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An Article from the June 2004 JOM: A Hypertext-Enhanced Article

Kelly Roncone is editorial assistant/staff writer for JOM.

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Things that Go Boom in the Night: The Art and Science of Fireworks

Kelly Roncone

Figure 1. White fireworks are typically created using aluminum, titanium, or magnesium. Photo courtesy of Zambelli Fireworks Internationale, New Castle, Pennsylvania.


Figure 2. Blue fireworks, created using copper, are the most difficult of the primary colors to make. Photo courtesy of Fireworks by Grucci, Inc., Brookhaven, New York.



 

 

 

 

 

 

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Figure 3. These diagrams show cross-sections of (a) a multi-break shell and (b) a single-break chrysanthemum shell. Illustration by Mark Spielvogel, Zambelli Fireworks Internationale, New Castle, Pennsylvania

Figure 4. Approximately 1,000 pixel burst shells create the 1,500-foot Transient Rainbow over New York’s East River. Photo courtesy of Fireworks by Grucci, Inc., Brookhaven, New York.

Wooden frames laced with complex designs are stacked throughout the workshop of Mark Spielvogel, a graphic artist at Zambelli Fireworks Internationale in New Castle, Pennsylvania. During a show, the elaborate designs will be illuminated by small fireworks. In another building on the Zambelli lot, during the winter months, Pyrotechnician Bill Gallentine dresses in protective clothing complete with face mask to mix the exact chemical combinations needed to create the reds, greens, oranges, yellows, and blues of fireworks. The fireworks industry is precisely this: a mixture of art and science that results in explosive performances. The art of the fireworks display has expanded in recent years with the development of computerized firing systems and fireworks that burst at the command of a microchip. However, the basic chemistry behind fireworks remains relatively unchanged. The brilliant and carefully choreographed displays of fireworks that are used around the world to signify celebrations are, at their core, a basic reaction between metals and oxidizers.

THE SCIENCE BEHIND THE ART

The Chemistry of Color

The colors seen during a fireworks display are produced by heating metals and salts at the right temperatures to give off specific colors. While each manufacturer has its own recipe for creating color, the basic metallic elements that are mixed with oxidizers to create fireworks are relatively standard. Strontium is used to produce red fireworks; barium to produce green; sodium to produce yellow; copper to produce blue; and aluminum, magnesium, and titanium to produce white (Figure 1).

In each instance, the metals are mixed with an oxidizer, typically chlorates, perchlorates, or nitrates. Water is then added to the mixture to bind the metals and oxidizers together, and the damp mixture is formed into a loaf, which is then cut into smaller pieces called stars. Because the stars contain their own oxidizers, once ignited, they cannot be extinguished until they have burnt themselves out. Oxidizers, which contain excess oxygen, are used to obtain the proper temperature for the reaction. Part of the oxygen will combine with the metal to form a metal oxide, while some of it will combine with the fuel source, which is generally carbon and sulfur based, according to Paul Worsey, who teaches Commercial Pyrotechnics Operations, the only for-credit college course on pyrotechnics in the United States, at the University of Missouri–Rolla.

“This is probably where the art of it is, to get the right temperature for your reaction. Some colors are pretty easy, and those colors would be red and green, but you can tell how good a firework manufacturer is by the quality of their blues,” Worsey said. Blue fireworks, made from copper oxidizers, are generally acknowledged to be the most difficult color to produce because the temperature of the reaction has to be perfect (Figure 2). “It’s the coolest color to burn, so if you use too much or too rich of an oxidizer with the copper combination, you burn it too hot and it becomes a powder blue, meaning it’s washed out,” said Phil Grucci, executive vice president of Fireworks by Grucci, a fireworks manufacturing company based in Brookhaven, New York. “If you burn it too cool, then it either doesn’t ignite or it doesn’t look blue; it looks like an orange-red.”

As with painting, different colors of fireworks are made by mixing the elements that create the primary colors. For example, the copper oxidizer used to make blue fireworks is combined with a certain amount of the strontium used to make red fireworks to create explosions of purple. To create pastels, according to Worsey, white-light generating elements are added to a firework’s composition.

Explosive Effects

In addition to the type of metal, the size of metal particles can determine the look of a firework. For example, a willow or a waterfall firework is one that explodes in the air and then drifts slowly to the ground leaving a trail of color, while a salute or report is a quick burst of light accompanied by a loud sound. The long-lasting fireworks use charcoal because it burns at a slower rate. It also uses larger flakes of metals such as aluminum, because these burn for a long time. In a salute, however, the metal is ground to a fine powder so that it will explode in a burst of light and burn itself out quickly. In a salute, an oxidizer and an aluminum powder are mixed to create a silver color, and titanium is added to the salute to create a sparkling effect, according to Gallentine.

“For the sparks, we wrap burning particles. The particle size and the fuel determine the quantity and size. We use fine fuel particles for heat production, but if we want a sparkling effect, we use larger particles,” said Worsey. In creating fireworks shells, manufacturers fill a cardboard tube with stars, which provide the fireworks color, and black powder, a mixture of potassium nitrate, charcoal, and sulfur. (See the sidebar for details on fireworks manufacturing.) A time-delay fuse that runs into the firework ignites the black powder, which causes the shell to burst open and helps to ignite the stars. Firework shells can house either several effects in a single shell called a multi-break shell (Figure 3a) or a single effect, such as a chrysanthemum (Figure 3b), which explodes to send out stars in a shower of color. The multi-break shell in Figure 3 shows a firework that will produce both the loud flash of white found in a salute or report as well as stars of color. Some fireworks create recognizable shapes in the sky, such as rings, stars, and hearts. These fireworks look similar to the chrysanthemum and other fireworks from the outside, but inside the stars are arranged, using a plastic mold, in the shapes they are to give off (such as hearts or rings). When the firework explodes in the sky, the stars will break out in this same shape.

