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Pyrotechnics

Pyrotechnics is a field of study often thought synonymous with the manufacture of fireworks, but more accurately has a wider scope that includes items for military and industrial uses. Items such as safety matches, oxygen candles, explosive bolts and fasteners, and the automobile safety airbag all fall under the purview of pyrotechnics.

The use of explosions, flashes, smoke, or flames on-stage is known as Proximate Pyrotechnics.

Many musical groups will use pyrotechnics to enhance the quality of their live shows. The band Rammstein uses such large variety of pyrotechnics, from flaming costumes to face-mounted flamethrowers, that their fame is based largely on their use.

Generally, pyrotechnics can be divided into categories based on the device's main effects, among them bangs, flashes, flames, or smoke. A basic non-firework pyrotechnic device generally consists of a container to hold the materials, of an obviously hazardous nature, and a fuel, and an oxidizer, as well as additives to increase the strength of the bang or the flash.

Pyrotechnics use a variety of chemistry concepts, which produce different effects of sound and color. Although fireworks are pyrotechnics, not all pyrotechnics are fireworks. Pyrotechnics include any effect that uses rapid oxidization to produce an effect of light or sound. This excludes almost all high explosives except for a very few used in pyrotechnics such as picric acid. Thermite reactions and decomposition of ammonium dichromate2 are never used in commercial fireworks but they can be pyrotechnic displays.

An important part of pyrotechnics to the amateur is synthesis of different chemicals to be used in certain reactions.

Often chemicals cannot be acquired for reasonable prices, so the chemicals are manufactured at a home lab. There are a wide variety of chemistry principals that apply to pyrotechnics and making different chemicals for pyrotechnic use.

These include the use of the periodic table and of course the elements, polyatomic ions and compounds, ionic, molecular compounds, hydrocarbons, synthetic substances, and sometimes balancing equations. They also include synthesis and decomposition reactions, double and single displacement reactions, controlling rates of reactions, endothermic and exothermic reactions, acids and bases, and element oxides. Of course combustion is a central part of pyrotechnics and is dealt with throughout the other topics instead of being given its own section.

Chlorates are useful in most types of colored fire composition.

Their large oxygen content is useful for starting the chemical reaction, and the ions they yield produce the color that is desired. For instance: mixing barium chlorate and orange shellac, a binder / fuel resin that is basically a complex carbohydrate with some trace elements, can produce a green flame. Potassium chlorate, orange shellac and strontium compounds can produce red flames. A stable and safe formula for white, blue and purple flames was developed in the 20th century. Before this time, the majority of recipes was unsafe and needed to be precisely mixed for them to work properly. The modern firework generates white flames with the addition of antimony and aluminum dust to potassium nitrates and some sort of fuel, such as charcoal or shellac. Blue coloration is generally achieved with the use of copper, sulfur and potassium compounds.

Oxidizers
The first thing in a firework is the oxidizing agent. These produce the Oxygen to burn the mixture. Oxidizers are usually nitrates, chlorates or perchlorates. The common oxidizers are nitrates. These are made up of a metal ion and the nitrate ion. I'll use potassium nitrate as an example. Nitrates only give up 1/3 of their oxygen. The resulting equation would look something like this:

2XClO3 -› 2XCl + 3O2

The next Oxidizers are chlorates are also made up of a metal ion and then the chlorate ion. Chlorates give up all of their oxygen, causing a more spectacular reaction. Unfortunately this also makes the chemicals EXTREMELY explosive. An example of a chlorate giving up its oxygen would look something like this:

XClO4 -› XCl + 2O2

Perchlorates have more oxygen in them, but are less likely to explode if you drop them than are chlorates. Again these are made up of a metal ion and then the perchlorate polyatomic ion. An example of a typical perclorate giving up its oxygen would look something like this, (graphic).
Reducing Agents

The second elements of fireworks are the reducing agents. The reducing agents burn the oxygen produced by the oxidizers to produce hot gasses. Two examples of reducing agents are Sulfur and Charcoal (carbon). These react with the oxygen to form respectively Sulfur Dioxide and Carbon Dioxide.

Binders
The fourth element of fireworks is the binders. Binders hold the mixture in a lump. This lump is a star. In order to form a star, two main elements are used. These two are dextrine dampened by water, or a shellac compound dampened by alcohol. These are rolled and then cut, or the mixture is forced into a paper tube, and pushed out with a dowel. Then the stars are cut as they come out.

Creating firework colors is a complex endeavor, requiring considerable art and application of physical science. Excluding propellants or special effects, the points of light ejected from fireworks, termed 'stars', generally require an oxygen-producer, fuel, binder (to keep everything where it needs to be), and color producer. There are two main mechanisms of color production in fireworks, incandescence and luminescence.

Incandescence

Incandescence is light produced from heat. Heat causes a substance to become hot and glow, initially emitting infrared, then red, orange, yellow, and white light as it becomes increasingly hotter. When the temperature of a firework is controlled, the glow of components, such as charcoal, can be manipulated to be the desired color (temperature) at the proper time. Metals, such as aluminum, magnesium, and titanium, burn very brightly and are useful for increasing the temperature of the firework.

Luminescence

Luminescence is light produced using energy sources other than heat. Sometimes luminescence is called 'cold light', because it can occur at room temperature and cooler temperatures. To produce luminescence, energy is absorbed by an electron of an atom or molecule, causing it to become excited, but unstable. When the electron returns to a lower energy state the energy is released in the form of a photon (light). The energy of the photon determines its wavelength or color.

Sometimes the salts needed to produce the desired color are unstable. Barium chloride (green) is unstable at room temperatures, so barium must be combined with a more stable compound (e.g., chlorinated rubber). In this case, the chlorine is released in the heat of the burning of the pyrotechnic composition, to then form barium chloride and produce the green color. Copper chloride (blue), on the other hand, is unstable at high temperatures, so the firework cannot get too hot, yet must be bright enough to be seen.

Quality

Pure colors require pure ingredients. Even trace amounts of sodium impurities (yellow-orange) are sufficient to overpower or alter other colors. Careful formulation is required so that too much smoke or residue doesn't mask the color. With fireworks, as with other things, cost often relates to quality. Skill of the manufacturer and date the firework was produced greatly affect the final display (or lack thereof)


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