The Chemistry of Special Effects in the Film Industry

When talking of special effects in films, certain blockbusters come to mind. Films like Titanic, and The Matrix, Lord of the Rings, and Spider-Man trilogies have been lauded for their effects. Although some of these effects are traditional, when looking at science fiction and action films released in the past 10 years, it is obvious that special effects have shifted out of traditional effects into computer technology. For the most part, the science-fiction and action movies of today's film industry utilize Computer Generated Imaging (CGI). It is only when one looks at more realistic and contemporary films such as Ladder 49 and Backdraft that the amount of chemistry involved in film effects becomes apparent.

In recent years, computer technology has replaced almost all special effects, but some effects remain solely chemically created. Out of all the on-set effects, smoke and fire -two of the most important effects used these days - are created by chemistry. In the firefighter film Ladder 49, scene after scene of burning buildings needed more realism than computers could provide. For this purpose, Propane (C3H8) mixed with small amounts of other fuels (to add soot and color to the clean flame of propane) was burned. It was originally thought that computers could simulate the fire in Ladder 49, but the visual effects lacked the realism needed.

Another major part of films is smoke and fog machines. These machines have been used in all kinds of movies, from the musical romance Moulin Rouge to the science-fiction film War of the Worlds. These machines can work three different ways. The first is with dry ice (frozen CO2) and hot water. Although this method is used more in the theater, it can still be effectively used for film. However, the gaseous CO2 product can decrease the O2 levels in the air around, so only certain amounts can be used at a time.

The second method used uses liquid nitrogen (N2). One of the big advantages of liquid nitrogen is that nothing extra is needed to produce fog, as exposing the N2 to a warmer temperature causes it to revert to its gaseous form at an increased rate, cooling the air and causing water to condense. Liquid N2 is cold enough to cause frostbite and cold burn, so caution must be taken when handling it. As with the dry ice method, when the O2 concentration in the air is sufficiently low, a person can become unconscious without sensing any warning symptoms, such as dizziness. Because of this, care must be taken with both of these methods.

The third method of producing fog, and the most versatile, is that using atomized glycols. Many commercial smoke machines use 'fog juice' that consists of glycols, glycerin, and/or mineral oil, with varying amounts of distilled water. The glycols are heated and forced into the atmosphere under pressure to create a fog or haze. Up to 35% food grade glycerin (C3H8O3) to each liter of glycol/distilled water mixture creates a 'haze' at concentrations of 15% or less and more of a fog or smoke at concentrations higher than 15%. However, the smell created by this is unpleasant, and so unscented glycols with water are used more in films. A mixture of 10% distilled water and 90% propylene glycol (C3H8O2) creates dense fog. 40% distilled water and 60% propylene glycol works for quick dissipation. 30% distilled water, 35% dipropylene glycol (C6H14O3) and 35% triethylene glycol (C6H14O4) creates very thick fog.

With all the recent developments in visual effects, it is likely that even these effects may someday be generated with computers. However, for the moment, the most realistic methods for rain, smoke, fog, and fire remain as on-the-set, realistic effects. There is no doubt that without the chemistry involved, many movies from every time period would be without the effects that simulate some of the most amazing natural phenomena.

Works Cited:
Arnold, Richard L. Scene Technology: Third Edition. Englewood Cliffs, NJ: Prentice-Hall, Inc, 1994.
Young, Robyn V. World of Chemistry. Farmington Hills, MI: Gale Group, 2000
http://chemistry.about.com/library/weekly/aa010603a.htm
http://www.kryogenifex.com/
http://science.howstuffworks.com/fire1.htm
http://www.bpnews.com/htmlfile/special/ladder49.htm
http://www.scienceinthemovies.com/