Thread: Light reflection and fineness of stone

I noticed recently that if I held my best (finest) finishers up to a light source, along the longest axis and tilted just a degree or two from the parallel line of sight, that there was a correlation between the sharpness of the image and the finishing quality given by that stone.

For example, I have have six cotis, some better finishers than others. The best finishers reflect the light source almost as a mirror would. The better cutters, or pre-finishers, give a cloudier reflection. The differences are subtle, about on a par with various HHT outcomes, and I suspect each individual would have to establish his own standards.

I've also tried this with my manmade stones. The 8K Norton gives a pretty accurate reflection -- though not as precise as my Eschers, Nakayamas, or even my Guangxi. The 4K stone shows a light source, but a very muddled one.

Could some of you try this and report back? It might be useful as a quick indicator of the finishing qualities of an unknown stone. I realize nothing will ever substitute for the actual honing experience, just as nothing will ever substitute for the shave test on a blade.

Or maybe it's just my fevered imagination.

What an odd sensation. First I took a couple of Eschers and then a coticule. I tilted them to the light and when I hit a certain plane the dry surface suddenly appeared to reflect as if it were uniformly wet. Very interesting and I never would have thought of it had you not brought it up. I don't know if it is useful beyond being interesting but it is that.

Haven't tried with a coticule, but I noticed this before with my C12k and Dragon's Tongue. I think the quality of the reflection has more to do with the way the stone's surface has been finished, though. To see what I mean, lap a hone with 400 grit wet/dry, then lap just half of it with 2000 grit. There will be a huge difference in the reflections you get from each half.

Not sure what bearing that may have on a stone's performance, but I seemed to get better results from the aforementioned two hones after lapping through 2000 grit (the DT, in particular).

I've been looking at the light reflection that way for years. It's one of the things I do with every hone when I first examine it. I guess I hadn't realized it was not a common thing. It is, as has been pointed out, more an indication of the finish on the surface of the hone rather than in indicator of the fineness of the hone, but the two do correlate to some extent.

My stones behave exactly the same way, especially the cotis. i actually use The Reflection Test as a way to evaluate them. In my experince, the mirror-shine cotis finish very much better than the others. of course, its important to lap up to as high asnyou can to get the shine. i try and go dmt325-600 sandpaper-1200 sandpaper, and often times 2000.

the shine will also reveal surface anamolies that require lapping to remove. And most importantly: i love a shiney rock.

Originally Posted by Utopian

I've been looking at the light reflection that way for years. It's one of the things I do with every hone when I first examine it. I guess I hadn't realized it was not a common thing. It is, as has been pointed out, more an indication of the finish on the surface of the hone rather than in indicator of the fineness of the hone, but the two do correlate to some extent.

Same here. I'm VERY new to sharpening razors, but I'd been doing it for sharpening knives, hatchets and chisels for a long time. The more reflective a surface is, the smoother its plane is. The more sawtoothed a surface is, the rougher its plane, and theoretically its edge. It's all about uniformity rather than "sharpness" per se. Our objective in honing razors is to bring two equally smooth planes into intersection along a single line as finely and consistently as possible. That's why we polish, use fine grit hones, use pastes and strops, etc.

Originally Posted by MarkinLondon

[snip]...the shine will also reveal surface anamolies that require lapping to remove. And most importantly: i love a shiney rock.

And that's the reason why I would use the reflection test. Not as an evaluation of how sharp the blade may be, but to search for wire edges, nicks, scratches, etc. The more reflective a surface becomes, the better those anomalies contrast against it.



EDIT: Sorry, I realized well after the post that the original discussion was concerning the surfaces of the hones themselves rather than the surfaces that they impart to the razors. My mistake, gents. My remarks were concerning the conditions of the edges, so I'm sorry if this brings about any confusion.