Name: 7:3 Flash
| percent | parts | component |
|---|---|---|
| 70.00% | 7 | Potassium Perchlorate |
| 30.00% | 3 | Aluminium (-325 mesh, dark flake) |
Screen and ball mill potassium perchlorate as fine as possible. Mix using diaper method only. Do not screen once the Aluminium has been added.
May detonate unconfined the critical mass is quite small and may be as little as 5 g or less with reactive Aluminiums. Make as small a batch as possible, less than 10 g is strongly recommended, 1 g preferred. Make and use immediately, do not store loose flash.
The Aluminium is very critical to the composition effectiveness, dark pyro flakes designed for flash use are optimal. Bright/greasy or coarse flakes will burn fairly slow and are quite effective in large lances for waterfall effects or as bright cores for rolled stars but will make disappointing report charges.
Atomised Aluminiums will be very hard to ignite and will produce an essentially useless composition. Any Aluminium over -325 mesh will be useful for stars and falls only.
Flash is based on stoichiometric reaction:
3(KClO4) + 8(Al) => 3(KCl) + 4(Al2O3)
Which derives a composition (2 significant percentage figures):
66 Potassium Perchlorate
34 Aluminium
The other popular flash ratio is 2:1 which is very near stoichiometric. The 7:3 ratio is over-oxidised for speed. Either of these "round number" ratios work for all practical purposes identically.
Note that the reaction is essentially gasless. In practice of course some gas is produced and air within and surrounding the flash is strongly heated and expands enormously. The practice of under-filling salutes or using bulking agents to enhance the bang may function more due to supply of a larger quantity of working fluid than that provided by interstitial air, rather than enhanced flame-front propagation. No doubt both effects are important.