Ice Crystal Formation on Frozen Soap Bubble

May 30, 2022


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Photographer:Patricia Rasmussen 

Summary Authors: Patricia Rasmussen; Jim Foster

There are several things of interest visible in this image of a frozen soap bubble, which is approximately 1 in (2.5 cm) in diameter. The soap bubble film is a sandwich made up of two soap layers with a water layer in between. Colors near the central portion of the bubble are likely due to diffraction processes -- light is interacting with the thin soap film. Light waves are diffracted or scattered by the varying thickness of the film in such a way that the waves interfere with each other, creating regions of enhanced color (constructive interference).

Frost crystals form in the water layer part of the bubble film; the bubble itself is a hollow sphere. When photographing the crystals, the depth of field is very shallow. So, the photographer chooses the place where crystal growth is most active and the crystal pattern most beautiful. Thus, the focus is either on the front or back wall of the bubble. In this case, the back wall is prominent, while the growing crystals on the front wall give a cloudy/hazy illusion to the image. Note that as the bubble ages, the film becomes thinner, and the color fades just before the bubble pops. 

This photo was taken from my unheated garage on February 24, 2022. The bubble is blown using a straw onto a base of snow, artificially backlit, with some purple-tinted cracked ice for interest. "Bubblers" say this is a highly addictive photographic subject because of the seemingly infinite variables that cause the coloration and crystal growth. It is! Click here to see a video of the crystals forming between the inner and outer surfaces of the bubble. Notice in this video that initially the crystals are rapidly swirling around the bubble, likely from my breath as I blow through the straw.

Photo details: Canon 90D camera; F11; 1/250; 100 mm focal length; ISO 800. Post processing was general—levels, contrast, and a small crop.


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