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.