Firework chemistry

Firework colours:

There are two main mechanisms of color production in fireworks, incandescence and luminescence. 

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. Metals, such as aluminium, magnesium and titanium, burn very brightly and are useful for increasing the temperature of the firework. 

Luminescence is light produced using energy sources other than heat. Luminescence 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.

The following table illustrates the compounds required to produce specific coloured fireworks.

Colour	Compound	Wavelength of Light
Red	Strontium Salts & Lithium Salts Li2CO3 SrCO3	600-646nm
Orange	Calcium Salts CaCl2 CaSO4.2H2O	591-603nm
Gold	Incandescence of Iron or Charcoal	590nm
Yellow	Sodium Compounds NaNO3 Na3AlF6	589nm
Electric White	White Hot Metal BaO	564-576nm
Green	Barium compounds with Chlorine BaCl+	511-533nm
Blue	Copper Compounds and Chlorine Cu3As2O3Cu(C2H3O2)2	460-530nm
Purple	Mixture of Strontium (red) and Copper (blue) compounds	432-456nm
Silver	Burning aluminium, titanium or magnesium powder.	412nm

An interesting fact

It has taken pyrotechnicians years to solve the problems which lie behind coloured firework production. They have mostly succeeded except for the production of the ocean and forest green coloured firework.

A combination of green and blue coloured emmiters (such as BaCl and CuCl) is the obvious choice. However BaCl and CuCl emissions are difficult to obtain. Hence, the quest for the forest and ocean green coloured fireworks still continues.

More about fireworks:

Fireworks are usually made out of the following items; an oxidizing agent, a reducing agent, a coloring agent, binders and regulators. 

Oxidizing agent - These produce oxygen to burn the mixture. Oxidizers are usually nitrates, chlorates or perchlorates. The common oxidizers are nitrates, which are made up of a metal ion and the nitrate ion. An example of such a chemical equation: . Hence, oxygen is produced.

Reducing Agents - burn the oxygen produced by the oxidizers to produce hot gasses. Two examples of reducing agents are sulfur and charcoal(carbon). These react with the oxygen to form sulfur dioxide and carbon dioxide respectively. 

Keywords explained:

1) Incandescence - light produced from heat.

2) Luminescence - light produced using energy sources other than heat. 

3) Pyrotechnicians - an individual responsible for the safe storage, handling, and functioning of pyrotechnics (the science of materials capable of undergoing self-contained and self-sustained exothermic chemical reactions for the production of heat, light, gas, smoke and/or sound) and pyrotechnic devices.

4) Perchlorates - salts derived from perchloric acid (HClO₄). They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders.