Thread: Explaining the thumb test

This is one method. You can also modify the angle from 90 to 45.

As has been mentioned you can also run your thumb "along" the length of the edge, very lightly. I use both the 45 degree and along the edge.


[quote=joshearl][quote=mparker762]I think the traditional thumb test is lightly dragging your thumb at right angles to the blade (not parallel or you'll get cut). A sharp edge will kind of catch as your thumb goes across it.

So if I'm reading this right, I should do the following:

1. Lay the razor on its spine, edge pointing up.

2. Wet my thumb.

3. Drag the pad of my thumb across the edge at a 90-degree angle to the edge and a 90-degree angle to the blade. Like this cutaway view:

-----------------> (motion of thumb)
| (edge)
|
||
||| (spine)


Sorry for the bad ASCI art. It's my first attempt.

Thanks,
Josh

Originally Posted by Joe Lerch

The rule I've seen is not to use it after honing, but otherwise before stropping.

I meant right after honing...not stropping...duh...sorry

Originally Posted by randydance062449

you can also run your thumb "along" the length of the edge, very lightly.

OK Randy, I haven't gotten an answer on this. When you move along the edge, what do you feel? How could the edge drag anything in its sharp direction?

On the basis of this thread, I've been playing with a fresh single edge razor blade. I feel absolutlety nothing if I just touch it head on, and if I move gently along the edge, it feels perfectly smooth (I'm concerned about applying pressure). Please tell us exactly what you experience.

I've been told that the barber manual supposedly teaches this method. Not by a long shot. If it says anything it says touch down on the edge, and then it's supposed to stick or you're supposed to feel a "draw." What is that? When I put my thumb straight down on the edge, nothing sticks, ever, it just touches the edge and comes away.

The only time I feel anything is when there's a sideways component of the movement of the thumb. Then, a dull razor just slides across, and a keen one grabs it and moves with it.

I haven't heard anyone else say anything like this, but since I was a kid I had seen an old time barber do this test many times. Of course, I couldn't see any thumb movement. But when I was close enough (my eyes were a lot better then) I did see the blade jump sideways.

If you don't have an answer (or anyone else), I might just try to contact that master barber that did the CD. My barber has been deaad a long time.

Here is a description of the "thumb test" from another source, "The Barber Manual" by A.B. Moler, Copyright 1911, p.40:

"You test the edge of your razor after stropping by drawing it over the flesh or ball of your finger. Draw the razor carefully over the surface, or you may draw your finger over the edge, to detect its condition."

"If in perfect shape, it will have a smooth, keen cut that will not permit you to draw very far without cutting through, but if it is rough it will have a rather disagreeable feeling, although it may cut into the flesh just as quickly as the keen edge."

From this description of the "thumb test" it seems clear to me that it is the purpose of the test to slightly cut into the thumb, finger, etc. At least that is how it was originally taught in barber texts.

Although the above doesn't specify "drawing" parallel or perpendicular to the blade, It seems reasonable to me to conclude that moving the blade perpendicular to your flesh would not "cut through" nor result in a "keen cut" as mentioned above.

If a perpendicular move could "cut through", the same would happen during shaving when moving the blade perpendicular to the flesh of the face. But of course this doesn't happen.

At worse, a perpendicular movement of the blade could cause a severe abrasion, or even slicing off a flap of skin. But that would require so much pressure, it would certainly have to be intentional.

Cutting through, or keen cuts, occur when the blade is drawn parallel to the cutting edge.

Scott

Joe,

I just opened up a used disposable razor and tried the "test". There is a smooth feeling, but also the sensation of the blade cutting in. That is what the test is testing for, a smooth "cutting in" sensation, or "sticky" feeling. You do need to apply a little pressure, but not much, just the weight of your thumb or finger is enough. You should also slightly moisten the skin first.

Do you have thick or callused skin over your fingers? It takes a very sensitive touch to detect.

