Fireworks use black powder, also known as gunpowder. They are classed as low explosives in contrast to the infinitely more powerful high explosives such as TNT and dynamite.

In pyrotechnics an oxidizer and a fuel react together to produce light.

Bombs and mortars
The central tool in fireworks is the shell or "bomb". A bomb is usually round or cylindrical in shape and is covered with a casing of cardboard and/or plastic and twine - with a lift-charge beneath it made from black powder.

The bomb is inserted into a mortar (a gun-like cylinder with a bottom plug) made of cardboard, plastic or steel for the larger bombs. The mortar serves as the bomb's launching pad. The mortars and bombs are wired to a central firing booth, from which the bombs' lift-charges are ignited electrically throughout the show.

When the lift-charge explodes, the bomb shoots out of the mortar up into the air. In the core of the shell is another exploding charge with a delay fuse. When the shell is fired from the mortar, it in turn ignites the delay fuse, which is cut to a length that will set off the explosive charge inside the shell at the right height and the right time.

The explosive charge at the centre of the bomb is made of black powder or flash powder (composed of potassium perchlorate, aluminum powder, and/or magnesium which, upon ignition, creates a violent explosion combined with a flash). The explosion sends the burning stars out in a particular pattern determined by the way the shell was packed by the bomb maker - creating the colourful effect the crowd sees.

Stars
Each bomb is very carefully constructed in a fireworks' factory. A chemist produces the powders and presses or rolls them into pellets called stars which are spherical, cylindrical or cube-shaped.

When lit, the stars produce a brilliant ball of fire. They are made with oxygen-rich components such as strontium nitrate, potassium perchlorate, potassium nitrate and potassium chlorate. The star contains both oxidizer and fuel. When the oxidizer burns with the fuel made of charcoal, titanium powder and aluminum powder or other metal or carbon-based mixtures, the reaction to the burning of both oxidizer and fuel creates the effect of colour.

The shell maker assembles the stars within the shell casing, in a careful configuration that determines the height at which the star will be expelled and so as to produce any desired effects (such as the star being expelled in a particular shape such as a heart or circle).

The formulas
There are only about 100 top fireworks manufacturers in the world. Each company's formulas are closely-guarded secrets. The chemical and powder recipes are often handed down through generations of families. The colour, animation, sound and flight pattern of each shell depends on its design and on the blend of its chemical ingredients.

The colors
In fireworks there are six common colors, made by adding a specific chemical compound.

• White is produced by magnesium or aluminum or titanium
• Yellow by sodium salts
• Red by strontium nitrate
• Green by barium nitrate or chlorate
• Blue by copper compounds
• Orange/amber by charcoal or other carbon or iron compounds

Deep blue and purple are the most difficult fireworks colors to create because they have a very narrow band on the colour spectrum, requiring the chemical reaction to be absolutely perfect. In fact, the creation of a deep blue flame remains one of the great unsolved challenges to pyrotechnicians. However, blue and green are considered the most dangerous colors to produce.