Thread: Explaining the thumb test

I've read a lot about the thumb test, not to be confused with the thumbNAIL test. But I can't figure out exactly how the edge is supposed to contact your thumb.

Do you brush your thumb along the blade, away from the spine and out and off the edge? (You'd be brushing the bevel, starting on the spine side and moving out over the edge.)

Do you somehow touch the actual edge with the pad of your thumb?

How do you hold the razor during all this?

Photos would be very helpful. I'm hoping to learn this as a supplement to the hanging hair test, which I think I understand, even though I can't get my razor to pass yet...

Joshearl, I think you pass your thumb pad across the edge (in several places) while holding spine down the edge up. Someone please correct me if I'm wrong.

I have questions about the thumbNail test(s) myself, but I'll wait 'til your questions are more thoroughly answered before asking.

Jordan

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.

I don't depend on this particular test much. What I do is angle the blade so the light is reflecting off the bevel, then increase the angle so that it's just stopped reflecting, then strop it with my thumb watch what happens to the reflection on the fin. If you've got a clean bevel and the angles right and you have a good light source you can see the hairline reflection of the fin as it turns, and can tell from the angle where the fin reflects versus the angle where the bevel reflects whether (and where) the fin is forming and if it has turned into a wire edge. You need a good approximation of a point light source to do this. Fluroescent doesn't work at all; a clear incandescent bulb works if it's a 4-5 feet away from the razor; and the sun works great. I use clear incandescent.

Check this document by Joe Lerch in User Gallery: http://straightrazorpalace.com/image...H/thumbtst.pdf It explains everything about thumb and thumb nail test.

Originally Posted by Kees

Check this document by Joe Lerch in User Gallery: http://straightrazorpalace.com/image...H/thumbtst.pdf It explains everything about thumb and thumb nail test.

Kees, I have looked at this before, and yes, perhaps I'm a bit thick, but I still don't understand about tilting the thumb down.

Is this to see if the blade slides as if to fall off your thumb nail? I don't see how this could happen if you're holding the razor.

Thanks

Jordan

Jordan,

Tilting your thumb down while holding the blade on it tests for some level of sharpness, I think. Dragging the blade across the back of the nail tests the evenness of the edge.

I think the motion being described in Joe's document goes like this: Stick your thumb out and hold it horizontally with the nail on the top. Bend your wrist so your thumb points at a 45-degree angle toward the floor. That's the angle you want.

I find that if I hold the razor's scales very, very lightly, almost cupping them in a half-open hand, I can more easily detect the subtle changes in feel while dragging the edge over the nail. Grip tightly and you can make a duller razor dig in a little.

The same goes for tilting your thumb. Use your hand on the scales to support the razor rather than gripping it. That will give it freedom to slip and start to fall, without danger of actually dropping it.

Someone please correct me if I'm off base here.

Thanks,
Josh

[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.[QUOTE]

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

I think that's right.

The traditional thumb test to evaluate shave readiness is as follows:

Hold razor fully opened by the handle with point "pointing" towards the ceiling. Lightly place moistened thumb at heel of razor edge, first 2 fingers on spine, and lightly move the thumb, not the razor, move the thumb lightly along the edge towards the point. The thumb should "stick" or bind along the edge. This is because the razor is actually slightly cutting into the outter layer of your skin. When the skin binds, stop, lift thumb and replace higher up the edge and repeat until you cover the entire edge of the razor. If the thumb glides smoothly along the edge without a "sticky" feel, the edge is not cutting into the skin and is not yet sharp enough to shave.

I can't emphasize enough that this test is done with a light touch, or you may do more cutting than intended. The fingers on the spine help control pressure and movement of the thumb.

Scott

Beats me the "right" way to do it. I lightly brush my thumb across the edge like you described, you can feel it catching if the blade is sharp because it wants to sink in. Running it along the blade sounds like a really good way to cut yourself.

I'm not an expert at honing, though, so hopefully lynn or somebody with real experience can chime in on this one.