Thread: Standard Reference Material for Hanging Hair Test

Thanks for pointing out the typo, which I've fixed in the posting.

Actually, you yourself are making a type of "all or nothing" argument here: "what you end up with is a test of how well razors cut a piece of filament. It doesn't necessarily translate to a test of shave readiness... But, it still doesn't translate to a test of shave readiness..."

This is equivalent to saying something like: "If you don't measure ALL of the variables involved, you won't get ANYTHING (i.e., NOTHING) useful from the test." This is fallacious. The answer is not a dichotomy: all or nothing. It is a trichotomy: all, something or nothing. So this sets up a "straw man" that is easily demolished by simple rhetoric. No, it doesn't necessarily translate into a test of shave readiness. But, equally, it doesn't necessarily NOT translate into a test of shave readiness either.

So the real question isn't "If razor PASSES the FCT, that doesn't necessarily mean it's shave-ready.". The important question is the reverse: "If the razor FAILS the FCT, what does this mean about about shave-readiness?" If it means SOMETHING, then it is useful. The opposite of ALL is not NOTHING.

Others have voiced or referred to similar arguments:

"That an even unreliable HHT to determine 'Sharpness' has never been a question, that it has nothing to do with 'Shave Readiness' has always been the debate." Again, the idea that the opposite of "all" is "nothing".

"... so even if you can prove you've gotten the sharpest edge out of a razor with numbers, I am still not willing to accept this as a well honed edge until I have shaved with it." The implication is that verifying sharpness is worth nothing. But what if you verify dullness?

I am not suggesting that shaving is not a good test for a particular person of "shave-readiness", even though the measurement is subjective, skill sensitive, idiosyncratic and time unstable. Certainly it is the endpoint outcome of primary importance, so it is the objective of all of this. I am not also suggesting that "shave-readiness" is not a happy conjunction of multiple important variables, some of which are person idiosyncratic and some of which are razor idiosyncratic. Sharpness alone is probably not completely sufficient (others might be bevel angle, shaving angle, type of steel, type of hair, growing angle, microstructure of edge, etc.), but I am sure it's probably at least 80% of the issue. Otherwise a commercial disposable razor or blade would be a flop.

If you make a measurement, it is useful if it correlates with the desired outcome. It doesn't have to correlate perfectly. It only has to correlate enough to be useful.

If the FCT didn't correlate at all with my subjective opinion, I wouldn't continue with it. But so far it has near 100% correlation for me. It also correlates fairly well with my HHT. These are both promising.

However, I am open to the possibility that, once basic good sharpness occurs, then sharpness may no longer correlate with improvements in shaving. Those might relate to other factors. This would also explain the division into camps on SRP. For beginners, attaining initially useful level of sharpness is difficult, so sharpness is the central issue. Thus the HHT interest. For experts, all razors used are very sharp, so very small improvements in sharpness are no longer correlated with significant improvements in shaveability. Something else is going on.

The key question is then: "If two razors differ detectably in sharpness, do they also differ detectably in shaveability, or is this only true for some range of sharpness?"

As an empiricist, I await the outcome of further experimentation. From the results I'll see where the usefulness of the FCT starts and ends.