As festivals and backyard barbecues spread across Michigan, the sky fills with pyrotechnic 'stars' to celebrate summer. Central Michigan University chemistry professor Gabriel Caruntu explains the science behind the colors of fireworks.
What are fireworks made of?
Fireworks contain five main components:
oxidizing agent: necessary to produce the oxygen required to burn the mixture;
Black powder: used as fuel;
A chlorine-donating compound: to help strengthen some colors;
A binder: to keep everything together; and,
A metal salt: to produce color.
Where does the color come from?
Fireworks contain different chemical elements and metal salts that produce colors. When the salts are heated, tiny particles called electrons absorb the heat and are promoted to higher energy levels where they emit light, or various colors, at different wavelengths.
Violet or blue colors are produced at higher energies that correspond to shorter wavelengths. Conversely, orange and red colors — on the opposite end of the spectrum — are produced at lower energies and correspond to shorter wavelengths.
Compound Interest's color graph of the chemistry of fireworks provides an insight to the elements used to display specific colors:
Why are fireworks so loud?
The loud booms of fireworks heard at ground level are the result of a rapid release of energy into the air, causing the air to expand faster than the speed of sound. This rapid expansion produces a shock wave referred to as a sonic boom.
Fireworks are a class of explosive pyrotechnic devices that date back to seventh century China, where they were invented. They are designed to burn with flames of sparks of many colors — typically red, orange, yellow, green, blue, purple, silver and gold — and are the focal point of many cultural and religious celebrations.