What is it...?!

Here's a little challenge - can you work out what this is? (I thought it was rather pretty.)

I'll tell you that it has been cropped, and contrast, brightness & saturation have been enhanced. But otherwise it's as it came out of the camera.

I'll post the answer tomorrow :)

PS added 31 Dec: Thanks to everyone who had a go - and well done to those who said it was the bottom of a saucepan!

I'm not sure what caused the effect - presumably something we've cooked in it has left a very thin residual layer on the metal. I guess these are interference effects, like you get when oil floats on water, with a reflection from the surface of the layer interfering with the reflection from the pan itself. So I guess the layer must be similar in thickness to the wavelength of light (400-700nm). The pan has already been carefully washed - it'll be interesting to see what happens when something else is cooked in it.

PPS Just to make it clear, this is the interior of the pan.