Unexplained optical effect in reflection off my VG-10 blade

U

Uncle Bill

Joined
Aug 24, 1999
Messages
434
There's an optical effect in the reflection off my VG-10 blade (Calypso Lightweight) that I can't explain.

The finish is factory - light, vertical grind or brush marks that are so fine I can't feel them when dragging my thumbnail across them from the tip back toward the handle: overall a very nice finish just this side of mirror.

Now here's the optical effect. When I hold the blade at just the right angle under a strong light, I see a ripple pattern that looks kind of like waves of water headed toward the beach (edge). And it looks almost as though these ripples are beneath the surface. I can't feel them at all.

Can anyone explain this effect? Does it have anything to do with heat treat? Is it a pseudo-damascus kind of not-quite-alloyed thing in this specific steel?

I'm all ears. BTW, this blade cuts like nobody's business. Whew! I'd call it a scalpel, but that would be an insult to its sharpness. Sal's got a winner with this little tool.
 
I've seen similar ripple effects on some ancient Japanese blades (15th century and later); unfortunately, these were under glass at the Montreal Museum of Art and they wouldn't let me fondle the blades. Dunno what caused it. Maybe my breath marks on the glass hampered the view.
 
I can't say for sure, but I could speculate why you might see light and dark banding at certain angles. I would guess that you are seeing light diffraction effects combined with curvature on the blade. (or your seeing something else entirely)

Pardon me if you went through all this in college. If you have very closely spaced and very uniformly spaced scratches in a shiny surface they can reflect light in a very non-uniform manner. Light may reflect back to your eye from multiple ridges in such a manner that there is an even multiple of wavelengths between the distance from the source to your eye via the multiple ridge-reflection-paths and cause you to see a bright band. Or you could have something in between where some of the light comes together at your eye in sync and some comes in out of sync (therefore you see less reflection or darkness).

Things like this depend a lot on the spacing of the scratches, the angle of observation, and the color of the light. If you are looking at a surface that is angled-away you might see light and dark banding (I'm not sure off the top of my head). I'm sure that you could at least see light and dark banding if you looked at a diffraction grating (pattern of scratches) on a slightly curved surface.

If you were seeing a diffraction effect it would also tend to seperate out colors of your incident light like a prism. So you might want to see if there was a secondary effect where you saw a little-bit of rainbow coloring in the reflected light or some different color to the reflection depending on the angle of observation.

All of this would be due to patterns in the fine surface scratches left by the polishing process. If you polish by using a rotating wheel it is pretty easy to leave a regular pattern of scratches. If you used a vibrating or orbital sander for your final polish you wouldn't see a diffraction pattern.

Play around with your reflection and try and make other observations. This is how scientists learned about the wave nature of light.

Good luck, Newton

 
Jeff, if you're talking about some sort of an optical moiré effect, I don't think that's it. it's too uneven to be related to the scratch lines, IMO.

 
How long have you been staring at it?
Have you taken time away from the new knife to eat? (Sleep?)

Maybe you should put it away in your pocket for a few minutes and take a break.

I found that usually helps when I start seeing things in my blades. (Or when they start talking to me)
 
The effect looks as though the surface is not smooth. It looks as if there are physical waves in the metal, sort of as though the bar had been compressed before grinding.

The strange thing, as I mentioned before, is that the surface is utterly smooth to the touch, right where it looks rippled.

Too bad the resolution on computers scans is so low. I'd love to show this to the forum.
 
Or perhaps what you are seeing is the steel's grain pattern.


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If a person with multiple personalities threatens suicide, is that considered a hostage situation?

 
Misque,

You've got a VG-10 lightweight calypso jr. too, don't you? Can you see this effect on yours?

(Clean off any grease, oil, soap, etc. Look at a clean blade.)
 
Yeah,
Now that I've found my glasses, I see what your looking at. I believe it has to do with the smelting process. when a steel is hot rolled out during the manufacturing stage it develops a "grain" that you can see when the steel has been polished. This is probably not the best comparison, but, I've seen this before and it looks to me almost like the grain you see in wood. It runs in lines or waves usually parallel with the blade.
I'm no expert on this and I may be wrong. I hope some of our resident steel gurus see this and elaborate further as now I'm curious too.
wink.gif


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If a person with multiple personalities threatens suicide, is that considered a hostage situation?

