so these mixtures are generally considered too unstable to be stored and must be mixed immediately before use. Antimony trisulfide may be used as an alternative, and is more stable in storage. Potassium nitrate, aluminium and sulfur This composition, usually in a ratio of 5 parts potassium nitrate, to 3 parts aluminum powder, to 2 parts sulfur, is especially popular with hobbyists. It is not very quick-burning unless exceptionally fine ingredients are used. Although it incorporates sulfur, it is in fact fairly stable, sustaining multiple hits from a hammer onto a hard surface. Adding 2% of its weight with boric acid is reputed to significantly increase stability and shelf life, through resistance to dampening through ambient humidity. Other ratios such as 6 KNO3/3 Al/2 S and 5 KNO3/2 Al/3 S also exist and work. All ratios have similar burn times and strength, although 5 KNO3/3 Al/2 S seems to be dominant. 2 KNO3 + 4 Al + S → K2S + N2 + 2 Al2O3 The composition is approximately 59% KNO3 : 31.6% Al : 9.4% S by weight for the reactants of the above stoichiometrically balanced equation. For best results, "German Dark" aluminum should be used, with air float sulfur, and finely ball-milled pure potassium nitrate. The finished mixture should never be ball milled together. Aluminium and perchlorate Aluminium powder and potassium perchlorate are the only two components of the pyrotechnic industry standard flash powder. It provides a great balance of stability and power, and is the composition used in most commercial exploding fireworks. aka A B mixture The balanced equation for the reaction is: 3 KClO4 + 8 Al → 3 KCl + 4 Al2O3 The stoichiometric ratio is 34.2% aluminum and 65.8% perchlorate by mass. A ratio of seven parts potassium perchlorate to three parts dark pyro aluminium is the composition used by most pyrotechnicians. For best results, the aluminium powder should be "Dark Pyro" grade, with a flake particle shape, and a particle size of fewer than 10 micrometres. The KClO4 should be in powder form, free from clumps. It can be sieved through a screen, if necessary, to remove any clumps prior to use. The particle size of the perchlorate is not as critical as that of the aluminium component, as much less energy is required to decompose the KClO4 than is needed to melt the aluminium into the liquid state required for the reaction.