Cloud Tank effect

People have been asking me to provide some of the details of the Cloud Tank so that's been on a long list of subjects. Recently I had to write up some of the notes so thought i'd post it here as well.

When I start in visual effects I was hired by Doug Trumbull as his assistant. The first day I was asked to create clouds in a liquid for a film that he had just started working on called Watch the Skies. You may remember it by the final film title, Close Encounters. They needed to create clouds and they liked the look of pouring cream in your tea or coffee.

I was given a 20 gallon aquarium and $20 of petty cash. I worked in out in a few days with additional ideas from Doug, Wayne Smith and others.

This same process was later used in a number of films and commercials. (Raiders of the Lost Ark, James and Giant Peach, ID4, etc) Actually most of these used the same exact tank as well.

I've attached a couple of primitive drawings to make it clearer. My photos are packed away deep in boxes otherwise I'd post some here. This was also covered to some extent in the Close Encounters book.

Process in a nutshell as used on Close Encounters:
2000 gallon glass tank approx 7 x 7 x 4 feet deep

Water was purified and filtered in 2 large hot tubs/wine tubs(?) 1000-2000 gallons in size.
One had rock salt added (probably close to seawater specific gravity but I can't remember the details)
The salt water was pumped in first usually to halfway mark, dependent on the shot.
Sheet of thin plastic (visqueen) was laid on top. This was longer than the tank front to back and would drape out the back of the tank.

A PVC pipe running the width of the tank was placed on top of this with a rig. Later to remove the plastic it would be pulled out and this PVC pipe was used to keep it down.
A PVC piping system that looked like a fork from above was placed just above the plastic and the fresh water was pumped in.
When done this was removed and the thin plastic sheet was removed.

Now it appeared as just a tank of water but there were two layers if you looked very carefully.
A large syringe was used with aquarium tubing to add small forced perspective clouds in the distance.
The mixed white tempera paint was injected right above the slat water layer. if it went below the tank was contaminated and would require a full redo.

Next an atomic arm was used to inject the main clouds during shooting. This allowed the operator to stand in front of the tank near the camera and as they move it around a brass tube was moving in the tank.
An electric trigger on the handle would cause the tempera paint to be injected as the arm was moved. The tube came from a pressure cooker filled with the paint.

Pressure was supplied from a compressor and an electronic valve was connected to the atomic arm trigger.
We also had a light source (with rotating colored lights) that went down this same tube as a fiber optic.

Frame rates could be under cranked or over cranked depending on the look.






Close Encounters Book

Close Encounters - BluRay

Close Encounters - DVD