Only a few days ago it was Guy Fawkes night in England and in a month’s time it is New Year’s Eve. People will be rushing to the fireworks shops and will be getting ready to launch thousands of pounds of fireworks into the sky. In light of these events I decided to write a short blog about why fireworks display their characteristic colours.
To understand why these colours are displayed we need to know of what chemicals are used in the fireworks. For the reaction we need oxygen, heat and fuel and something to give the reactions colour. These all come from the chemicals packed inside the fireworks.
A lot of physics and chemistry go into the making of fireworks. The different colours all come from the excitation of the atoms. For example copper burns green, this is because the electrons of copper get “heated” into an excited state and this excited state is not stable. The atom tries to lose that energy by lowering the excited state of the electron back to a normal state by releasing a photon. This is just like the GFP protein in the first blogpost.
By using different elements in different reactions we can vary the colour.
I have added a list of metal and chemical compounds that are used in fireworks. I have also added what their roles are in the reactions.
Aluminium – Aluminium is used to produce silver and white flames and sparks. It is a common component of sparklers.
Antimony – Is used to create firework glitter effects.
Barium – Is used to create green colours in fireworks and it can also help stabilize other volatile elements.
Calcium – Is used to deepen firework colours. Calcium salts produce orange fireworks.
Carbon – One of the main components of black powder, used as a propellant in fireworks.
Chlorine – An important component of many oxidizers (= provides oxygen) in fireworks. The metal salts that provide the colour often contain chlorine.
Copper – Copper compounds produce blue (Cu+) or green (Cu2+) colours in fireworks. (Copper I is Cu+ with a single positive charge and Copper II is Cu2+ with two positive charges)
Iron – Is used to produce sparks. The heat of the metal determines the colour of the sparks. White-yellow at about 1300 °C and red-yellow at around 1000 °C.
Lithium – A metal that is used to impart a red color to fireworks.
Magnesium – Burns a very bright white, so it is used to add white sparks or improve the overall brilliance of a firework.
Potassium – Helps to oxidize firework mixtures. Potassium nitrate, potassium chlorate, and potassium perchlorate are all important oxidizers.
Sodium – Imparts a gold or yellow colour to fireworks. However, this may be so bright that it masks less intense colours.
Sulphur – A component of black powder. It is found in a firework’s propellant/fuel.
Strontium – Provides a red colour to fireworks. Compounds of strontium are also important in stabilizing the mixtures.
Titanium – Can be burned as powder or flakes to produce silver sparks.
Zinc – Is used to create smoke effects for fireworks and other pyrotechnic devices.
“Coloured Flames – Periodic Table of Videos”
Anne Marie Helmenstine, Ph.D., About.com Guide on metals in fireworks
Atkins, Jones. (2010) Chemical Principles – Fifth edition p35
http://www.eauclairewi.gov/recreation-home-page/recreation-information/fourth-of-july-celebration (For the featured image)