As Fourth of July approaches, most people will enjoy a beautiful view of glistening fireworks in the sky. The “oohs” and “aahs” at every bold color combination can be heard a mile away. But… what actually makes up fireworks? Are they safe to use? What is the chemistry behind these light shows?
First, a bit of history. The Chinese invented fireworks somewhere around 960 and 1279 AD. They shot them to ward off evil spirits and used them during celebrations, like the Emperor’s birthdays and Chinese holidays. Fireworks were then used to celebrate independence in the United States on July 8, 1776. They were used in England to celebrate the birthdays of kings and queens. Currently, fireworks are almost synonymous with Independence Day .
One of the most notable parts of fireworks are the vivid colors. How do they come to be? The color is determined by the metal salts that are present in it. The heat that these metal salts experience excites the metal atoms to a higher energy state, and when the atoms relax back to their more stable ground state, they emit colors. The wavelength of light that is emitted when these atoms relax are characteristic of specific atoms: strontium glows red, sodium burns orange, copper burns green, etc .
There are more chemicals involved in the perfect firework. Black Powder is the propellant. It is an old formula made from potassium nitrate, sulfur and charcoal. When it is ignited, the nitrate oxidizes the sulfur and charcoal which results in hot gasses. The Mortar is the container. It is usually a cylinder chamber made of plastic or metal. It can be a short, steel pipe with a lifting charge of black powder in the bottom or surrounding stars. The pyrotechnic compounds that explode and create the colors and effects are simply called “stars”. They are spheres, cubes or cylinders about the size of a pea to a tennis ball. A shell is a hollow sphere made of pasted paper and string. The shell is cut in half and packed with stars, which allows for the pattern to be made when ignited. The bursting charge is one of the most important aspects; it is inside the middle of the shell to ignite the firework. The charge ignites the outsides of the stars, which burn with showers of sparks. Lastly, the fuse allows a time delay for the explosion. Some fireworks even contain perchlorate which enables a louder sound .
How safe are fireworks though? In recent years, regulations have been passed to prohibit use of hazardous materials in the fireworks. They also have more stabilizing factors so that they don’t tip over while ignited. Only three states have heavy regulations on the use of fireworks currently in the U.S. .
Overall, fireworks are simply a fun application of physics and chemistry. Think about the chemistry next time you see the beautiful displays of color on New Years’ Day or Independence Day!
 CBS News. “How Fireworks Work: The Science behind Pyrotechnic Displays.” CBS News, CBS Interactive, 1 July 2014, http://www.cbsnews.com/news/how-fireworks-work-the-science-behind-pyrotechnic-displays/.
 “Chemist Explains the Science behind Fireworks.” Phys.org – News and Articles on Science and Technology, Phys.org, phys.org/news/2017-07-chemist-science-fireworks.html.
 Zagorsky, Jay L. “Analysis | Fireworks Are Fun. But How Safe Are They?” The Washington Post, WP Company, 3 July 2017, http://www.washingtonpost.com/news/posteverything/wp/2017/07/03/fireworks-are-fun-but-how-safe-are-they/?noredirect=on&utm_term=.d3965b51445a.
 Image credit to picjumbo