A splendid fireworks display can be the highlight of any festival. It’s a feast for the senses. And lately, it’s not just been festivals, even small celebrations, such as graduations or sporting events are a popular time for this colorful artistry. Long before a show begins, these fireworks have to be designed. At what height should they explode? How broad should the burst be? What colours or hues — should each burst deliver? And how do they even burst? — explains Michael Pollastri, associate professor and chair of the Chemistry department at Northeastern University.
“An explosion is more or less a very fast and intense burning event. In order to accomplish that, metal salts are mixed with chemicals (oxidising agents) that cause a very rapid oxidation reaction to occur. This reaction is very fast and exothermic, which means it gives off energy as heat—and anytime you have a very fast and hot reaction, you get an explosion. This launches the fireworks into the sky and the heat from this explosion is what provides the energy to create the colours,” explains Pollastri.
Fireworks were invented in China more than 2,000 years ago and have come a long way to the high tech versions of the now that use special metals and chemicals that when heated get excited to a higher energy state, and when the atoms relax back to their more stable “ground” state, they emit colours. The wavelength (or colour) of light that’s emitted when these atoms relax are characteristic of specific atoms: strontium glows red, sodium burns orange, copper burns green, etc. Other colors can be made by mixing these metal salts in the fireworks, which is called “painting” in the fireworks trade.
“Blue fireworks are particularly difficult to create because the copper salt needs a very precise temperature to be excited to the energy state that emits blue light. If it burns too hot or too cool, the colour gets washed out to a lighter blue hue,” Pollastri explains.