What is the cause for the duration of fireworks?

              For visual effects in fireworks pyrotechnic chemists are not trying to create an explosion, they want to burn the ingredients slowly to make a longer and brighter show. For this to occur, chemists have to use a specific size for the each of the particles of the ingredients. Also the ingredients have to be blended just right to get the right effect.

              To make the burning of the ingredients of the fireworks slower chemists use larger grains of the chemicals to about 250 to 300 microns (its the size of a small grain of sand). Then the ingredients are not mixed very well so that it makes it harder for the fuel and oxidizer to combine and burn. For the even brighter and flashy parts of the fireworks they use even larger grain that are about 1 thousand microms in size. This produces a longer and brighter effect.