OK, I lied. My last post was not my final post on shaving.
To complete the analysis of factors affecting razor blades, I need to document normal variation in beards. In short: It’s huge. All other things equal, that almost certainly leads to huge variation in razor blade life.
This scholarly article will probably tell you more than you ever wanted to know about beard hair. A key sentence is:
The density of beard hair follicles varies with facial area and ethnicity. Values range between 20 and 80 follicles/cm2
I interpret that to mean that, within normal variation, some guys have four times as many beard hairs (per skin area) as others. All other things equal, that’s going to generate four-fold variation in razor blade longevity.
There is further variation in hair thickness, stiffness, shape, and so on.
With that much background variation, there really is no such thing as normal razor blade life. There’s only what’s normal for you, and what you can plausibly do to extend it.
The only shaving technique studied in that article is wetting (hydrating) your beard. Which I think anybody who shaves with a blade understands to some degree.
The force needed to cut a beard hair is reduced by about 20% within the first minute of water contact. After four minutes, the cutting force is reduced by 40% and does not significantly decrease further with longer hydration
This correlates well with the standard advice you’ll hear from shaving experts, which is to let your shaving soap or cream sit on your face for a minute or two before you shave. (Both shave cream and soap lather contain water.)
Interestingly, I can find zero scholarly evidence that the fat (e.g., stearic acid) in shaving cream does anything to soften hair. And yet, I have found that shaving cream extends blade life, compared to shaving with soap, even though both methods result in hydrating the beard prior to shaving. Moreover, so far (shave #10 on the same blade, today) it extends blade life far beyond what you might expect from the 40% reduction in cutting force cited above. And, all major brands of shaving cream or gel contain one of two fatty acids as their main component.
Maybe that’s strictly a skin softener? Maybe a lot of the wear-and-tear of shaving comes from the skin, and not the hair?
Beats me. Whatever the underlying mechanism is, it seems to work. And every manufacturer of shaving cream seems to include it as the main ingredient after water.
I guess, now, I really will call it a day on posts about shaving.
That’s not to say that I’ve exhausted the topic.
It’s more than I’ve exhausted my willingness to track down all the nutty claims that are made about shaving and razor blades. Every time I look, I find another one. Today, it’s a patent claiming that dipping razor blades in 12% to 20% citric acid will extend their life at least five-fold, by preventing the formation of “mineral crystal buildup”.
Edit: Well, as it turns out, upon further research, that’s not so nutty after all. See Post #1699 on how water spots (calcium carbonate deposits, or “mineral crystal buildup”) can coat the razor edge and so dull the blade.
Let us never forget that you can keep your blades sharp forever by keeping them in a pyramid-shaped object. But only if you orient it exactly with the earth’s magnetic field. And yeah, there’s a patent for that one, too.
