Liquids

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General principle of operation
This section is intended for studio-based shoots, though some information is also true for larger pool-based shoots.

Liquid shoots can be potentially very dangerous, due to both electrical and slip hazards, spills must be minimised and cleaned up immediately after they occur.

Throughout, the term ‘underwater’ means, immersed in the liquid, whatever it is.

Repeating exact action can be very difficult with liquids, for this reason almost every job will require, (at the very least), simple custom made rigs.

Tanks
Tanks are either existing or custom made and, depending on your needs, can incorporate different features. The more specialised your requirements, the more likely it is you will need a custom made tank, which can be anywhere from a modest cost, to something quite expensive.

When dealing with tanks, be aware of the physical weight and volume of water; a 1 meter square tank of water weighs 1 tonne (plus the weight of the tank) and if it broke, would make a puddle the size of a tennis court and 4mm deep.

If the shoot uses only water, the tank will be filled from the convenient water supply located close by, if you are using water that has been thickened, it is often made up beforehand and brought in or made in the studio on the previous day. Once filled, any further equipment will be installed, this will include items for the effect itself, but may also include, heating, mixing, filtration, re-cycling, pumping and agitation equipment.

A quiet word about actors…
It would be a thankless task to try to cover the great breadth of possibilities when you take liquids out of a tank based environment, however, it often involves actors in baths, showers and sprays of water and pours of gunk.

Generally a shallow catch tank for the liquid will be constructed on the floor of the studio and all the wet work will occur in this tank; this can get very slippery, especially if you are using gunk.

Unless water is heated, any actors getting wet, will get very cold, very quickly; for this reason water must be heated, and there must be lots of towels available. Remember people change colour at different temperatures and after different lengths of time being wet. A steam or smoke generator is often used to make warm water look hot, which helps minimise colour changing problems. Any dyes or pigments may potentially colour your actor and his or her clothes, so undertake tests prior to the shoot.

Technical stuff
Although you would think working with liquids to achieve exact results is relatively easy, it is in fact very demanding, which means we have to deal with the technical and jargon aspects thoroughly. Sorry.

It is generally not possible to film organic liquids or product because they often have undesirable properties, they change under studio conditions over time and can ferment within 12 hours. For this reason, liquids for film shoots are usually water based with additional thickeners and/or colours. Water is chosen as the medium because it is cheap, easy to get, easy to dispose of and the most pleasant to use of all the choices available.

The clarity, opacity and viscosity of water can all be changed to suit your requirements. Water from a tap has a surprising amount of debris in it and should be filtered, and even if it is clean, the air in the studio is not, so the liquid will soon be full of airborne debris, dust, hair etc. This can be removed by filtration throughout the shoot.

Liquids can be coloured either by the use of a dye or a pigment. A dye is a coloured substance, that dissolves fully in the liquid to form a solution. This will form a transparent coloured liquid and will stay like this indefinitely. A pigment is a paste or powder of fine coloured particles that forms a suspension when mixed with the liquid, this will be opaque and will settle out over time. For this reason separation of colours and settling of the particles can occur with pigmented liquids.

If you are using a water-based liquid it is possible to increase its viscosity using thickeners. Liquids are usually made up in advance as they may continue thickening for some hours after being mixed. It must also be noted that it is very difficult to change the viscosity of such a liquid once it has been made, so agree on a sample in advance, prior to the shoot.

It is often necessary to use high-speed camera equipment and playback facilities, with all the attendant lighting, which may include strobe lighting for specialist effects.

For complex liquid effects, it often helps to use computer-controlled timing and activation.

For certain effects water based liquids may not be suitable, in these cases, silicone oil, corn syrup, glycerine or glycerol, mineral oil or spirits may be substituted as common alternatives, these are more expensive, are more unpleasant to use and there may be additional disposal, safety and storage costs.

First considerations
It is very important to have a water supply and drain nearby.

Work out the effect you want, and try to simplify it, this can save you a great deal from your budget, at the same time, try to reduce or remove any re-filling which may be required, because if the tanks are large, it will take considerable time.

Is the desired effect possible under water? Not all effects are. Is the desired effect possible with a liquid? Not all effects are. In these cases it may be possible and indeed easier to make the effect in a dry environment or to make a solid model of the liquid.

