How 'cloud tanks' shaped Sci-Fi
- Alex Iwanoff
- 15 hours ago
- 4 min read
In space-related movies, there's a question every visual effects artist eventually faces: how do you create nebulas or wormholes nobody has ever seen up close? How do you film the infinite when you’re standing, well, on earth?
And somewhere in a dark room, across many decades of cinema, the answer was surprisingly simple: Water. In a tank. Mixed with various things.
CLOUDS IN A TANK
Like most great effects breakthroughs, it started with a vague idea, no money and a problem nobody knew how to solve.
During the production of Close Encounters of the Third Kind (1977), visual effects supervisor Douglas Trumbull needed a way to show massive alien ships emerging from dense, turbulent clouds. The reference? Cream swirling through coffee.
Scott Squires, who had just joined the production as an assistant effects artist, was handed a 20-gallon aquarium and twenty dollars to figure it out. By the end of the week, as he describes in his blog, he had developed what would become an iconic practical effect technique that would survive well into the digital era: the cloud tank.
“After brainstorming with Doug and some other people—and using my knowledge of photography, chemistry, physics, and some other things—by the end of the week I developed the cloud tank that was used in the movie”, Squires told to the Chicago Reader.
The setup itself was simple: salt water sat at the bottom of the tank, with fresh water layered above it. Because the two liquids have different densities, they resist mixing. White paint injected near the boundary line would spread horizontally and curl into formations that looked like atmospheric turbulence or massive cumulus clouds.
The technique proved so successful that it quickly made it into films like Raiders of the Lost Ark, Ghostbusters, Poltergeist and even Independence Day, where almost 20 years later, it was still being used.
And once artists realized these liquid reactions could mimic natural turbulence, the technique evolved far beyond clouds.
NEBULAS AND INTERNAL MATTER
For Star Trek II: The Wrath of Khan (1982), the effects team at ILM had to create the Mutara Nebula: a glowing storm of gas. To do so they went back to the tank, but pushed the chemistry further. Instead of paint, they injected white latex rubber before introducing ammonia into the mixture. The reaction caused the latex to curl and twist into dense, organic and abstract shapes that were constantly shifting.
“Getting the “look” of this alien environment was very important, and much time went into experimenting with various approaches, materials, unusual compounds, any and everything to achieve what we wanted”, DoP Ken Ralston in American Cinematographer.
Colour was relatively simple to add. Because the base material was white, the formations could essentially be painted with light and gels. The real challenge, however, was time. As soon as the structures emerged, they immediately began to deform, disperse and ultimately vanish. The team had only a few seconds to light and capture the formations before they collapsed into a murk. As Ralston explains:
"It was difficult maintaining any sort of continuity with this abstract system, and we had to shoot a lot of film to give us enough material so I could give the nebula sequence a cohesive look from shot to shot"
But the cloud tank didn’t stay confined to portals and outer space.
In Innerspace (1987), similar fluid techniques were used to represent the interior of the human body. According to ILM’s page, they used miniatures to create submersible pods that were then “predominantly shot in the cloud tank to create the liquid look of the internal environment”.
Then there is the Stargate.
PORTALS AND THE DIGITAL ERA
Another memorable use of practical liquid effects in science fiction is the famous “kawoosh”: the violent shockwave erupting outward as the portal activates.
“I remember watching the film and being amazed by the visual effects (...). How did they do that? It looks so real. But it has to be CG, because everything is CG. And as we did the research, of course, it wasn't — they shot it in a big water tank. And we did ours exactly the same way”, John Gajdecki, VFX supervisor for Stargate SG-1’s first two seasons.
The effect for both the movie and, later, the series was achieved using a water tank with compressed air fired very close to the surface. Filmed at high speed, the interaction between pressure and water created the expanding cylindrical wave that gave the portal its explosive, dangerous feel.
However, as digital effects became more advanced, cloud tanks were gradually replaced by digital simulations. CGI offered something these physical setups never could: full control. Direction over movement, light and camera angles.
Practical tank effects offered far less flexibility once filmed, as Gajdecki recalls in an interview with The Companion: “Back in those days, you couldn’t do a lot of perspective-shifting with it. So, we chose four angles and we shot the Gates in those four angles, (...) and if the directors didn’t want to do that, it’s like ‘Well, that’s really great. That’s a really good angle. Why don’t you shoot one from this angle, too?’ And we’d make sure that we’re covered”.
Still, even in fully digital pipelines, the logic of these experiments never really disappeared. For example, in Prometheus (2012), MPC shot stills of ink swirling in water and combined them with high-resolution Earth photography to build the planet's atmosphere as a massive matte painting, as explained by visual effects supervisor Charley Henley on FXGuide.
Because even in modern pipelines, realism rarely comes from invention alone. It comes from reference.
The infinite, it turns out, is easier to fake when it begins with water in a tank.
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