Why does oil sometimes get weird colors in it. It will shine blue, purple, or yellow even. It kind of looks like the colors you get when you case harden metal.

Question

Why does oil sometimes get weird colors in it. It will shine blue, purple, or yellow even. It kind of looks like the colors you get when you case harden metal.

In: Chemistry

Answer 1

iirc, it’s due to the refraction pattern of the light hitting it. [Fatty acids](https://en.wikipedia.org/wiki/Fatty_acid#Types_of_fatty_acids) and oils generally are hydrocarbons (compounds made primarily of hydrogen and carbon). Unsaturated hydrocarbons will have at least one double bond in the structure, whereas a saturated hydrocarbon won’t have one because the carbon chain is saturated with hydrogen and no double bonds are present.

ANYWAY, double bonds in fatty acid chains tend to lower their melting point, for a couple of reasons, the main one being that, should the double bond be a cis double bond (cis meaning on the same side), it creates a bend in the chain, making it harder for the molecules to fit nicely together. Trans double bonds (trans meaning opposite sides in this case) don’t affect the angle of the bonds that much at all so they have higher melting points since the molecules are more closely packed together.

ANYWAY, double bonds and single bonds between molecules have different energy levels and, therefore, absorption and refraction patterns. It gets even more silly when double bonds are spaced in a way that causes [resonance](https://en.wikipedia.org/wiki/Resonance_(chemistry)) where the double bonds will become dynamic as opposed to static. Basically those electrons can alternate to different positions on the chemical, back and forth, functionally making a chemical with resonance, more of a mixture of the same chemical with varying electron positions… at the same time. This makes the light refraction patterns more diverse since certain resonance forms of a chemical may have vastly different positions of electron density and thus, different reactivity.

So… when light hits the surface of an oil spill, the chemistry of the oil is influx since, it’s in multiple different forms that are vacillating back and forth at light speed. The oil is able to absorb multiple different wavelengths and refract them in a [dispersed](https://en.wikipedia.org/wiki/Refraction#Dispersion) pattern that shows more than one wavelength..

I’m starting to think I’m not doing a good job of explaining this to a 5yo, so… uhhh….