how does machined metal get the rainbow effect?

Post Reply New Topic

Just wondering if anyone knows how machined or turned metal gets the rainbow sheen similar to that of a trout.

I was thinking that it might be cool if I could get that in my aluminum lightsaber when I finally get it.

It's from being heated, but I don't think aluminum will react the same way, as what you are thinking. But, there is this chemical for artificially toning coins, that does exactly what you are looking for, with a very cool rainbow of colors. I'm not sure if it works on aluminum, because I'm only familiar with it's use on silver coins, so you'll have to Google "artificial toning" and find out. Hope it works out for ya.

That 'Rainbow Sheen' that you're talking about only happens with Iron, steel and to a certain extent stainless steel when it is heated. What's causing the color change to happen is heat treatment and quick cooling when heating, grinding, or other anything else that will cause the ferrous metal to heat and cool in a very short span of time. when the metal changes color in that fasion, you are actually performing a very primitive form of case hardening of the metal, not unlike what you see on the cutting edge of handsaw blades, and to an extent the reciever block of some rifles and shotguns. --If the metal turns a greyish brown, you have actually annealed the metal, which is to say, removed any of the hardening treatment that it has recieved.

--As Jawbrodt has stated, this will not work with nonferrous metals like the aluminum that you want to make you lightsabre from.

It's clearly not heated. I can tell the difference between the heated rainbow effect and the kind seen in something like a CD. I believe I've seen this in VCR spools and such.

It is a defraction grid you are talking about, many fine lines that act like a prisim. I think it works on any metal, for the dies that make CDs have it and transfer it to the CD. I have seen it on watch parts, overlapping circles, like scales, so the right cutter and a dremal tool, you should be able to work a surface. A drill press may be easier to work with.

If you are still referring to 'turnings', as in your OP, the "rainbow" effect is caused by the heat of friction, from the cutting action of the mill or lathe. I've used both, and have seen this many times, usually caused by using a dull cutting tool, improper cutting angle, or when trying to cut an excessively hard material.

rainbows caused by heat are fixed. You look at it from any angle, the reds and purples and whatnot remain in the same place. This is more like the CD effect. Inventor has the right idea.

The surface, as a result of microscopic pits from machining, behaves as a diffraction grating:

http://en.wikipedia.org/wiki/Diffraction_grating

I just ask the question on Google how does machined aluminum get a rainbow affect and saw many wrong answers.
When you machine a high grade aluminum T6 6061 with a very sharp end mill and the right speed and feed with a coolant.The rainbow affect can be produced.Some have said like a cd,they are correct.

I love that rainbow effect.

The original poster left this site 13 years ago, and he asked his question 14 years ago. So be aware that he isnt likely to act on any advice you give him about metalworking.

But its an interesting subject of perennial interest.

"Color" is what we see when we see light only a narrow range of frequencies. When light passes through a prism short frequencies are bent more and long wavelengths less- so they get spread out by frequencies resulting in the rainbow of colors. Some reflecting surfaces have the same prism effect. Not sure how that works with surfaces though.