Incandescence and Luminescence

Creating firework colors is a complex endeavor, requiring considerable art and application of physical science. Excluding propellants or special effects, the points of light ejected from fireworks, termed 'stars', generally require an oxygen-producer, fuel, binder (to keep everything where it needs to be), and color producer. There are two main mechanisms of color production in fireworks, incandescence and luminescence.

Incandescence

Incandescence is light produced from heat. Heat causes a substance to become hot and glow, initially emitting infrared, then red, orange, yellow, and white light as it becomes increasingly hotter. When the temperature of a firework is controlled, the glow of components, such as charcoal, can be manipulated to be the desired color (temperature) at the proper time. Metals, such as aluminum, magnesium, and titanium, burn very brightly and are useful for increasing the temperature of the firework.

Luminescence

Luminescence is light produced using energy sources other than heat. Sometimes luminescence is called 'cold light', because it can occur at room temperature and cooler temperatures. To produce luminescence, energy is absorbed by an electron of an atom or molecule, causing it to become excited, but unstable. When the electron returns to a lower energy state the energy is released in the form of a photon (light). The energy of the photon determines its wavelength or color.

Sometimes the salts needed to produce the desired color are unstable. Barium chloride (green) is unstable at room temperatures, so barium must be combined with a more stable compound (e.g., chlorinated rubber). In this case, the chlorine is released in the heat of the initial pyrotechnic detonation, to then form barium chloride and produce the green color. Copper chloride (blue), on the other hand, is unstable at high temperatures, so the firework cannot get too hot, yet must be bright enough to be seen.

Materials Used to Make Colors in Fireworks

Red: lithium carbonate, Li₂CO₃ = red
strontium carbonate, SrCO₃ = bright red

Orange: calcium chloride, CaCl₂
calcium sulfate, CaSO₄· xH₂O, where x = 0,2,3,5

Gold: incandescence of iron (with carbon), charcoal, or lampblack

Yellow: sodium nitrate, NaNO₃
cryolite, Na₃AlF₆

Electric White: white-hot metal, such as magnesium or aluminum
barium oxide, BaO

Green: BaCl₂ = bright green

Blue: copper acetoarsenite (Paris Green), Cu_3sAs₂O₃Cu(C₂H₃O₂)₂ = blue
copper (I) chloride, CuCl = turquoise blue

Purple: mixture of strontium (red) and copper (blue) compounds

Silver: burning aluminum, titanium, or magnesium powder or flakes