Hand Tools Archive

Re: studying edge failure...somewhat obscure

David Weaver
It's rolled over, you can see by the shadow (as you're aware, i'm sure, the toplit metallurgical scopes are very sensitive to just what surface is reflecting right back, so edges that roll off can be hard to get a good image of), but very smooth and very fine.

The buffed edge rolls off into a little bit of darkness, but the very edge is still visible. Coincidentally, scuzz on the edge (jagged or wire edge bits) manages to show up easily because some part of it is reflective back to the lens.

All that said, instead of looking like a stoned edge, it looks more burnished like an oxide edge. I don't think this is burnishing, rather it's the inability of particles to cut very deeply just because their backing medium has no conviction.

The PC hooked to my metallurgical scope is near death, but I may be able to convince it to work this week to get a picture of this edge on a knife. my setup is a flat setup, so it's hard for me to get the picture of the bevel side on anything - the toplight comes down onto the bevel and is reflected into lateral space, never for whatever it's carrying to be seen again through any eyepiece of camera, so little knives and razors are easier to photograph - I just have to prop something under them so that the bevel is co planar to the lens.

At any rate, the oxides on a soft surface also leave a smudged looking edge because nothing is cutting deeply, or perhaps if it is, it's below the visible wavelength in size. We don't see edges like that in woodworking much because they disappear quickly in use. They've become popular in razor sharpening because you can be new and kind of a hack and use them easily, and when I sell a kamisori (because they're hard and will hold an edge like that for a little bit), I will sometimes leave the edges like that with minimal stropping to give people the shocking experience they want.

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