Cloud Tank Questions

Can anyone help with some cloud tank questions? Shooting standard coloured fluids in a fish tank stuff. Not really looking for clouds, just psychedelic patterns to use as backgrounds for VFX.

1. Temperature. Do you heat the coloured fluid and chill the water?
Is it the other way around? How does temperature effect the dispersion of the fluids?

2. Is it better to use lights that don't generate much heat? Like the LitePanels LED system?

3. What are the best coloured fluids to use? Paint? Dye? Human Blood?

Sorry, I looked in a bunch of books but could not find any practical data. Thanks in advance for any advice.

Alan Lasky
People's Republic of California

I've done quite a few tank/dye shoots, but I'm not a vfx guy.

Generally temperature of fluids didn't seem to be an issue on any of my shoots.

Heat from the lights was never an issue.

What fluids to use? All have different effects. Basic dye from the art store works great. Oils in water and vice-versa (different viscosity and weight) make for interesting effects.

Other things to consider :

Put the water tank on a rocker plate, or use a paddle to agitate the water.
Backlight and cross light generally look better to me some fluids take well to large source lighting for sheen, others to hard light for distinct shadows and edges. sometimes I underlight the tank, very effective for some fluids.

You may need several tanks so you don't waste time dumping and refilling.
I request GLASS, not plexi. plexi is optically less clear, and scratches, and attracts dust due to static.
I sometimes request custom narrow tanks, with only 6 inches between front and back, so I can work with a low volume of water.

Consider your DOF, you may need more light than you think to carry the focus.

also, HOW the liquid is put into the tank is crucial.

Try : an eyedropper from one inch, from 2 feet, or injecting dye from a syringe (my favourite) pour from a pitcher dribble down edges of glass

Good luck, it's fun!

Andrew Turman
dp
Santa Monica

Alan Lasky wrote :

>>Is it the other way around? How does temperature effect the dispersion of the fluids?

I experimented with this sort of thing many, many years ago and iirc relative temperature has a variety of interesting effects on 'miscibility'. Heat exchange between the dye and the water creates eddies and swirls past the point that the momentum of pouring one liquid into another does that anyway.

I can only suggest you try out a bunch of stuff on the kitchen table with a Pyrex bowl filled with water. From memory we had fun making an extremely saturated salt solution (common table salt) and depositing a layer of fresh water on top of it (using a sheet of paper to prevent too much mingling, then carefully sliding it out). Dye would hit the invisible division in the water and spread around in a cool way. Detergents did weird things too. Colourless mineral oil and white spirits as either a medium for the dye or as a layer sat on water did similar things.

Higher frame rates help a lot too.

Tom Townend,
Cinematographer/London

Alan,

We did this several years ago to bookend our demo reel and create elements for our website:

http://www.dzignlight.com/ourwork.shtml

My biggest suggestion, beyond what has already been mentioned, is to make sure you have a way to get a lot of water in and out of your set quickly. You can only do a few runs before the water starts getting coloured and then you have to swap it all out. If filling the tank takes 10 minutes you are going to be standing around a lot.

Regarding coloured fluids, we brought a lot of different substances to the table but basic food colouring ended up having the look we liked...
and it was easier to clean up than anything else.

Also, it wouldn't hurt to bring a roll of screen mesh to put in the tank as you are filling it, to cut down the motion of the water. We found that, without something in the water creating friction, it took many minutes for the momentum of the filling process to dissipate.

Have fun with your shoot!

Eric Deren
Dzignlight Studios
VFX & Animation Design
www.dzignlight.com
+1-404-892-8933

>>My biggest suggestion, beyond what has already been mentioned, is to make sure you have a way >>to get a lot of water in and out of your set quickly.

When I was working with Roy Field on Superman (yes I'm that old!) this was a real problem. We were using one of the big tanks at Shepparton (about 20' long). I seem to remember that the SFX boys were using emulsion paint to imitate exploding galaxies. Two takes and that was it for the day!

Brian Rose
Technical Consultant
Tel: +44 (0)20 8868 1729Mob: +44 (0)7768 635 788

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