 
If your effect sounds more like Misque describes, he's probably right and you're seeing rolling effects.

What I was describing is not a moiré effect. A moiré effect is the interaction of two patterns that seem more intense where they are coincident and may cause the eye/brain to detect sort of a third pattern. Diffraction effects are literally the interference of in and out of phase light waves that are forced to take similar, but unequal paths. Moiré patterns generally don't cause color effects, while diffraction effects are always wavelength (aka color) dependent. That is one of the reasons that I said to look for color effects to determine whether you had a diffraction effect or not.
 
At first I thought it was caused by regularly spaced scratches acting as a diffraction grating but then I came to this post:

"The effect looks as though the surface is not smooth. It looks as if
there are physical waves in the metal, sort of as though the bar had
been compressed before grinding.

The strange thing, as I mentioned before, is that the surface is
utterly smooth to the touch, right where it looks rippled."


Now I know what you're talking about. When you polish a blade you go through a series of steps, sanding finer and finer, and then go to your polishing buff. The buff works differently; it isn't just a finer version of the sanding process, removing metal by simple abrasion -- instead, although there is some simple abrasion taking place, most of the work is done by melt-abrasion -- the heat of friction softens an ultra-thin surface layer of the steel and it flows and fills in the scratches. If the scratches left from prepolish are sufficiently fine and you removed all traces of coarser stages before you got to the prepolish stage and you buff sufficiently long you can get an essentially perfect polish, to the naked eye anyway, but more usually it isn't perfect, especially in factory knives. Instead the steel flows over the scratches left by earlier grinding and makes them almost invisible, but there are still traces and if you look close you'll see ripples. The surface is smooth to the touch because your fingers are far too coarse an instrument to detect those tiny ripples, but your eyes can detect them when you look close. It's not the grain of the steel; it's the parallel grind marks after they've been smoothed over and obscured by buffing.

If you want to see what the grain of steel looks like try etching a piece -- it's totally different, dots rather than lines.

(The same melt-abrade effect occurs in polishing gemstones, btw, including diamond, which has a fantastically high melting point and can't be melted in air anyway because it'll burn first -- but you can melt a very thin surface layer with friction, and it's even possible to polish diamond on a cast-iron lap with no compound at all, even though cast iron has a much lower melting point than diamond -- the iron conducts heat away from that tiny surface layer so it never gets hot enough to melt; the surface of the diamond does melt -- only an atom or two deep, you understand; this is all happening on a microscopic level.)

That's a common sight when you look at blades closely; I bet if you look at all your knives in a good strong light, turning it to different angles, you'll find few if any of them are perfectly polished.

Get all your knives together and go look at them under the high-intensity light at your wife's sewing machine ... if she wonders if you've gone nuts, just explain that thousands of men all over the world are looking at knives under their wives' sewing lights; it's a worldwide phenomenon started by a post on the internet ... and a two-headed calf was born in Israel yesterday....

-Cougar Allen :{)
 
Hmm...interesting posts. I was noticing this effect on my Military just last night.

I got a scratch on the finish and was looking at the blade under a magnifying glass and bright light. The scratch appeared to be on the surface of the blade, while the faint lines of the finish seemed to be under the surface of the blade. They also seemed to be wavey and almost 3-D.

It sounds like your explanation is on the money, C.A. Or maybe I just took the brown acid by accident.

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Cerulean
Denver, CO


 
And all this time I thought it was me. Thank you all.

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Can it core a apple?
 
I've seen this also in alot of my Spydies. We might need to ask Sal.I seem to only find it in some of the Spydies produced in Japan.Not all from there exhibit this pattern,so it must be from one manufacturer.

lbwheat
 
Drat. I supposse I'll have to buy a Calypso just so I can see these cool waves. Some people have all the fun.

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Hoodoo

Doubt grows with knowledge.
--Goethe
 
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