Rubbing your thumb across the blade


March 4, 2013, 09:03 PM
Ok my father was an avid knife collector and he was quite anal about keeping them sharp. I remember he would take his thumb across the edge to test the sharpness. Unfortunately, he passed away before teaching me how to use sharpening stones.

What was he feeling when he used his thumb? I just purchased a benchmade knife and tried to compare my new knife with my dull kitchen knives. I didn't feel any difference. So what am I missing?

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Yo Mama
March 4, 2013, 09:16 PM
Maybe your kitchen knives are sharper than you believe? :)

I do this across the blade just as habit from others, but I'm not happy untill the blade can shave hair off my arm.

I also was never shown how to sharpen, I had to seek out and still learning how to best get that edge. I'd recommend a Sharpmaker from Spyderco for starters, and a good strop. The Sharpmaker comes with a nice DVD on how to sharpen everything you own with an edge.

March 4, 2013, 09:20 PM
If you're feeling for the wire edge some people consider it proper to use the pad of the finger, but you shouldn't "test the edge" with the pad of a finger (even though people do).

Use the edge on the nail of the finger to find out if it bites in or cuts a smooth line to test an edge.

March 4, 2013, 10:01 PM
But remember, whatever you do to test the edge is the first thing that starts dulling that edge.

March 4, 2013, 10:27 PM
"Sharpness" can be more than what meets the..'finger' It seems the sensation from tiny - microscopic burrs pulled up on the edge feel sharp, and they are. A sharpening 'steel' will cause those burrs to lift up on a nicely beveled blade. The type and hardness of the blade steel also has a lot to do with it. In my experience, a perfectly honed really hard (esp. a straight bevel, not hollow ground) steel may not feel as sharp as a milder steel edge that might look like a chain saw under a microscope, but will cut cleaner and last longer. I have a nice Damascus hunter that cuts like crazy, and I think it's due in part to the fact that all those layers of dissimilar metals creates that micro saw-tooth effect.

March 4, 2013, 11:57 PM
Interesting. Thank you for the replies. I'll try the fingernail test instead.

It also makes sense why the knives didn't feel any different.

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CA Raider
March 5, 2013, 09:54 AM
Have to say that I do exactly the same thing as your father.
I use the pad of my thumb or finger to check the blade edge when I am sharpening knives. I have never cut myself ... and I've been doing this my whole life. So it does work if you develop a sensitvity for what you are doing.

I use my skin to feel for a burr on the metal. I'm looking to see if the blade has been sharpened too many times on one side, and not enough on the other. I can also tell when the blade is very sharp and ready to go.

You can develop this touch. Just do it very lightly and try to feel the blade ... don't use a slicing action that cuts your skin.


March 5, 2013, 10:20 AM
Learning to sharpen a knife is a skill anyone can learn and I recommend it is a natural thing to do. Now as for running a thumb over the edge I have a different method similar to the one Murray Carter uses. He pretty much covers it all in these videos listed here Now if that doesn't work do a search on "Carter sharpening a knife".

March 5, 2013, 08:04 PM
I rub my thumb across the blade too (perpendicular to the length, not along the blade!)

I guesstimate the sharpness based on how easily the blade can fray off the outermost layer of skin; just very very thin little shavings.

However, I got a Spyderco Ladybug and tried this right out of the box, and the blade took off a hefty chunk with no resistance at all! Not enough to bleed but it was a bigger chunk than I intended! That knife was sharper out of the box than anything I've handled before.

March 5, 2013, 08:56 PM
Even though I use my finger...I probably shouldn't. I just use my fingernail to check. Using my finger, I can tell for inconsistencies in the edge.

March 5, 2013, 09:03 PM
Yes, finger nail is safer.

I alway used a stone, never figuring how the chef can whipsaw a blade into sharpness.

The tiny sawtooth sounds great. Sharks thrive on it.

March 5, 2013, 09:07 PM
I have used my thumb on the edge for a long time but when I started making knives I went to the thumb nail test - hold it at a 45 degree angle and see if the egde "catches" - it has to be pretty sharp to catch there. I also used to shave hair on my arm but quit that quickly as I was gonna be bald on my arms!

March 5, 2013, 09:16 PM
If you've ever tested a fishhook for sharpness, the same applies. Without any pressure run the edge down the thumb nail. If sharp, the blade will bite into the nail immediately. Of not, go to a very fine Arkansas stone and hone the blade. Sharpening stones come in different grits and you should own several. Practice with an inexpensive knife until you develop the touch. Really good feeling when you get the process down pat. Not everyone can sharpen a knife correctly. Us old timers learned as kids when it wasn't a crime for dads to give their sons a pocket knife.

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