Thomas Trilby's Circus act at Prospect Farm was the best thing I've seen in years. So skilful and also so funny. He made huge soap bubbles using string on poles.
I know that bubbles produce colours by thin film interference. Some light bounces off the outside. Some continues through the bubble's liquid shell. When it hits the end of the liquid layer, more bounces back and the rest carries on through the bubble. White light is made of colours - light of different wavelengths that mix. If the precise distance the light has gone from the front of the thin film of bubble mix through to the inner edge of the bubble mix, if that is precisely a multiple of the wavelength of a particular colour, then that's the colour you see. Red has the longest wavelength and at the bottom of the bubble, the liquid is most curved. So from my viewpoint the light will have travelled furthest. This explains the grading of the colours.
