Canada Day was Friday, July 1, 2016, and Monday, July 4 is Independence Day – usually called Fourth of July – in the U.S. So it’s fireworks season in North America, and red, orange, yellow, green, blue and purple colors are exploding into our night skies. The beautiful colors in fireworks – so good at stirring our emotions – are pure chemistry, created by the use of metal salts.
Metal salts commonly used in firework displays include: strontium carbonate (red fireworks), calcium chloride (orange fireworks), sodium nitrate (yellow fireworks), barium chloride (green fireworks) and copper chloride (blue fireworks). Purple fireworks are typically produced by use of a mixture of strontium (red) and copper (blue) compounds.
The metal salts are packed into a firework as pea- to plum-sized pellets called “stars.”
After a firework is ignited, a lift charge propels it into the sky. That’s just explosive black powder in a confined space that, when lit, causes a fast increase of heat and gas that can send a firework as high as 1,000 feet (300 meters) into the air.
Meanwhile, a time-delay fuse burns slowly into the interior of the firework shell. After about 5 seconds, as the shell is soaring overhead, the fuse kindles a charge that reaches the core of the firework, explodes and ignites the stars that contain the metal salts.
Voila! A beautiful and colorful fireworks display.
By the way, the people who create fireworks are precise craftsmen. It’s a complex process, and even one thing being off — too much black powder, stars that aren’t aligned correctly or a trigger that fires too soon or too late — can cause everything else to go wrong.
Bottom line: The red, orange, yellow, green, blue and purple colors exploding in the night sky during a pyrotechnic festival are created by the use of metal salts.
Deanna Conners is an Environmental Scientist who holds a Ph.D. in Toxicology and an M.S. in Environmental Studies. Her interest in toxicology stems from having grown up near the Love Canal Superfund Site in New York. Her current work is to provide high-quality scientific information to the public and decision-makers and to help build cross-disciplinary partnerships that help solve environmental problems. She writes about Earth science and nature conservation for EarthSky.