FIREWORKS GO HIGH TECH

While fireworks were once manually lit by workers, their launch can now be synchronized with music and set off from a distance by computer control. Microchips on individual fireworks can control the exact spot where a firework will explode in the sky, giving pyrotechnicians new creative opportunities.

Microchip-Controlled Fireworks

Fireworks by Grucci uses computer chips in place of traditional firework fuses to control precisely when the pyrotechnic material in a firework will ignite. With traditional fuses, a slow-burning fuse is lit when the firework is launched and is timed to reach the center of the shell—causing the shell to explode—when the firework reaches a certain height. With the computer chip, however, the sequence that passes current through the ignition wire is controlled to ignite the firework at a specific time. The computer chip allows more accurate control of the point where a firework ignites than a traditional fuse.

Grucci uses this technology to create what he calls pixel bursts in the sky. Multiple well-placed pixel bursts can be timed to explode at the same time at specific points in the sky to create an image, such as a rainbow to celebrate the move of New York City’s Museum of Modern Art from the Manhattan area of the city to Queens (Figure 4). This project led to an invitation to create a display for the 150th anniversary of New York’s Central Park in 2003. For this project, Fireworks by Grucci created a 300-meter halo of white lights over the park.

“For the Central Park project, it was all aluminum and titanium,” said Grucci. “The aluminum creates the very bright white flash; the titanium in the coarser particle size creates the snowball aspirations and creates a larger dot in the sky because of the particle size and the purity. We use quite a lot of metals in our pyrotechnics, but by and large, the pixel burst is made with aluminum and titanium.”

What’s next? Grucci plans to refine the pixel burst technology to create more complex displays. Instead of static images, he would like to ultimately be able to create animated sequences, such as writing script in the sky. Until the company’s busy season—U.S. Independence Day celebrations on July 4—is over, however, R&D work is put on hold. “We do more than half of our yearly revenues in that one weekend, so if we haven’t developed it by now, it’s not being used for the Fourth of July,” Grucci said.

Computer-Launched Fireworks

The use of computers to launch modern fireworks has given show designers a greater amount of creativity as well as increased safety for pyrotechnicians. According to Worsey, whose pyrotechnic students often perform fireworks shows at local events, computer programs now allow shows to be run entirely from music. The process of setting a show to music begins by measuring the amount of time a particular type of firework takes to explode after leaving the ground and recording this number in a database. Next, the music to be used in a show is translated to time code, so that it can be read by the computer. From there, show designers must simply determine when they want specific types of fireworks to detonate during the show, and using the database, the computer will calculate how far in advance it needs to launch a firework so that it will explode at just the right time. Once the program is set, the fireworks are grouped together and numbered, connected with Ethernet cables, and then commanded by the computer when to fire, based on the time code.

“It’s becoming very, very technical,” said Worsey. “And it’s becoming a lot safer, since you don’t have people lighting the fireworks and blowing themselves head over heels.”


SAFETY FIRST: A LOOK AT THE
MANUFACTURING OF FIREWORKS

No machines or large buildings dominate the manufacturing facility at the headquarters of Zambelli Fireworks Internationale in New Castle, Pennsylvania, one of the largest fireworks manufacturers in the world. Instead, the company produces and organizes its products in a series of small buildings spread out over approximately 400 acres of the company’s 700-acre lot.

Safety is a key consideration in every aspect of the company’s manufacturing process. Everything from the structure of the buildings to the clothing worn by employees is regulated by strict safety concerns. The buildings are designed to explode with as little damage as possible to the surrounding area. The walls are made of reinforced concrete and the ceilings are made of wood, so that in an explosion, the main force of the explosion will blow up rather than out to minimize the damage to the surrounding area. Employees must wear non-synthetic clothing and rubber-soled shoes to reduce the possibility of creating sparks (Figure A). Needless to say, there is no smoking on Zambelli property.


Figure A. Louis Zambelli assembles fireworks in one of the many buildings on the Zambelli Fireworks lot. Zambelli creates approximately 120 fireworks in three to four hours each day.

Figure B. Aerial firework shells wait at the Zambelli shipping center to be packed into shows. (Photos used with permission of Zambelli Fireworks Internationale New Castle, Pennsylvania.)

Most of the fireworks are assembled during the winter months on the Zambelli lot. This, too, is for safety purposes. In the summer time, when humidity gets low and heat goes up, static electricity is more likely to build up, making accidents more likely. It is also for practical reasons; the company is busy preparing shows during the summer months. Zambelli performs more than 1,000 shows for U.S. Independence Day celebrations in the beginning of July.

In one large building called the shipping center, employees collect and arrange already produced fireworks and package them in specifi c combinations (Figure B). For scripted shows, in which fireworks are set to detonate in time with music, each shell must be numbered before it is packed for shipment to a show destination. In early June, many of the storage facilities scattered throughout the Zambelli lot are already filled with packaged fireworks shows waiting to be loaded onto a truck and shipped to their final destination.

When the busy season ends, crews will return any shell that does not launch during the show to the Zambelli plant for repair or disposal. Disposal is a costly and time-consuming process that Ron Wethli, safety manager at Zambelli, tries to avoid whenever possible. If the shells cannot be repaired, they must be soaked for 72 hours in kerosene and then burned under the supervision of two employees. In the case of shells that have gotten wet, there is no chance of repair. Wet shells must not be allowed to dry out, according to Wethli. Once wet, they must be kept wet and returned to the Zambelli plant for the time-consuming process of destruction. If allowed to dry, there is a possibility, though small, for the shells to spontaneously combust.


Copyright held by The Minerals, Metals & Materials Society, 2004

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