Thread: Testing an edge

thumb pad test

I remember when I was a kid watching my mother test a hot iron with a wet finger. She'd put her finger in her mouth to wet, then lightly touched the iron. If the iron was hot enough, the heat would immediately boil the saliva on her finger creating a vapor barrier and preventing a burn. This let her know the iron was ready (you can feel the bubbling).

Seemed crazy to me until I tried it. You're expecting a burn but it works like a charm.

The TPT is similar in that your brain tells you that you shouldn't do it. But once learned correctly, is a very useful and accurate indicator of shave readiness.

Scott

P.S. - In regards to comments as in a previous post stating that the TPT tests general sharpness, but not how sharp a razor is, here is a quote from a standard barbering text describing the TPT:

"A dull edge produces no drawing feeling. A razor that has the proper cutting edge produces a keen drawing feeling.
If the razor edge produces a rough, disagreeable feeling upon testing, it indicates that the cutting edge is still wiry."

This should give you a clue that there is some finesse and skill involved. As a newbie, be careful not to disregard the full value of these few, but important, edge tests (TPT and TNT) before taking the time to really learn them.

Don't run a shave ready razor accross your wet thumbnail as it will damage an edge, this test should only be used to assess the bevel sharpness at or below 4K. With the thumbpad test you don't just press and run your thumb along the entire edge of your razor or else you will be going in for stiches (assuming your razor is sharp). It is more like lightly brushing your thumb along a very small portion of the edge to feel for stickyness then lifting your thumb up before it cuts too far into your skin. Then do the next section of the blade and so on. Brushing your thumb accross the edge works OK with knives as you say, but in my experience it just does not give very good feedback with a straight razor. A razor that is sort of sharp but not near shave ready will feel almost the same as a shave ready razor. The real test of the quality of a straight razor's edge is the shave test, but it takes experience to learn what a properly honed straight razor feels like to shave with.

I'd recommend this very useful guide to edge testing. I use the TPT and TNT all the time. I'd be lost without them.

Originally Posted by Sticky

I'd recommend this very useful guide to edge testing. I use the TPT and TNT all the time. I'd be lost without them.

+1 on that.
I use the very tip of my thumb, right below the nail, to probe for sharpness with little slicing motions. It took me awhile to get the hang of it, but I now consider it a cornerstone of my ability to hone a razor.

Now why is this superb guide not in the library of SRP, or presented as a sticky in the honing section. I keep asking that, but no one ever answers.
Was it banned, because we fear that once we issue such a clear and thorough guide about honing technique, we won't have anything left to talk about here?

I use the thumbnail test when setting a bevel but stop at my 1200DMT. From that point on I use feel, not my thumb feel but the feel of the blade on the stone. A keen eye or magnifying glass also helps to look at the edge, but I mostly go by how the blade feels gliding on the stone. It should glide effortlessly across the stone with no rough feedback or hanging sensation on the stone. Once I get through the 8K stone I strop and then glide the blade over my arm, not touching the skin, swiping the blade through the raised hair. It should pop the hair to half height. If it does not, then I go back to the 4/8K Norton. If it tugs or makes a raspy sound like someone dragging sandpaper on steel but does cut hair, I go back to the 8K for another 10 passes then another 50 on the strop and test again.

The best test is to shave with it. Your face is very sensitive and you will feel dull spots or pulling from a not quite ready blade. Or you will look like you stuck your face in a food processor.

Originally Posted by Bart

Now why is this superb guide not in the library of SRP, or presented as a sticky in the honing section. I keep asking that, but no one ever answers.
Was it banned, because we fear that once we issue such a clear and thorough guide about honing technique, we won't have anything left to talk about here?

It's a conspiracy, if we told you then we would have to kill you. Seriously though, it is not the pyramid method (which is what is discussed and recommended here extensively) and as such Lynn does not advocate my honing methods. Many experienced members have also stated that they do not use sharpness tests, they just hone the razor and test-shave it. We have a relatively significant difference of opinion in the fundamentals that newbies should be taught and people should use to hone razors, and he runs the show here. I do plan on making and posting some in-depth honing videos in the near future of what I consider to be the fundamentals of honing a straight razor and my methods, but they might not be posted on this forum because of the above mentioned facts.

Another thought....

When sharpening kitchen or pocket knives, I often use a piece of newspaper to test.

I start at the top and try to slice all the way through the page, depending how sharp the blade is, the further the cut in the paper will be. Also this allows me to see which parts of the blade are dull and which are sharp, depending on which sections of the cut are torn/how clean the cut is.

With a razor being more delicate that say a pocket knife, will this undo all my hard work putting a nice edge on the razor? I suspect it will but thought I would throw it out all the same.

Cheers for all your replies fellas.


David