By Paul E. Smith Read 3 Minutes
In the earliest days of the United States, John Adams wrote to his wife Abigail about the celebration of Independence: “It should be celebrated with Pomp and Parade, with Shews, Games, Sports, Guns, Bells, Bonfires and Illuminations of one end of this continent to another from this time forever more.” “Bonfires and lighting” refer directly to what we know today as fireworks and fireworks.
I am a chemist and also president of Pyrotechnics Guild International, an organization that promotes the safe use of fireworks and uses it here in the US to celebrate Independence Day and other festivals throughout the year. As a chemist and someone who leads demonstrations for chemistry students, I consider fireworks to be a great example of combustion reactions that produce colored fire. But the invention of colored fireworks is relatively recent and not all colors are equally easy to make.
Early history of fireworks
Firecrackers were first accidentally invented by the Chinese in 200 BC. But it wasn’t until a thousand years later that Chinese alchemists developed fireworks in the year 800 AD. These early fireworks were mostly bright and noisy concoctions designed to deter evil spirits — not the colorful, controlled explosions we see today. Fast forward another millennium, and the Italians discovered how to add color by adding different elements to the flammable mix. Adding the element strontium to a colored pyrotechnic mix creates a red flame; copper, blue; barium, green; and sodium for yellow.
Too much or too little of the chemicals will cause significant changes in the temperature and thus in the wavelength of the color being perceived. The right mixture of chemicals, when ignited, produces enough energy to excite electrons to give off different colors of light.
While the chemistry of these colors isn’t new, every generation seems to get excited by the colors splashing through the air. We now have a wide variety of flame colors: red, green, blue, yellow, purple and variations of these.
Each color works the same way. When different elements ignite, they give off different wavelengths of light, which translates into different colors.
Making that perfect blue fireworks
Not all colors of fireworks are equally easy to make. I believe several of my colleagues in pyrotechnic research and development agree that blue is the most difficult color to produce.
That’s because the evening sky has a blue tint, which means that most shades of blue aren’t very visible. If you try to brighten the blue to contrast with the background, it may appear faded. The right balance of copper and other chemicals in the flame or combustion reaction produces the best blue flame color in fireworks.
I took this into account when creating the best flame blue color, which I call pillbox blue. It’s just bright enough to stand out against the night sky, but still a rich blue. I have over 20 blue pyrotechnic formulas and I have found one that comes very close to this elusive shade.
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 activated in the flame. When the electrons release this energy, it appears as blue light to observers. Each color works the same way. When different elements ignite, they give off different wavelengths of light, which translates into different colors. So when you see blue colored points of light creating a pattern in the night sky, you see really excited electrons releasing energy as blue light.
Paul E. Smith is a college chemistry demonstrator at Purdue University.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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