This article was taken from the FPGA newsletter after a competition they held at a shoot. The competition was who could make the best blue firework star composition.
I Really Blue It This Time!
By Mark Wilbur
My evening shooting included seven blue firework star compositions for the blue firework star competition. I was quite surprised and greatly pleased to win 1st place with a blue firework star shell I shot. All the blues looked pretty much the same to me, with the exception of Veline's Magnalium Blue. It was a brighter firework star, but it looked washed out compared to the other blue firework stars. In my pursuit for a deep blue firework star I searched the pyro literature for the many published blue pyrotechnic formulas and wrote the pyrotechnic formulas down side by side for comparison. I grouped them by oxidizer first and by coloring agent second. The many pyrotechnic formulas were relatively close in ingredients and percentages. I narrowed the selection to two potassium chlorate (KClO3) mixes, five potassium perchlorate (KClO4) mixes, and two ammonium perchlorate mixes. I wasn’t able to make the ammonium perchlorate mixes in time, so I still have that on my list of "Try These" formulae. The blue firework stars I tried used copper oxide, copper carbonate, or copper oxychloride as the coloring agents.
Some of the published pyrotechnic formulas used copper metal, but I decided against trying them. It seemed that the potassium perchlorate mixes produced the deepest blue. It was one of these that won 1st place in the competition. All of my potassium perchlorate mixtures outscored my potassium chlorate mixes. All of the firework stars were cut firework stars. I primed the potassium perchlorate mixes first with Bleser's #22 Igniter and second with ball-milled pulverone prime. The potassium chlorate mixes were lightly primed with ball-milled pulverone prime. Ignition of each firework star mix seemed very good with these preparations. Priming of ammonium perchlorate firework stars is more involved, and that helped to postpone making these firework star compositions.
I enjoyed exploring and experimenting with these mixes. I find the chemistry of this hobby deeply fascinating. In my pyro reading I learned that the copper chloride (CuCl) molecular species is most desired in the flame envelope to emit the deep blue spectra. In order to achieve this, a good chlorine donor is needed. I have been using dechlorane with good success. Blue must also keep a lower flame temperature than other colors. So a hot fuel like magnalium is not preferred. Some other factors peculiar to blue firework stars figured in my choices for mixes. As promised I will share the winning blue firework star formula.
Wilbur's Winning Blue Pyrotechnic Formula
The mix was moistened with water/alcohol 75/25% and cut into firework stars that should have been put in a six inch shell instead of a four inch shell, since they burned all of the way to the ground. I suspect that 3/8 inch cut firework stars are large enough for a four-inch shell. The potassium perchlorate firework stars were easy to light with the two-step prime and did not seem to burn fiercely. A satisfyingly deep blue firework star was achieved.