Water tank with controlled lighting, fog machine, color filters — creates atmospheric effects (clouds, fog, underwater). Shot separately, composited later.
A Cloud Tank is essentially a controlled water basin—typically between 1x2 and 3x4 meters in size—where atmospheric effects are created, which are then overlaid onto other footage in post-production. The setup functions like a small special effects stage: you fill the basin with water (or sometimes with colored water or special particles), hang lighting rigs in it—usually HMIs or LED rigs for precise control—and pump in fog. The fog mixture diffuses in the water, is lit from below or the side, and the camera is positioned in front, filming these cloud and fog formations. The footage is typically shot against a black background so it can be composited directly into VFX software later as a luminance key or alpha channel.
In practice, the Cloud Tank was long the standard tool for organic fog, cloud, and even underwater effects before volumetric CGI solutions became widely available. The advantage lies in its physical authenticity: light scattering, diffusion, turbulence—all of this occurs naturally and doesn't need to be simulated. You can experiment live, try different fog feed rates, adjust the lighting, and immediately see how the material behaves. This often saves time in editing.
The technical aspect requires patience: lighting and the fog machine must be synchronized—not too much fog, or you won't see anything; not too little, or it will appear thin. The cinematographer sets up on a stable tripod and typically shoots in 4K or higher, as Cloud Tank footage is often heavily enlarged and integrated into other scenes. The background must be absolutely black—black velvet, not just black paint. The water itself should also be undyed and distilled, as lime and impurities can cause light to appear patchy.
Today, many productions use Cloud Tanks for specific shots—dramatic explosion aftermaths, ghost effects, atmospheric underlays for scenes—where a computer-generated simulation might appear too sterile, or where quick creativity and iteration are needed. The editing suite then receives clean, high-quality footage that is immediately ready for use.