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Cloud tank special effects

posted by Jason Kottke   Mar 25, 2015

To simulate unusual cloud formations in movies (like Close Encounters, Raiders of the Lost Ark, and Independence Day), special effects artists injected paint into tanks containing water with two different densities.

A cloud tank consists of a bottom layer of salt water and a top layer of fresh water and when various forms of liquid are injected into tank, clouds are produced. This was the common technique that Hollywood used for decades to capture supernatural weather.

The developer of the cloud tank effect, Scott Squires, wrote a post detailing how it was accomplished.

Next white liquid tempra paint is injected in the fresh water portion (top), usually just a few inches from the dividing line of the fresh and salt water. Think of a large syringe with an aquarium tube going into the water. When the tempra paint is injected it billows outward like cumulus clouds and will tend to sink a bit. But the salt water prevents it from going lower so the ‘cloud’ tends to flatten it’s base on the salt water line and and billow outward, similar to real clouds based on air pressure levels. Avoid going below into the saltwater since the clouds will just drop to the bottom of tank.

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