Flash powder is used in many exploding fireworks, it's in firecrackers, M80's, aerial salutes and many other devices. It is much more powerful than black powder, as well as being significantly more sensitive to shock, sparks, static and friction. One interesting property of flash is that good quality flash (using the standard flash composition) will explode (not just flare up like black powder or similar powders) loose in a pile with only 30-50 grams. For black powder the amount required for an uncontained explosion is around 500 pounds according to some sources, sadly IÔø‡ve never had enough to test thatÔø‡
There are many different recipes for flash (see the Composition Database), but the standard mix is 70/30 (by weight) potassium perchlorate/aluminum flake powder. The finer the powder, the better the final product. This is because of an important principle called surface area. Think of it as lighting paper with a match. Lighting the corner of a flat sheet of paper is much easier than lighting the middle, or, in the case of atomized aluminum (spherical, not good for flash powder) lighting a tightly wadded ball of paper. The finest aluminum is 2-3 micron, extremely good for flash powder. The aluminum often causes trouble because people buy the wrong kind. The best aluminum powder is called Ôø‡dark flake aluminumÔø‡, often 600 mesh powder. Larger particle sizes, such as 400 mesh, will also work, but not as well, the finer the better.
Before attempting to make flash, read this! (not written by me)
Potassium perchlorate (KClO4, sometimes just called Ôø‡percÔø‡)
Aluminum flake powder (as fine as possible)
Pyrotechnic compositions are always by weight, so you need a good scale. If you are new to flash I suggest making 10g, any more is risky and any less itÔø‡s easy to get your ratios off, especially if you donÔø‡t have a great scale. Ideally your scale will have 0.1g accuracy. Once you get some experience you can make larger batches, I personally never make more than 100g at a time. Be sure to wear proper safety equipment such as eye protection and gloves, spraying yourself with anti-static spray (available at grocery stores in the laundry section) is also a good idea.
Chemicals and scale:
First weight out 7g of KClO4 on a piece of newspaper (newspaper is used to reduce messes and contamination). If there are any lumps crush them with a plastic spoon or if it is very clumpy you can put it through a sieve. Set this aside.
Weighing the perc:
Next weight out 3g of your Al powder.
Weighing the Al:
The two powders are then poured onto a larger sheet of newspaper. As you can see in the picture the density of each is very different, you cannot try to measure by volume and say Ôø‡IÔø‡ll just use 7 scoops of perc and 3 of AlÔø‡ because itÔø‡ll be way off.
Ready for mixing:
The flash is mixed using the Ôø‡diaper methodÔø‡ where the corners of the paper are lifted up to make the powder fall onto itself. This is the safest method of mixing flash because it makes almost no friction. An alternate method is shaking it in a bag but donÔø‡t worry about that if you are a beginner. Diaper mixing takes a little practice to do it properly but it quickly becomes very easy.
When well mixed, the flash should have a uniform gray color like the picture below. The color of your flash will depend on your Al powder, so it could be lighter or darker than this.
Good flash will burn very quickly-almost instantly-and make a Ôø‡whoomph!Ôø‡ noise and puff of smoke. Below is 1g of loose flashpowder burning. The frames are 3 consecutive frames from my camera, so you can tell it burnt very quickly.
1g loose flash:
1g loose flash burning: