Thread: Thumb nail test

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?

Interesting post. My take would be that with the thumb nail test you're actually interfering with (blunting) the bevel and so, need to reset it prior to polishing. Hair and nails may be made of the same stuff, but they're not the same thing.

you say it did not feel as sharp as your Dovo. Did it feel as sharp after the TNT as it did the 3-4 shaves prior to it?

Originally Posted by pcb01

you say it did not feel as sharp as your Dovo. Did it feel as sharp after the TNT as it did the 3-4 shaves prior to it?

I did not notice a significant difference.

I used the Boker the day prior to doing my Thumb Nail Test testing and I cannot say it shaved better before the Thumb Nail test than it did immediately after. But memory can be fallible. Certainly the post-Thumb Nail testing shave did not strike me as significantly worse or more difficulty than the shave I had had with the same razor before subjecting it to the Thumb Nail test. But, pardon the pun, I won't split hairs over whether it was marginally duller or not after the Thumb Nail testing.

I referenced the Dovo because it seemed, fresh from a professional honing by SRD, to be the sharpest razor I have used to date.

With additional stropping, the Boker did pass the hanging hair test and shaved well, but, again, maybe not to the same degree as my Dovo. (My favorite razor is a Hart, and that doesn't feel quite as sharp as the Dovo did either. Obviously the Dovo really stands out in my memory.)

I also tried the Thumb Pad test, but I don't have enough experience with this test to judge the sharpness of a blade well.

While I agree that thumb nails and hair are different things entirely; I don't know that thumb nails are significantly harder than hairs. There are several different forms of keratin, and nails may indeed be harder, but could there be that much of a difference? I doubt that a toothpick is significantly harder than the trunk of the tree from which it was made, although the toothpick is clearly easier to cut. I am under the impression that it is the hardness of a material that determines it's ability to cut and be cut...and to cause wear, other variables being equal.

Originally Posted by Nix

My grandfather taught me a variant of the
....snip...
Thumb Nail Test:

I have a new Boker Edelweiss razor .....snip... For this test, I stropped the razor as is my custom (linen and leather).
I then performed the Thumb Nail Test three (3) times.
....snip....
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?

This is a lot like a newbe stropping a "shave ready" razor.
The risk is larger than the gain so it is discouraged.

Any test that needs to be learned needs to be in the list
of things to discourage for beginners --- in experienced hands sure
it is a tool like any other that a craftsman may have.

For those that know how to hone a razor correctly
and recover from a lightly or badly rolled edge
sure give it a whirl. A reliable test should do no
harm with a minimum of training....

For me the most important place for thumb nail test is
at 1k bevel setting (also the thumb pad test). I do hate
the feel that a sharp edge gives me on my thumb nail
so I use the thumb pad test.

There are many tricks for testing the length
of an edge -- what works, works.

The problem with the TNT is that it may not harm the edge, but it certainly can't do it any good. It does, after 1K, show whether the bevel is set and that you have an "edge". But the TNT is somewhat like running the edge over glass (as is done with Feather DE blades to calm them down a bit) and in principle is similar to the breadknifing principle.

If done easily, it can confirm a bevel and its resulting edge. When I do it, I return to the 1K to make sure that the minimal dulling caused by it is eliminated. I haven't tried the HHT before and after the TNT, mostly because I don't worry about the HHT until I come off 12K, but it would show any difference. Even then, however, the test may backfire. A blade, after 1K, may pass the HHT because it retains a slightly sawtoothed edge. The TNT may serve to calm that down, and if done lightly, the HHT might fail. Sometimes a test can produce a result for differing reasons.

Originally Posted by ace

The problem with the TNT is that it may not harm the edge, but it certainly can't do it any good. It does, after 1K, show whether the bevel is set and that you have an "edge". But the TNT is somewhat like running the edge over glass (as is done with Feather DE blades to calm them down a bit) and in principle is similar to the breadknifing principle.

If done easily, it can confirm a bevel and its resulting edge. When I do it, I return to the 1K to make sure that the minimal dulling caused by it is eliminated. I haven't tried the HHT before and after the TNT, mostly because I don't worry about the HHT until I come off 12K, but it would show any difference. Even then, however, the test may backfire. A blade, after 1K, may pass the HHT because it retains a slightly sawtoothed edge. The TNT may serve to calm that down, and if done lightly, the HHT might fail. Sometimes a test can produce a result for differing reasons.

The bit about feather blades caught my eye.
Glass -- hmmm....
Yet some do "cork" a harsh edge....
i.e. run it lightly on cork so it shaves
like day two or three.

Feather blades... love em or hate them
they are sharp.