What Causes a Rainbow Pattern When Heating Metal?

[Fusilli_Jerry89]

I was just curious of something and was wondering if anyone could shed some light on this.

I have a metal screen (like the kind you have on your water taps). I think it is made out of steel or something? Anyways, I was bored one day so I put a lighter up to it till it started glowing red. After the glowing died down, I noticed a rainbow-like pattern perimeter around the previously-glowing-red circle. Almost like the pattern found in oil on the street.

Does anyone know what could be causing this? Could it just be something the metal is coded in that is being pushed to the outside or something?

 

[Borek]

Thin layer of oxides. Perceived color depends on the layer thickness. It is not much different from the colors seen when you put drop of gas or oil on water surface.

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