Thread: Thumb along or across blade?

After reading a number of sources about testing for the sharpness of a blade, there appears to be some confusion. Some sources say the pad of the thumb should be run gently "along the edge" of the blade. Other sources say the thumb should be run "across the blade." There's a big difference between the two. Will someone please clarify the proper way for testing a blade? Thank you.

Along. Can't really tell sharpness with across...

Wet your thumb pad and holding the blade in you opposite hand with the cutting edge up lightly place the center of your thumb pad against the cutting edge and move it up the edge. If it slides with no resistance the edge is dull. If it is 'sticky' with resistance it is getting sharp.

This is done lightly and with care. Not with so much pressure that you slice you thumb pad open. I try a spot and then lift by thumb and try up further working my way up the blade. I've seen someone describe it as bouncing and maybe it is kind of like that.

Randydance suggested to me to use a new DE blade to accustom myself to the feel of the TPT and that was very helpful for me.

I don't do it much with SRs, only off the 1k stone, but when sharpening knives, I run my thumb across the edge and slightly along, but at a ~45 degree angle so the edge catches the pad.

I use reflections off burrs and running my finger off the edge of the blade to feel the burrs when using higher grit stones.

I finally screwed up the guts to try it, and fortunately I had both a sharp and a dull razor to try it on. It really works. Just be gentle. You'll feel the sharp blade "stick," but you have to look really hard to see where it cut you -- very shallow. I couldn't see anything with the naked eye.

Originally Posted by ziggy925

I finally screwed up the guts to try it, and fortunately I had both a sharp and a dull razor to try it on. It really works. Just be gentle. You'll feel the sharp blade "stick," but you have to look really hard to see where it cut you -- very shallow. I couldn't see anything with the naked eye.

Like I said I started learning it with a DE blade to get the feel. I had been doing it on many blades for awhile when I heard it was supposed to cut a layer. I looked at my T pad and it wasn't cut. I figured it was because I work on bicycles a lot and have calluses on my finger tips. Then I took an eye loupe and looked and my T pad was like a plowed field with furrows.

I think if you have a really sharp one you will run your thumb along the edge only one time Jimmy is right.