Way back in October 2009, ShavenMaven introduced a thread about possible differences in DE blade width and how that could affect the "aggressiveness" of certain blades:
He measured some with a digital micrometer and found differences that correlated with his shaving experience. I read this and entertained some doubts.
In any case, if there were a lot of variation in blade widths, it could create havoc with my photo analysis of razor geometries:
I did use just one blade for that out of caution, but expected to see similar results with other blades too.
He asked others to measure theirs. But it didn't seem to go anywhere. So I wondered how to do this better, since any measuring tool that has to touch a flexible blade has a high potential of altering the measurement! I decided that optical was best - no impact. But how?
I had a 25 power field microscope with a reticle.
The field was too narrow to take in the entire blade...
but you'd get terrible parallax errors if you could anyway!
So had to compare against something else.
I arbitrarily picked a Plain Jane old Schick blade as a measurement standard.
I placed the blade of interest on top but offset a bit laterally.
I aligned the left side carefully against a uniform plastic blade box.
Then compared the right sides.
If the inspected blade proved to be wider, I put the Schick on top.
Then measured the difference (if any) where they overlapped.
Trickier than it sounds, because you've got to adjust focus and get the subject edges right in the center to prevent parallax.
So, I couldn't help but notice other things about the edges as I went along (yes, there's a nice old thread with microscopic photos but the pictures have mostly vanished). Anyway, here it all is in a chart:
ShavenMaven was happy with his Crystals, but thought maybe the Derby extended farther, and the Shark even more so - based on micrometer measurements. And found them a bit harsher.
Looking at the table, it's the Crystals and Personna Reds that appear to be out of line. These two are suspected to be made in the same Israeli factory by the way - although the Reds are quite mysterious and perhaps greymarket. All the rest of the modern blades clock in at the same width, within the measurement accuracy of 0.05 mm.
Two of the older blades I have are out of line in the other direction. All the rest appear quite uniform. The Herder and Blu Strike, by the way, are the crudest blade edges I've ever seen. The oldest Gillettes are remarkably finely ground. The later Blue and Super Blue, once renowned, seem surprisingly poor in comparison.
Bear in mind that, if there were a 0.05 mm difference in total width, the impact on blade exposure would be on the order of 25 microns. A human hair is around 100 microns, just to put this in a beardly perspective. The observed differences were closer to 50 microns, just where it could start to mean something.
Particularly interesting are the different characteristics of the edges. One of the Gillette three-holes and one of the NEWs I examined appeared to have an extraordinary fine polish to the edge...but then I wondered if that wasn't aftermarket. My dad used to use one of those Twinplex DE stropping machines every morning. So these blades could have got their polish that way. I'll have to look at the rest of my old blades to see if there's variation.
Of the current blades, real differences here.
A fun mind game:
Pretend I've never used any of them and rank them on how I'd expect them to shave, based on appearance of the edges alone. Here's what I'd come up with.
Best whisker shearers
Feather because of the short, nicely executed secondary bevel with very high polish; and Iridium because of the extremely short secondary bevel and fine grind.
Better than average
Astra because of the well-executed single bevel (but losing points because grind is average); and Shark for the nice polish on the tertiary bevel, but losing points for having three in the first place.
Worst whisker whacker
Merkur because it has three bevels and all of them suck.
The Israeli blades (blue and red) because they project a bit less from a given razor.
With the rest falling somewhere in a middle ground. Of the above, I haven't got around to the Iridium yet, but have used the rest. The red Israeli Personna for the first time on Monday (it pulled, but I'd come off two weeks of Feathers so will give it more chances).
All the above ignores nice and important stuff like alloys, heat treatment, coatings etc. but it's interesting how visual apprehension aligns with experience. YMMV and all that...