Pyrotechnicians, or fireworks artists, were being formally trained to light up the night sky with flashes of near-white light since before the 15th century. Today we see yellow, orange, red, blue and green, but this was not always the case. Italy is credited for bestowing variety to the ubiquitously seen oranges and faint gold illuminations after forming colors in their fireworks displays in the 1830’s. This was the beginning of transforming fireworks from just a sonic boom to a spectacularly vivid light show.

Basically

The myriad of colors formed by fireworks is due to chemical reactions and temperature. You probably met a little boy named Roy G. Biv in the 6th grade who resides between 400 to 700 nanometers (nm): visible light (Red, Orange, Yellow, Green, Blue, Indigo, Violet).

Not-so-basically

Solid and gas phase materials called light emitters allow fireworks to emit an array of colors through a series of oxidation-reduction reactions.

Solid state emitters make up black body radiation which absorb all electromagnetic radiation in its surrounding and emits it at the same rate to maintain thermal equilibrium. Black body radiation at 480°C is seen as a faint red glow, but increasing the temperature to 930°C gives a bright orange. Going up to 1300°C results in a yellowish white.

Achieving pigments beyond yellows and oranges needs atoms and molecules, referred to as gas phase emitters. Atoms absorb and release energy as light based on their electron states. Electrons get excited and that’s when we see the colors.

Low energy = long wavelength (nm) = red and orange.

High energy = short wavelength (nm) = blue and violet.

Emissions from strontium chloride (SrCl) and strontium hydroxide (SrOH) result in lovely deep reds in the 617 to 647nm wavelength range. Copper chloride (CuCl) makes an intense blue within 403-456nm. Significant quantities of emitters are packed into stars with other ingredients to obtain good colors.

Peak illumination emerges when temperatures are reached and held just right. Extremely high temperatures are needed for colors like blue- similar to that of an 8,726.85°C celestial star. This amount of heat is crazy to achieve for an earth-based fireworks show, so chemical emitters are used to ease that restraint. Powdered magnesium and aluminum create elevated temperatures and intensify the light. However, CuCl will be destroyed with too high heat, so blue stars are not very bright.

So maybe you will not remember that we need strontium to create that lustful red seen on the 4th of July. Nevertheless, take into account that your expelled ooh’s and aah’s over the gorgeous fireworks is a thrill provoked by a delicate combination of excited electrons and fiery temperatures. Like a supernova in outer space.