The cloud tank represented a fascinating pre-digital approach to atmospheric effects in cinema. This technique, used primarily from the 1970s through the 1990s, involved creating layered water tanks to generate organic cloud formations that looked more natural than hand-drawn animation. Close Encounters of the Third Kind (1977) featured a 7x7 foot tank that became a staple for visual effects artists seeking to create realistic sky phenomena.

The technical process required precision and patience. Artists filled tanks with salt water, added a plastic barrier, then topped with fresh water. After removing the divider, paint injected between the density layers created billowing cloud effects when filmed. The technique demanded substantial resources—9 tons of salt were used for Raiders of the Lost Ark alone—and offered limited control, requiring extensive shooting to capture usable footage.

Filmmakers across multiple genres utilized cloud tanks to create everything from alien atmospheres to supernatural weather. Industrial Light & Magic perfected the technique for films like Star Trek: The Wrath of Khan and Poltergeist, where physical ingenuity produced effects that digital tools would later replace. By the late 1990s, computer-generated imagery rendered these labor-intensive methods obsolete, though the ingenuity behind them remains impressive.