Scott

Originally Posted by honedright

"If in perfect shape, it will have a smooth, keen cut that will not permit you to draw very far without cutting through, but if it is rough it will have a rather disagreeable feeling, although it may cut into the flesh just as quickly as the keen edge."

OK. So, now you'r saying that it's a smooth feel that tells you the edge is sharp. This makes more sense.

It sounds like the idea is to feel any existing unevenness in the edge. But my experience is that the way I do the test I can get much sharper than jus a smooth edge. For example, when I first started learning to use the test I used a microscope as well. I gave up the idea because even if the edge looked perfectly straight at 100x, I still didn't get the cue I needed from the thumb test. That is, there was still a lot more improvement to be had. So, looking in the microscope before I passed the test and after showed no difference in edge continuity or smoothnes at 100x. At 100x, a 5 micron dip looks like half a millimeter, which you can easily see.

So, for this test to give the same results, your touch would have to sense less than a 5 micron variation (finer than the scratch line on the 4K hone) . Pretty amazing!

I'm starting to think that maybe there were two thumb tests, with the crosswise test coming later. After all, the test for sharpness is now grabbing the thumb not a smooth feel. This is supported by what I saw my barber do.

I think I'm going to locate the barber that did that shaving video and see if he knows anything about this.

Joe,

It is a smooth, and, cutting sensation. The "sticky" sensation mentioned is from the edge starting to cut into the flesh. You might also detect a "rough", cutting in sensation on an edge that is not propperly stropped. I think I touched on this in one of my previous posts where I mentioned the "quality" of the cutting sensation.

As mentioned, this test requires an experienced feel to get any meaningful information from it.

First ,though, you have to get past the fear of being cut. If done carefully, you won't cut yourself beyond the superficial "cutting in" descibed in the test. In fact, if you've ever nicked yourself shaving, you've already cut yourself much worse and survived.

Scott

Originally Posted by honedright

I just opened up a used disposable razor and tried the "test". There is a smooth feeling, but also the sensation of the blade cutting in. That is what the test is testing for, a smooth "cutting in" sensation, or "sticky" feeling. You do need to apply a little pressure, but not much, just the weight of your thumb or finger is enough. You should also slightly moisten the skin first.

I just tried a fresh single edged razor, and I noticed it's very difficult to touch it head on. Every touch produced a slight sideways motion and grabbing or drawing of the thumb. I never noticed this with a str8 blade because of it's size and weight. Could that be what the later manual is talking about? A soft downrard touch without intentional sideways movement nevertheless catches the edge sideways and you feel a pull or drawing on the thumb. It could even be described as stickiness because it resists pulling the thumb away.

If I place the thumb on the edge, I can drawi it lightly and it feels perfectly smooth, not sticky in any way. Also, I don't feel the thinness of the edge like I do with sideways movement.

You know, this smooth cutting is starting to sound like the feeling of the thumbnail test. And then the roughness is like what you feel with a wire edge or a coarse edge. My understanding was always that the thumb test is the opposite: smooth is bad and pulling is good.

Joe,

How about this: Take a sharp razor and deliberately slice into a piece of wet rubber. Make a linear slice with light and even pressure. Just use your thumb and finger tips to lightly hold the razor and pull it across, or draw it across, the rubber. Do you notice any resistance? Is it a smooth sensation? Does the rubber tend to bind the blade as it travels preventing going deeper without applying more pressure?

This is the same type of feeling you are looking for on your thumb, but in a much, much more subtle way. The moistened skin tends to act like the rubber.

Scott

P.S. - I just tried this on my dogs rubber "Kong" chew toy with a Henkles straight. Actually works fairly well to demonstrate roughly what you should feel doing the thumb test.

Look at this:

“Tell us about Sharpness of Razor blades?

If you carefully rub your thumb over the edge perpendicular to the edge, you should hear a high-frequent tingling sound and it should feel a little sticky.”

http://www.venusworldwide.com/razors.htm.