Thread: Thumbpad test (TPT) questions

Hey, all. I've been thumbing my Israeli Personna DE blades to get an idea of what to expect from a sharp straight razor, and I am confused as to what I should be feeling for. I have read several descriptions of the TPT (for other newbies, it's when you moisten the pad of your thumb and lightly touch it to the edge of your razor), and I even have the relevant sections of the barber's manual posted here last week printed out, but I am not feeling the "drag" described in either the posts or the manual. Here's what I am doing:

1) Unwrap brand new IP blade from paper
2) Moisten thumbpad with water
3) Lightly touch pad to edge of blade, and slide pad along the edge very slightly to see if it "sticks", or if it feels gritty on a used blade.

The problem is, my thumb just kind of slides on the edge of the blade without dragging at all. Even when I apply enough pressure to dent the skin of my thumb and slide it. If I didn't know better, I would say I had a very dull edge, but these are brand new blades out of the package (and they shave fine as well).

I'm afraid to put even more pressure on the blade because I'm leery of getting a nice slice in my thumb, but I'm not sure what else to do. And I work with computers all day so it's not like I have callused lumberjack hands...

Any help on perfecting my TPT technique would be appreciated. I have read, and fully believe that edge evaluation is an important part of both stropping and (eventually, for me) honing, and I want to make sure I am doing it right.

I believe I recognize your problem.
The skin on my thumb is rather rough, so unless I soak my thumb in warm water for 15 minutes or so, the TPT tells me nothing, if performed that way. Using the tip of other fingers allows for better gauging in my case. My first successes were with using the very tip of the thumb, right below the fingernail, but lately I use the tip of my ring finger to perform the TPT (TRT, actually)

Hope this helps a bit,

Bart.

From my (currently invisible) blog:


TPT - Thumb Pad Test
Performing The Test:
1. Hold the razor in your dominant hand and aim the edge upward.
2. Place the fingers of your off hand along the downward facing spine for absolute control over how your thumb contacts the shaving edge.
3. With a moistened thumb pad, draw your thumb very gingerly across, not along, the edge repeating all along its length to feel how it grips or bites into your thumb print.

Interpretations:
1. If the edge has a faint tickling sensation and just starts to grip onto your thumb pad then you are in the right neighbourhood for a shave test.
2. If the edge bites and grips your thumb pad relentlessly wanting to cut in and not let go, then the edge may be overhoned.
3. If the edge tickles your thumb and feels like a very sharp knife with a good cutting edge then you are not sharp enough. This sensation is usually felt coming off a medium hone like a 4,000 grit waterstone.

Finer points:
1. The cross edge action of the thumb is done much more carefully than one would normally do it for a knife since you are looking for different responding factors.
2. I regularly perform this test after every few laps on the hone to chart the progress in the creation of the edge.
3. The sensations described above are from my personal vantage point and your perceptions may vary. The definitions cannot substitute for the actual experience of sensation since perceptions depend primarily on the tactile sensitivity of the tester. Calloused hands, for example, may find it difficult to accurately grade a razor's edge with this test.

X

ACROSS??? Thumb...across...the blade?

Ut-oh.........


Scott

Drawing my thumb across the blade has never told me anything when I do that. Well, eh, actually some "pling" and others don't. But apart from that, I really need to make small motions along the blade with my finger tip barely touching. It's the only way I asses the cutting qualities of an edge.
I think this might be one of those 'Your mileage may vary" things.

If a blade is truly razor sharp, with the way I perform the test, it feels like if it's covered with caramel, or some other sticky substance. It sort of sucks itself into the skin, and because of that, a little resistance can be felt upon pushing your finger tip forward along the edge. This sensation shows some variances in relation with the degree of sharpness. Only experience can learn you to read the finer nuances of that kind of blade gauging. I often compare between the blade in question and another blade of known sharpness.

That's the way I do this and it works for me.
I'm sure Xman's method works for others as well.

Best regards,

Bart.

I like that "caramel" description a lot, Bart, thanks for that. I think it's a sensitivity thing...I am just not attuned enough into what I should be feeling at this point. I will try with my fingertips instead of my thumbpad as you suggested, and try to feel the stickiness you describe. Since this are new, unopened double-edge blades I'm sure the stickiness is there, I'm just too clumsy to pick up on it right now.

Many thanks for the replies, all!

Originally Posted by Bart

Drawing my thumb across the blade has never told me anything when I do that. Well, eh, actually some "pling" and others don't. But apart from that, I really need to make small motions along the blade with my finger tip barely touching. It's the only way I asses the cutting qualities of an edge.
I think this might be one of those 'Your mileage may vary" things.

If a blade is truly razor sharp, with the way I perform the test, it feels like if it's covered with caramel, or some other sticky substance. It sort of sucks itself into the skin, and because of that, a little resistance can be felt upon pushing your finger tip forward along the edge. This sensation shows some variances in relation with the degree of sharpness. Only experience can learn you to read the finer nuances of that kind of blade gauging. I often compare between the blade in question and another blade of known sharpness.

That's the way I do this and it works for me.
I'm sure Xman's method works for others as well.

Best regards,

Bart.

The Thumb-Along-the Blade method is the one taught in the classic barber manuals. The Thumb-Across, I believe, comes from what you get when two different, but related, disciplines (knives and straight razors) mix.

While strumming your thumb across the blade probably does provide some type of sensory information, it's probably not THE specific information that best evaluates the keeness of a just stropped edge of a straight razor which is the whole reason for the TPT.


Scott

I will often use my thumb to test one way and then my fingers to test the other way. For me this was something that took a lot of time to develop the feel for what I was looking for. Sometimes I just need to touch the edge and not move across the edge. I often do this test before I strop to determine if I use the diamond pasted side first or not.

Originally Posted by honedright

ACROSS??? Thumb...across...the blade?

Ut-oh.........


Scott

The motion I teached from my grandfather (he was a barber from 1918) for TPT is a diagonal motion mostly across and little along like SWW-NNE.
I dont moist my thumb and I use a very very light touch, almost no touch!

Originally Posted by Yannis

The motion I teached from my grandfather (he was a barber from 1918) for TPT is a diagonal motion mostly across and little along like SWW-NNE.
I dont moist my thumb and I use a very very light touch, almost no touch!

Yes, I've seen barbers do this as well. Probably a variation of the classic method which I've also seen barbers do.

But the same barber who showed me the diagonal variant agreed absolutely not across the edge with the thumb - "that's for knives" he said, "not straight razors."


Scott