Soap films are ephemeral and ever-changing. The shifting concentration of surfactants along the surface of the film, combined with thermally-driven convection, keeps the fluid in motion. The shifting colors reflect subtle changes in the soap film’s thickness. Over time, gravity drains fluid from the top of the film, thinning it to the point that it appears black. This photo from Bruno Militelli captures all of that detail in a striking and fascinating image that earned him 2nd place in the Manmade category of the Close-Up Photographer of the Year awards. You can find more winners of the competition here, and more of Militelli’s work on his website and Instagram. (Image credit: B. Militelli)
“Delusion”
Jake
Thermal effects can appear, in particular if the soap film is drawn from a liquid bath — a higher evaporation rate at the top will lead to a gradient of temperature — but the main effect is buoyancy-induced convection: thin patches of soap film are lighter and rise due to gravitational effects.