are perceived as "sharp" by your average user.

Thanks very much for taking the time to post this thoughtful reply. I understand a little about blade geometry, but your explanation really helps to understand how this applies to razor blades. Your cutlery analogy is very helpful in understanding the importance of honing angle and thickness behind the edge on overall cutting performance.

 

[Ron R]

I use a lot of Gem blades and some Schick injector blades and the Gem Personna SS PTFE(teflon coated) blade is very sharp & stronger that is .009 thickness(DE blades .0035 thickness) and has a 3 facet edge that resembles a surgeon scalpel edge. I think they are just as sharp as a Feather blade IMO but are designed to last a little longer because of their grind and honed stropped edge and their cutting action angle direction.
Gem or Personna injector blade grind 3 facet profile in picture below.

Have some great shaves! Stay and think safe in these times!

 

[TexOkie Shaver]

I use a lot of Gem blades and some Schick injector blades and the Gem Personna SS PTFE(teflon coated) blade is very sharp & stronger that is .009 thickness(DE blades .0035 thickness) and has a 3 facet edge that resembles a surgeon scalpel edge. I think they are just as sharp as a Feather blade IMO but are designed to last a little longer because of their grind and honed stropped edge and their cutting action angle direction.
Gem or Personna injector blade grind 3 facet profile in picture below.
View attachment 1188123View attachment 1188124
Have some great shaves! Stay and think safe in these times!

When you ride the cap on a DE razor, what do you figure the angle of attack is?

 

[TexOkie Shaver]

It should be approx 25 to 35 degrees depending on cap shape, I have a Wunderbar slant but the blade is curved so much you almost are riding the bar more IMO ( handle direction is more in ridding the bar angle).

I’m using a Rockwell 6S. It’s cap isn’t as thin as some, but not as thick as many others. I was thinking that by using the 6 plate I could lower the angle, but now I’m not so sure. Everything is so small in there it’s almost impossible to measure.

 

[Furex]

There is some good information in this wiki article:

Science Of Shaving

State of the Art of the ScienceP&G Research

www.badgerandblade.com

the blades that initially measure sharper, from what I can see, always rate better in the subjective observations than the less sharp blades. That seems like a red flag to me. I’m not implying that the subjective ratings are intentionally cooked, but perhaps this is a case of confirmation bias?

Refined Shave was a great resource for objective sharpness testing, and it would have been cool to see it continue.

However, it makes no attempt to separate the subjective impressions from pre-existing information and its priming effects, smoothness is only measured subjectively, and reviews seem to be based off a sample of very limited size, possibly resulting in a large margin of error.

Also:

• the blade is also used to shave his head, adding a confounding factor but essentially no extra usable information.
• blade performance can drop without any use. Hence, things like time between shaves and its variability, the conditions in which the blade is stored may also lead to appreciable changes in its sharpness or other metrics.

BTW there are other attempts to quantify razor blade objectively, most typically through SEM photography to observe the blade edge, its geometry and conditions, etc. IIRC, even though science of sharp is focused on straight razors, there should be some data on Feather disposables. Sharpologist has been using SEM, too.

 

[Chandu]

Sharpness is but one factor. For me there is sharp enough and not sharp enough. How well the shave is beyond that depends on the how it is ground, how the razor holds it, how I hold the razor and so on.