Notify the gaffer and the venue about liquids being present; they may have particular requests.

Budget expectations
Generally a crew of two or more effects technicians is required to ensure there are no supply or disposal problems and to act quickly in the case of a major spill.

Depending on what you wish to do, tanks can vary greatly in cost; small glass tanks are cheap, yet large glass tanks with toughened or laminated glass are disproportionately expensive.

Water based liquids do not tend to be expensive, even with thickeners and colours in, however any other choice for a medium will drive the cost up. Be assured these will only be chosen if they really are required.

High-speed cameras and lighting to suit will obviously increase the cost.

Computer controlling of the effects, if required, will also increase the cost moderately.

As a rule if you want to a shoot with a small tank, using water based liquids, the cost will be quite reasonable.

Questions to ask
Can I see your showreel? Have you done jobs like this before? etc
Can I see a sample effect before shoot day?
Am I doing any thing really wasteful and are you able to suggest any money saving changes?
How uncomfortable will it be for the actors?
What emergency clean-up equipment do you bring?
How will my models and rigs perform underwater.
Is it possible to light the liquid so as to change its colour?

Problems to watch out for and things to do
- Watch tests well in advance.
- Ensure that the gaffer and the studio are aware the shoot involves liquids.
- Slip and electrical hazard problems can be caused by spillage, over spray or when working in a catch tank. Electrical equipment in the vicinity should be fitted with RCDs.
- Actor’s health and safety and continuity problems - watch out for them becoming redder, paler or wrinkled due to water exposure. Actors becoming stained by being in contact with coloured fluids.
- The length of time taken to drain and refill tanks if this is required.
- Debris settling on or in the water.
- Reflections from the tank surface can make lighting a lengthy process.
- Ripples made in a tank can reflect back from the sides.
- Hired optically clear tanks being in bad condition.
- Ensure all models and rigs have been properly made for the medium in which they will work.
- They will behave differently under water; parts go rusty, filler can fall out, paint can bubble, plastic parts can swell and models can float.
- The colour balance of models can change and due to refraction, their visual position relative to other objects underwater can also change.
- Before we fill it, can we empty it?

Know the jargon
Agitation Movement used to keep suspensions of liquids and particles mixed
Catch tank Inexpensive, shallow tank constructed on the floor from wood and plastic/rubber sheet
Centistokes The scale used to measure the thickness (viscosity) of a liquid
Dye Mixes with a liquid and changes its colour permanently, but is translucent
Emulsion A suspension of one liquid in another, which usually divides out to form two liquids
(salad dressing is an example)
Filtration Used to remove debris from a liquid before or during use
Flow rate The speed at which a liquid moves
Food thickener Used to thicken water to make it more viscous
Gunk A very viscous mixture of food thickener, water and colour – really slimy and slippery
Head Used to either describe pressure or volume available
Horizon tank Tank made so that the edge away from camera is at the level of the liquid, giving a
false horizon
Impeller Rotating device to spin liquid in tanks or propel it down tubes – it is often, but not
always a propeller
Laminated glass Layered glass sheets – very tough; has a clear plastic middle layer that holds the bits
together if a sheet is broken
Meniscus The curved edge of a liquid where it meets a solid edge
Miscible The ability of one substance to dissolve in another
Opacity/opaque Something you can’t see through
Perspective tank A tank made to mimic the view angle of a lens
Pigment A colouring agent made from fine particles, which form a suspension in a liquid
RCD Residual Current Device – simplistically, a very sensitive fuse which is easily reset
Refraction An effect of looking at an object in a liquid where distances and viewing angles
are altered
Settling The solid part of a suspension falling to the bottom
Solution/soluble A substance which dissolves completely in a liquid
Spirits Generic term for alcohol, thinners, cleaning solvents etc
Stability The ability of a liquid to stay the same under differing conditions for example,
temperature, light levels, age etc
Submersible A pump which works from under the surface of the liquid
Suspension Small particles floating in a liquid – can settle out
Toughened glass Heat treated to become stronger and tougher; used for larger tanks
Transfer pump Pump which works from outside a tank of liquid
Translucency/ Transparency The degree to which you can see through the liquid
Viscous/viscosity Viscosity means thickness
Vortex A very deep whirlpool
Whirlpool A shallow vortex