Thread: Edge Testing

I was wondering if anybody here has heard of the following test of sharpness for blades. I use it often for knife sharpening and learned it from the Murray Carter video. Murray is a knife maker and sharpener extraordinaire. In his video he decribes a method for testing an edge whereby you press three fingers held closely together against the edge with your thumb on the spine. You then proceed to move your fingers slightly along the edge. That's right, I said along the edge. The three fingers gives a large surface area and instant feedback to your brain. Anything but a perfectly sharp instrument will glide uselessly along your fingers with no tension or breakage. A sharp knife will give a tiny tug when you start to pull and your brain will know that any further movement will cut you. It's an excellent way to feel that toothy edge. The thought of this usually makes people queazy if they are not familiar with it. I think I might try it out on razors.

This test is discussed in depth on his DVD and I am in no way giving the complete instructions here. I would highly recommend you seek the complete text or view the film prior to using this method unless you are completely comfortable with the idea.

Larry,
Umm, DON"T <g>. I inadvertantly tried that. Before I sharpen a new, out of the box razor I test it against the inside of my finger or the pad of my finger. It will either feel sharp or not and from there I decide where to start. If really sharp it sticks, of dull, nothing. I often find I can actually press my finger hard againts the dull blade. I did this one evening with a razor that felt like a butter knife, dead dull, when releasing it from my finger I accidentally pulled my finger along the very dull blade just a tiny bit and it immediaetly sunk right in. Even a dull razor is far sharper than a knife.
Tony

Korndog,

I wouldn't do that with your fingers. That just sounds like a big cut to me.

Well, there is definitley a technique involved here. As scary as it sounds, if it is done properly, your brain will save you from being cut. I have done this test 100's (knives) of times with no cuts.

I use a modified version if Murray's technique, same principle just different body parts
I place the edge length wise on the side of my index finger so that about 1.5"-2" of my finger is in contact with the cutting edge, with the thumb on the spine. It produces a better "feel" for me than using the finger pads.

having said that, I would NOT do that with my razors. A "dull" razor will shame the sharpest of knives. So it won't give you much of an idea as to where the blade is in the "razor version" of shaprness. Your more likely to fillet your finger and still not have a comfortable shave

I get lots of feedback from the regular thumb test. WhenI nick myself, sometimes I can't feel it happen at all so I would expect the edge to cut in well before it gives enough feedback to tell. Lynn even talked about an Egyptian TI tht cut through a cloth and into his hand once before he felt it.

If you do try it, let us know how many fingers you loose (kidding, here's hoping for your safety)

X

Can you say "Reconstructive Surgery"?

Louis

I have heard of a test like this using only one finger. I don't doubt with practice it'll work. I would think by now you'd feel like I do though. That you just instinctively know when the blade is sharp.

Originally Posted by AFDavis11

I have heard of a test like this using only one finger. I don't doubt with practice it'll work. I would think by now you'd feel like I do though. That you just instinctively know when the blade is sharp.

Yeah, I guess you are right. There are many feedback alternatives to this test. Just a thought.

I'm stickin' with the shave test, but really enjoy seeing all the other tests that are out there. Thanks Larry. Lynn