By Paul E. Smith 3 minutes Read on
In the earliest days of the United States, John Adams wrote to his wife, Abigail, about the celebration of independence: “It should be solemnized with grandeur and parade, with shows, games, sports, guns, bells, fires, and illuminations. from one end of this continent to the other from this time forward forever more.” “Fires and illuminations” refers directly to what we know today as pyrotechnics and firework displays.
I am a chemist and also president of Pyrotechnics Guild International, an organization that promotes the safe use of fireworks and their use here in the US to celebrate Independence Day and other festivals throughout the year. As a chemist and someone who conducts demonstrations for chemistry students, I consider fireworks to be an excellent example of combustion reactions that produce colored fire. But the invention of colored fireworks is relatively recent, and not all colors are easy to produce.
The early history of fireworks
Fireworks were first invented by the Chinese in 200 BC. But only a thousand years later, Chinese alchemists developed fireworks in 800 AD. These early fireworks were mostly bright and noisy inventions designed to scare away evil spirits – not the colorful, controlled explosions we see today. Fast forward another millennium, and the Italians figured out how to add color by introducing various elements into the flammable mixture. Adding the element strontium to a colored pyrotechnic mixture produces a red flame; copper, blue; barium, green; and sodium for yolk.
Too much or too little of the chemicals make significant changes in temperature, and thus in the wavelength of the color seen. The right mix of chemicals when ignited produces enough energy to excite electrons to emit different colors of light.
Although the chemistry of these colors is not new, every generation seems to be excited by the colors scattered across the sky. Now we have a wide range of flame colors: red, green, blue, yellow, purple and their variations.
Each color works the same way. As different elements are lit, they emit different wavelengths of light, which translate as different colors.
Making that perfect blue firework
Not all colors of fireworks are equally easy to create. I believe some of my colleagues in pyrotechnic research and development would agree with me that blue is the most difficult color to produce.
That’s because the evening sky is a shade of blue, which means most blues don’t show up as well. If you try to make the blue brighter in contrast to the background, it can look washed out. The proper balance of copper and other chemicals in the flame or combustion reaction produces the best blue flame color in a firework.
I’ve taken this into account when trying to create the best blue flame color, which I call pillbox blue. It’s bright enough to stand out against the night sky, but still a rich blue. I have over 20 blue pyrotechnic formulas and have found one that comes very close to this elusive color.
Another difficulty in creating an intense blue color is that the chemistry is not simple. It requires a combination of several chemicals and the element copper. When copper ignites, the electrons surrounding the copper atoms are excited and gain energy in the flame. When electrons release this energy, it appears to observers as blue light. Each color works the same way. As different elements are lit, they emit different wavelengths of light, which translate as different colors. So when you see blue dots of light creating a pattern in the night sky, you’re really seeing excited electrons emitting energy as blue light.
Paul E. Smith is a Lecturer in Chemistry at Purdue University.
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