The Science behind Soap Film Photography

Do you add colors? Is this digital? Are you using polarized light?

These are some of the common questions I get when people look at my iridescent abstract art. My answer always is, “No, the colors are completely natural. It’s just light breaking up into different colors like in a rainbow.”

I’m creating this short explanation for the curious souls who love science as much as art and cherish the intermingling of these seemingly disparate domains. Understanding the science behind the colors in soap bubbles can help us to appreciate their beauty even more.

A film of soap is very thin, measuring around 300-700 nanometers in thickness. Just for contrast, a human hair is about 80,000 nanometers thick. The physical phenomenon that causes the colors is aptly named Thin Film Interference. It is made possible by the delectable coincidence that the wavelength of visible light also falls in the 300-800 nm range.

Visible Light

Visible light is composed of different colors that correspond to different wavelengths within the electromagnetic spectrum. The colors of visible light are typically described as red, orange, yellow, green, blue, indigo, and violet (ROYGBIV).

Each of these colors has a different wavelength and frequency. Red light has the longest wavelength and the lowest frequency, while violet light has the shortest wavelength and the highest frequency. Our eyes can detect these different wavelengths and frequencies, and our brains interpret them as different colors.
When the light hits the film of soap, most of it passes through. Some of it bounces back from the top of the film and some of it reflects from the bottom of the film. When viewed from an appropriate angle, we begin to see various colors and patterns.

The light reflected from each surface comes together resulting in Constructive Interference and Destructive Interference.

Constructive Interference

Constructive Intereference Soap Film Photography
Constructive interference is a phenomenon that occurs when two waves meet and their amplitudes (or heights) add up to produce a larger wave. In other words, when the peaks of one wave coincide with the peaks of another wave, or when the troughs of one wave coincide with the troughs of another wave, the waves reinforce each other and create a stronger wave. In the image above, the two blue waves come together to create a stronger wave depicted in red color.

Roughly speaking, the wavelength of Red Light lies in the 620-750 nm range. When the thickness our film matches that, these waves combine and shine through. We see Red and Orange type colors in the thicker areas of the soap film. On the other hand, thinner areas in the 300-450 nm region tend to produce more Violet and Indigo shades.

The colors change as the thickness changes, often due to gravity which pulls the thicker material down.

Destructive Interference

Destructive Interference Soap Film Photography

Destructive Interference is the opposite effect. When two waves meet in such a way that the peak of one coincides with the trough of the other, they cancel each other out. In the image above, the blue and black waves are counterproductive resulting in a flat line or zero amplitude.

Have you used noise cancelling headphones? They make use of this phenomenon to eliminate noise. This is done by first measuring the ambient noise and then creating precise waves that will cancel these sounds by being out of phase.

With this in mind, take a look at my Artist's Statement on iridescent abstract photography. You might also enjoy revisiting the abstract collections.