Each year, thousands of firework shows illuminate the skies all across the world. These bombs bursting in the air come in a huge variety of different sizes, shapes and colours. Generating these different effects requires chemical knowledge of the properties of different metals because metal compounds are the key to producing a colourful and entertaining fireworks display.
Red and Yellow
To produce a red explosion, fireworks designers need to produce a flame that emits light at approximately 652 nanometres. Compounds containing strontium and lithium burn close to this wavelength and are used in different proportions to produce red effects. Yellow flames require metals that emit at slightly shorter wavelengths, between 610 and 621 nanometres. Sodium compounds, such as sodium chloride and sodium carbonate, are used to produce yellow effects.
Green and Blue
Green colours are produced by flames emitting light in the range of 590 nanometres. Fireworks designers typically use compounds containing barium and chlorine to produce a green explosion. Blue colours require an even shorter wavelength of light, in the range of 500 to 535 nanometres. Copper is the primary metal used to produce a blue flame. Like barium, the copper compounds that are used usually contain chlorine atoms: copper chloride (CuCl), for example.
White and Silver
White and silver explosions are generated by igniting metals that burn white-hot. Magnesium, in particular, produces a very bright white colour when burnt. It is sometimes added to other fireworks also to increase the overall brightness of a burst or to add white sparks. Titanium and aluminium also burn with a white-hot colour. They are used to produce white and silver colours as well. Aluminium is commonly found in sparklers.
Shapes and Effects
In addition to making colours, metals can produce other effects to enhance a fireworks display. Antimony, for example, is used to produce a shimmering or glittering effect, while zinc creates large amounts of smoke. Colour compounds, along with black powder and various binding agents, are typically packed into small lumps of dough-like material called "stars." These stars are arranged inside the firework shell. Fireworks manufacturers create different bursting shapes by arranging the stars in particular patterns, varying the metals that each star contains.