Fireworks Chemicals – The Chemistry of Fireworks

From basic noisemakers comprised of merely a fuse and a small amount of black powder wrapped in paper to the massive professional fireworks which travel hundreds of feet into the air and often involve multiple complex stages which can take weeks if not months to assemble, the chemistry of fireworks and their intense displays of sound and light is a wonder shared by both small children and adults alike.  In general though what exactly is the chemistry in fireworks – How does a firework work and what chemicals cause are responsible for a fireworks color?

Chemistry of Fireworks

Most common fireworks that can be purchased from the shops and tents that you generally see around the Fourth of July still rely on black powder to launch and explode their aerial shells.  They use fewer stages than professional shells but are still designed to precisely control the effects created at different times throughout the fireworks life.  The main method behind an aerial fireworks propulsion is the rapid release of carbon dioxide and nitrogen focused through a small hole or down a path which creates a downward force through the use of rapid decomposition.  This opposing reaction propels the projectile into the air before the final effects of instantaneous detonation are triggered from the heat or flame reaching the additional black powder, oxidizers and colorants that are combined in the rest of the shell.

Careful calculations are made to insure that the fuel used to lift the projectile in the air expires just as the secondary materials which cause the intended effect is triggered, this insures that the firework explodes at the proper time and not to early or late when it could be close to the ground.

What Causes a Fireworks Color?

Fireworks generally require a fuel source, oxygen producer, binder to maintain the placement of ingredients, and coloring material to produce the intended incandescence (light produced form heat) and luminescence (light produced from means other than heat).

To form incandescence colors typical ingredients include aluminum, magnesium, and titanium due to how bright they burn.  Their burn temperature affects the color given off by the substance – hotter burns produce a whiter light and cooler temperatures produce light traveling down visible spectrum to other colors including yellow, orange, red, and finally infrared light.

Luminescence burns often rely on substances which are less stable and require additional ingredients to stabilize the compound.  These colors are often not as bright as incandescent colors due to some combinations tendency to become too unstable at high temperatures to last, so the heat must be properly controlled.

To create a good firework you need very pure ingredients as even impurities at small levels can alter or overwhelm the intended colors.   This not only affects the light produced as impure ingredients can lead to fireworks that produce too much smoke which can mask the light and other effects.

Standard Black Powder:

75% Potassium Nitrate (Oxidizer)

15% Carbon – Generally Charcoal or Sugar (Fuel)

10% Sulfer (Moderates Reaction)

Chemicals that Produce a Fireworks Color:

Red Strontium salts, lithium saltsLithium carbonate, Li2CO3 = redStrontium carbonate, SrCO3 = bright red
Orange Calcium saltsCalcium chloride, CaCl2Calcium sulfate, CaSO4·xH2O, where x = 0,2,3,5
Gold Incandescence of iron (with carbon), charcoal, or lampblack
Yellow Sodium saltsSodium chloride, NACISodium nitrate, NaNO3Cryolite, Na3AlF6
Electric White White-hot metal, such as magnesium or aluminumBarium oxide, BaO
Green Barium compounds + chlorine producer = greenBarium chloride, BaCl2 = bright green
Blue Copper compounds + chlorine producerCopper acetoarsenite (Paris Green), Cu3As2O3Cu(C2H3O2)2 = blueCopper (I) chloride, CuCl = turquoise blue
Purple Mixture of strontium (red) and copper (blue) compounds
Silver Burning aluminum, titanium, or magnesium powder or flakes

 

Interesting Points on the Chemistry of Fireworks:

  • Some professional fireworks can be set off just from an impact or changes to their environment.  Because of this they are often stored in highly controlled environments.
  • It is thought that fireworks were originally invented in China.  At that time the gunpowder was incased in bamboo shoots which exploded when lit. These fireworks were traditionally used do to the belief that the loud bang produced would scare away evil spirits.
  • Some professional fireworks now use compressed air as a propulsion system and electronic timers as detonators in order to create more elaborate shows through better control of the blasts timing.
  • If you start counting when you see the firework and stop counting when you hear it, then divide the number of seconds counted by 3 you will get the roughly the distance in kilometers away that the firework blast was.  This is because the speed of light is roughly 300 million meters per second where the speed of sound is 340 meters per second.

For sourcing or more information visit:

NOVA website – http://www.pbs.org/wgbh/nova/fireworks/anat_nf.html