The Chemistry of Firework Colors

Fireworks are a traditional part of many celebrations, including Independence Day. There is a lot of physics and chemistry involved in making fireworks. Their colors come from the different temperatures of hot, glowing metals and from the light emitted by burning chemical compounds. Chemical reactions propel them and burst them into special shapes. Here's an element-by-element look at what is involved in your average firework.

Components in Fireworks

Aluminum: Aluminum is used to produce silver and white flames and sparks. It is a common component of sparklers.

Antimony: Antimony is used to create firework glitter effects.

Barium: Barium is used to create green colors in fireworks, and it can also help stabilize other volatile elements.

Calcium: Calcium is used to deepen firework colors. Calcium salts produce orange fireworks.

Carbon: Carbon is one of the main components of black powder, which is used as a propellant in fireworks. Carbon provides the fuel for a firework. Common forms include carbon black, sugar, or starch.

Chlorine: Chlorine is an important component of many oxidizers in fireworks. Several of the metal salts that produce colors contain chlorine.

Copper: Copper compounds produce blue colors in fireworks.

Iron: Iron is used to produce sparks. The heat of the metal determines the color of the sparks.

Lithium: Lithium is a metal that is used to impart a red color to fireworks. Lithium carbonate, in particular, is a common colorant.

Magnesium: Magnesium burns a very bright white, so it is used to add white sparks or improve the overall brilliance of a firework.

Oxygen: Fireworks include oxidizers, which are substances that produce oxygen in order for burning to occur. The oxidizers are usually nitrates, chlorates, or perchlorates. Sometimes the same substance is used to provide oxygen and color.

Phosphorus: Phosphorus burns spontaneously in air and is also responsible for some glow-in-the-dark effects. It may be a component of a firework's fuel.

Potassium: Potassium helps to oxidize firework mixtures. Potassium nitrate, potassium chlorate, and potassium perchlorate are all important oxidizers.

Sodium: Sodium imparts a gold or yellow color to fireworks, however, the color may be so bright that it masks less intense colors.

Sulfur: Sulfur is a component of black powder. It is found in a firework's propellant/fuel.

Strontium: Strontium salts impart a red color to fireworks. Strontium compounds are also important for stabilizing fireworks mixtures.

Titanium: Titanium metal can be burned as powder or flakes to produce silver sparks.

Zinc: Zinc is used to create smoke effects for fireworks and other pyrotechnic devices.

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. The energy is supplied by the heat of the burning firework. 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.​

In some cases, 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 burning of the pyrotechnic composition, 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.

Quality of Firework Ingredients

Pure colors require pure ingredients. Even trace amounts of sodium impurities (yellow-orange) are sufficient to overpower or alter other colors. A careful formulation is required so that too much smoke or residue doesn't mask the color. With fireworks, as with other things, cost often relates to quality. The skill of the manufacturer and date the firework was produced greatly affect the final display (or lack thereof).

Table of Firework Colorants

Color	Compound
Red	strontium salts, lithium salts lithium carbonate, Li2CO3 = red strontium carbonate, SrCO3 = bright red
Orange	calcium salts calcium chloride, CaCl2 calcium sulfate, CaSO4·xH2O, where x = 0,2,3,5
Gold	incandescence of iron (with carbon), charcoal, or lampblack
Yellow	sodium compounds sodium nitrate, NaNO3 cryolite, Na3AlF6
Electric White	white-hot metal, such as magnesium or aluminum barium oxide, BaO
Green	barium compounds + chlorine producer barium chloride, BaCl+ = bright green
Blue	copper compounds + chlorine producer copper acetoarsenite (Paris Green), Cu3As2O3Cu(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

Sequence of Events

Just packing colorant chemicals into an explosive charge would produce an unsatisfying firework! There's a sequence of events leading to a beautiful, colorful display. Lighting the fuse ignites the lift charge, which propels the firework into the sky. The lift charge can be black powder or one of the modern propellants. This charge burns in a confined space, pushing itself upward as hot gas is forced through a narrow opening.

The fuse continues to burn on a time delay to reach the interior of the shell. The shell is packed with stars that contain packets of metal salts and combustible material. When the fuse reaches the star, the firework is high above the crowd. The star blows apart, forming glowing colors through a combination of incandescent heat and emission luminescence.