Pyrotechnic Chemistry

Before building any pyrotechnics, it is necessary to have at least a basic understanding of the chemistry involved. There are some very complex reactions that take place in fireworks that could take a lifetime to fully reveal, but fortunately it does not take so long to understand the overlaying principles. This video goes through the primary types of chemicals and what part they play in a pyrotechnic composition:

Oxidizers are the chemicals that really make pyrotechnic compositions as spectacular as they are. A fuel such as charcoal can burn using only the oxygen in the air, but as we have all experienced at barbeques, it does not burn quickly enough to look anything like a firework. When an oxidizer is mixed with charcoal however, it provides much more oxygen than is in the air, and will burn away much faster and brighter. Were it not for oxidizers, when a firework is packed full of fuels there would not be enough air left inside for them to burn. Rockets and shells would never leave the ground, and the explosions and effects that are in every display would not be possible.

Potassium nitrate and potassium perchlorate are the most common oxidizers in pyrotechnics. Potassium nitrate is used in combination with the two fuels charcoal and sulfur to make black powder, the most important and oldest composition in all of pyrotechnics. If combined in different measurements, potassium nitrate, charcoal, and sulfur can be used to also create many types of stars, most of which have a bushy orange tail that comes from the powdered charcoal falling away and burning as it floats in the sky. Black powder, if made with the traditional mixture can be used for end burning rockets, and if mixed slightly differently can be used for core burning rockets. More information about those things can be found on my black powder and rocketry pages.

Potassium perchlorate is much different than potassium nitrate. While both chemicals are oxidizers and will provide oxygen for fuels to burn, potassium perchlorate contains a chlorine atom, which is an important chemical for making compositions that have a vivid colored flame. Potassium perchlorate does not produce a very bright color on its own when mixed with a standard fuel like charcoal. It instead can be made to burn various colors with the addition of a coloring agent.

Coloring agents are usually metal salts or oxides, or they may even be an oxidizer of their own (such as strontium nitrate for red, or barium nitrate for green). To produce a colored flame using potassium perchlorate, a coloring agent is added, in addition to a fuel such as charcoal, aluminum, or a magnesium/aluminum alloy known as magnalium. When the potassium perchlorate burns away with the fuel, the coloring agent is also heated in the reaction and causes the flame to be tinted whatever color that particular coloring agent produces. The common chemicals that are used for coloring are oxides, chlorides, carbonates, or nitrates of the following:

• Strontium (red)
• Barium (green)
• Copper (blue)
• Sodium (yellow)
• Calcium (orange)

Some salts of those metals are not used in fireworks even though they would probably make a great color. The reason several of the salts cannot be used is because they are hygroscopic, which means they absorb water out of the air – some to the point that they become wet or even turn into a puddle if left in an open container. That would obviously ruin a composition if that much moisture were sucked into it. Some examples of hygroscopic salts include the chlorides and nitrates of sodium, copper, and calcium. Sodium oxalate, copper oxide, and calcium carbonate are commonly used to color stars in place of hygroscopic compounds.

The last primary type of chemical used in most compositions is a binder. As is stated in the above video, a binder is a glue that is used to hold stars or granules of composition together. Some binders, such as dextrin or soluble glutinous rice starch (SGRS) are water soluble, and some such as parlon or red gum are soluble in acetone or alcohol. Water soluble binders are cheap and good for glitter or charcoal based effects but take more time to dry than other binders. Some binders such as parlon also double as a chlorine donor, which adds to the vividness of color stars. Typically a binder only makes up 5% or less of a pyrotechnic composition.

Once these basic components and their place in a pyrotechnic reaction is understood, the effects created by fireworks can be refined down to the finest of detail. It is not until then that true pyrotechnic masterpieces can be created, such as this: