Flash powder is a mixture of oxidizer and metallic fuel which burns extremely quickly and if confined will produce a loud report. It is widely used in fireworks and theatrical pyrotechnics, and was once used for flashes in photography.
Different varieties of flash powder are made from different compositions; most common are potassium perchlorate and aluminium powder. Sometimes, sulfur is included in the mixture to increase the sensitivity.
Chemically, flash powder is highly unstable. It is a heat, static, friction, and impact sensitive explosive. It is considered to be one of the most volatile pyrotechnic compositions.
Flash powders, specifically chlorate/perchlorate ones, are very unique in that they produce no gas products (all solid products), which means that they are not explosives by definition. The loud report/explosion heard from salutes and M80s is due to the near instantaneous rise in temperature and pressure within the container, which can exceed 400 times that of standard atmospheric pressure. They also display the unique property of switching from very rapid burning (deflagration) to detonation and thus the very loud sharp sound. Detonation produces pressure waves of some 25,000 feet per second as compared to the common burn rate of 25 feet per second displayed by gun powder.
A larger quantity of flash powder will produce a report if placed loosely in a tube with a diameter between 1/2 and 1 inch.
Types of flash powder
There are many types of flash powder, these are for reasons such as: colours, speed, stability, availability. For example if you want a red flame a suitable oxidizer would be Strontium nitrate, and if you want a faster burning powder, use Magnesium metal powder instead of Aluminum. Mesh size is also a factor, as the finer the mesh, the faster it will burn.
Skylighter Fireworks Tips suggests diapering normally made Al+KCLO4-flashpowder and double-base 'Bullseye'-brand smokeless powder half and half together to get brighter, louder flashpowder called D4F-powder. The Bullseye smokeless powder has a goodly amount of nitroglycerine in it.