ST. LOUIS – Fireworks are always a spectacular show. These amazing bursts of colors are all about chemistry.
They start with fuel and an oxidant which is responsible for making the explosion.
Black powder, a mixture of charcoal and sulfur, is the fuel. Saltpeter, or potassium nitrate, is the oxidant. Various metals in that mixture are responsible for making the colors.
Dr. Paul Bracher, assistant professor of chemistry at Saint Louis University explained that the fuel and oxidant make the explosion. The heat that is generated in the explosion excites the electrons in the metals to higher energy levels.
“When those electrons decay back down to their ground states, which they want to do. Then the energy that corresponds to that transition is going to be the energy of a photon of light that’s released and if that energy corresponds to visible light, that’s the light that you see,” said Dr. Bracher.
Different elements have different energy transitions responsible for them. These different elements will impart different colors to the fireworks.
“Strontium gives you red and typically is the one you choose. Lithium could give you a magenta color. Calcium can give you an orangey color. Sodium gives you a very nice yellow color,” Dr. Bracher said. “Barium gives you a green color. Copper typically gives you a blue. And purple is hard. There’s not really anything that gives you a bright purple color. So you typically will mix a blue like a copper blue with like a red.”
Dr. Bracher said that blues and purples are harder than some of the other colors because copper is finicky. The easiest color to create is yellow.
“Sodium’s intensity is just so bright and also our eyes are more sensitive to yellow wavelengths so those show up really well,” Dr. Bracher said.
This color emission principle isn’t just used for fireworks. Dr. Bracher said he uses it in his lab for research as well.
“We have an instrument that has a flame and we shoot solutions that have metals in them like sodium and potassium and then we look at the intensity of their emissions and judge their concentrations based on this. So fireworks just aren’t all fun and games. We use these same scientific principles in the laboratory to do scientific research,” Dr. Bracher said.