Simple fireworks consist of a paper tube filled with stars and black powder. Stars come in all shapes and sizes, but you can imagine a simple star as something like a sparkler formed into a ball the size of a pea or a 5p. This is all lifted up in to the sky by a lifting charge or propellant. The stars are poured into the tube and then surrounded by black powder or flash powder. When the fuse burns into the shell, it ignites the lifting charge which launches the firework skywards. Once the propellant has burnt through the rocket is still climbing so a slower burning powser, called the delay charge starts burning. This then ignites the bursting charge, causing the shell to explode. The explosion ignites the outside of the stars, which begin to burn with bright showers of sparks. Since the explosion throws the stars in all directions, you get the huge sphere of sparkling light that is so familiar at fireworks displays.
What makes fireworks different colours
The different colours in fireworks come from the chemicals added to the stars.
Red strontium salts, lithium salts, lithium carbonate, Li2CO3 = red, strontium carbonate, SrCO3 = bright red
Orange calcium salts, calcium chloride, CaCl2, calcium sulfate, CaSO4·xH2O, where x = 0,2,3,5
Gold incandescence of iron (with carbon), charcoal, or lampblack
Yellow sodium compounds, sodium nitrate, NaNO3, cryolite, Na3AlF6
Electric White white-hot metal, such as magnesium or aluminum, barium oxide, BaO
Green barium compounds + chlorine producer, barium chloride, BaCl+ = bright green
Blue copper compounds + chlorine producer, copper acetoarsenite (Paris Green), Cu3As2O3Cu(C2H3O2)2 = blue, copper (I) chloride, CuCl = turquoise blue
Purple mixture of strontium (red) and copper (blue) compounds
Silver burning aluminum, titanium, or magnesium powder or flakes
Pure colours require good quality ingredients. Colours can be distorted easily, for example, minute amounts of the yellow producing salt, sodium is sufficient to overpower or alter other colors. Careful formulation is required so that the smoke or residue does not mask the color. With fireworks, as with other things, cost often relates to quality. Skill of the manufacturer and date the firework was produced greatly affect the final display.
So what is the stick for on a rocket?
Rockets are powerful things, there is a huge amount of energy released when the firework is launched. The stick on a rocket makes the whole firework more stable. The stick changes the center of mass (balance) of the firework, making sure that the thrust lifting the rocket is always above the rocket’s center of mass, thus keeping it stable. Airbourne fireworks without sticks are called missiles or mortars, these fireworks do not need as stick as they are launched from a tube. The tube ensures that the fireworks thrust is all directed towards launching the firework upwards.
More questions about fireworks? See our firework FAQ.