Thumb nail test

[Nix]

My grandfather taught me a variant of the Thumb Nail Test, and a barber once taught me the thumbnail test to use when checking to see if a razor was "shave ready". This barber has a couple decades of experience and a very nice straight razor collection himself.

In a different thread, a member asked about checking his razor to see if it had been 'dinged' by some incidental metal-on-edge contact. One of my suggestions was that he try the Thumb Nail Test to feel for a ding or chip. A couple of other senior members spoke up quickly and--in no uncertain terms--strongly advised against using the thumb nail test.

I didn't want to derail the OP's thread, but did want to hear more about why one should not use the Thumb Nail Test.

I have used the thumb nail test many time to check a knife's edge. Just yesterday I discovered that my Sebenza pocket knife has a small flat spot on the edge using the Thumb Nail test. I have--on my barber's advice--used it to check my razors on a couple of occasions. But, and this may be a factor, after using the Thumb Nail test, I always strop the edge again.

However, in the interest of science, a couple of days ago I decided to sacrifice my face in the pursuit of knowledge and truth and test the deleterious effects of the Thumb Nail Test:

I have a new Boker Edelweiss razor that had been used 3-4 times. Each time it was used it was stropped both before and after the shave. For this test, I stropped the razor as is my custom (linen and leather). I then performed the Thumb Nail Test three (3) times. The razor felt sharp, smooth on the nail, a little bite. Two of the tests were done on the top of the nail, the third was done on the leading edge of the nail (Grandfather's variant).

After nail-testing the razor, I did NOT strop it as I would normally do. I proceed to do a quick prep with face wash, hot towel for ~ 1 min, and then some Trufitt & Hill Lime shaving cream.

And then I shaved...with some trepidation.

The shave went well; whiskers were severed; and I was deemed to be appropriately groomed for work by my better half. I did manage to nick myself under the chin, but this was attributed to operator error and not the razor itself (I've been straight razor shaving since mid-Sep, and while my skills are improving, not an expert by any stretch.) Overall a satisfactory shave, but the blade didn't seem as fiercely sharp as my Dovo when I first got it from SRD.

Later that day I did a hanging hair test of the razor...and it failed. Completely. The problem here is that I didn't think to do a hanging hair test on the razor before and after the Thumb Nail test as well, so there is no baseline hanging hair test for comparison.

I apologize for my poor test design, but at the end of the day, I can't say that the Thumb nail test destroyed my razor's edge. In fact, I stropped it on linen & leather the following day and shaved with it again in a completely satisfactory manner.

My question to the community is, if hair and nails are both made of keratins, what is the downside to doing a Thumb Nail test on a razor, especially if one can strop it before use?