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Spectroscopy and the science of fireworks

Comedian Jim Gaffigan once mused, “I don’t normally eat a burger, a brat and a steak, but it is the Fourth of July – and I’ll need the energy if I’m going to blow stuff up later.”

Fireworks are an essential part of any Independence Day celebration. But have you ever stopped to consider exactly how those dazzling pyrotechnics work? The science behind fireworks is far more interesting than that of other, simpler explosives. But what do fireworks have to do with spectroscopy – and what is spectroscopy, anyway? This article will cover all that and more, but first let’s take a deeper look at where fireworks originated and why the science behind them is so fascinating.

Fireworks: From ancient invention to modern marvel
The fireworks you might see at a Fourth of July concert or a city-sponsored display are a far cry from the original invention. Though the exact origin is still disputed, many historians believe fireworks first came about as early as 200 BC in the Han dynasty of ancient China, according to the History Channel. Instead of cardboard casings, the first pioneers used bamboo sticks. When thrown on a fire, the stalks would cackle and explode due to the air pockets trapped within.

“Instead of cardboard casings, the first fireworks pioneers used bamboo sticks.”

When a few clever individuals decided to pack those bamboo chutes with saltpeter, sulfur, charcoal and other compounds, they created a rudimentary gunpowder and produced even bigger, louder and more impressive pops. From there, two separate paths emerged: One side which led to the development of arms and explosives for military uses, and the other side, fireworks for celebrations and special events.

Most of us are aware of how far along military weaponry has advanced since those first bamboo sticks were thrown on a fire, but fireworks technology hasn’t exactly stagnated either. Fireworks eventually grew so popular that John Adams called for their use during what would become Independence Day “from one end of this continent to the other, from this time forward forevermore.” Now, many states have restrictions and regulations surrounding the sale and use of fireworks – they are explosives, after all – but that doesn’t stop Americans from using around 14,000 displays every Fourth of July, according to the American Pyrotechnics Association.

The illuminating science of fireworks
Different groups will create unique fireworks according to their own preferences and “recipes” handed down through the generations. But all of these explosives have a few things in common, according to Science Daily: fuel and a fuse. The fuel usually a mixture of charcoal, sulfur and potassium nitrate, not far from the black powder used by the first fireworks pioneers. In the tube itself are packets full of powdered metals.

It is the combination of these metals that creates the variety of colors in fireworks. When the explosion occurs, the packets burst and the elements oxidize, creating heat.

“The heat is needed to excite the metal particles so they can emit light,” Stefan Bossmann, chemistry professor at Kansas State University, told Science Daily. “Different metals produce different colors. For example, think of liquid steel. When it gets hot it turns yellow.”

Which metals create which colors? Science Daily organized a cheat sheet:

  • Strontium and lithium: Red
  • Calcium: Orange
  • Sodium: Yellow
  • Barium: Green
  • Copper: Blue
  • Potassium and rubidium: Violet
  • Charcoal and iron: Gold
  • Titanium, aluminum, beryllium or magnesium: White

For those pyromaniacs in the audience, beware – homemade fireworks aren’t a great way to host a Fourth of July picnic. It is not enough to dump random metal powders into a tube and light it on fire. In fact, doing so will probably get you arrested, injured, or otherwise in a mess of trouble. Safety should always be the primary concern when you’re watching, lighting or researching how to manufacture fireworks.

But why do certain metals glow a specific color when oxidized?
A great question, and one which requires a closer look at the science behind fireworks.

Each atom has a unique and distinct emission spectrum. That means when faced with great heat, an element will show its true color – literally. It must be one of the more poetic aspects of physical science that each element will glow a certain color when it becomes excited. Polymer Solutions’ Applied Chemistry and Spectroscopy Lab Manager Alan Sentman, Ph.D., explains more in the video below:

Emission spectrum analysis doesn’t exist so we may all enjoy spectacular fireworks over a beer and a hamburger. Instead, scientists like Sentman can use tools like the Inductively Coupled Plasma Optical Emissions Spectrometer to find elements that are out of the ordinary. By identifying an element’s spectrum, scientists can also infer certain characteristics and attributes of that element, including its identity.

In material analysis, the ICP-OES and other spectroscopy tools help labs gauge products or materials and learn how they react under certain conditions. Specifically, these methods can reveal which elements are present in a sample, how much of a specific compound is there, what type of degradation has occurred and a bevy of other insights.

So when you sit down at the picnic table, head to the lake house, watch the parade or even enjoy a view of the fireworks from a distance, take a moment to consider the astounding physics occurring before your very eyes. It might be fun to think of the reaction as a magical, unexplainable phenomenon, but in this case, the science behind it makes it even more enjoyable.