How To Make Dragon Eggs Crackling Stars Cheaper With Bismuth Subcarbonate
Dragon Eggs: those popular crackle firework stars that so many people love and so many are tired of. Crackle firework stars or dragon eggs were traditionally made with formulas containing toxic lead tetraoxide. Later compounds were developed utilizing non-toxic, but expensive bismuth trioxide. I am told that most Chinese dragon eggs use copper oxide. But somewhere in the dank recesses of my memory, I ran across bismuth subcarbonate dragon eggs. So, when I found some surplus bismuth subcarbonate a couple of years ago, I snatched some up, but never could find the formula for making dragon eggs firework stars with it.
But along comes an email from one of my customers, et voila! He sends me his bismuth subcarbonate firework star experiments. What follows is a strung together conversation he and I had over several emails. Iíll leave it to you to extract from it what you need. But the bottom line, this is a relatively cheap, non-toxic way to make dragon eggs firework stars. And I promptly snagged a good supply of bismuth subcarbonate, which is about half the price of bismuth trioxide. Hereís what he wrote, edited down slightly.
"That bismuth subcarbonate works pretty well to make crackle firework stars. I also like the fact that itís a lightweight powder as opposed to the dense powder that bismuth trioxide is. I've tried a formula of 90% Bismuth Subcarbonate, 10% Magnalium (200 mesh) and 10% black copper oxide. I'm going to try one of the formulas that use a lot less bismuth subcarbonate (75% bismuth subcarbonate, 15% Magnalium, 10% black copper oxide). I'll let you know if it works better or worse."
I asked him to tell me more. He wrote: "As I mentioned earlier, I've tried a 90-10-10 mix of Bismuth Subcarbonate, MgAl 200 mesh, Black Copper Oxide. I haven't primed anything yet, but have lighted several of the little approximately 2mm firework stars on the ground with a torch-style butane lighter. Boy do those things make a racket for such small chunks of firework star composition (about the size of the grains of soft pretzel salt, if even that big). I showed my brother the little firework stars before lighting, and he was absolutely amazed you could get that much sound out of such tiny firework stars. These firework stars were just grated through regular aluminum window screen, which is about 10 mesh. When you take the thickness of the wires into account, you wind-up with almost exactly 2mm firework stars, though you'll probably wind up with a mix of sizes between 1.5 and 2mm.
I've now tried a mix of 75-15-10 and quite frankly, I don't see much, if any difference. Again, this is just lighting the firework stars on the ground. I've also made some 3mm firework stars with this composition. Some of them pop, break apart and each piece then pops, yielding a barrage of mini fireworks star bursts, but some go KABOOM in one fell swoop. I think all the firework stars probably all go KABOOM in a shell after priming where they get uniformly hot due to the speed of the inner prime. I believe the lighter I use doesn't evenly heat the firework star, so it sometimes breaks apart. A few of these firework stars that went KABOOM have left my ears ringing for the better part of 10 minutes - almost as loud as a regular firecracker! Can't wait to get some of these firework stars primed and into an artillery shell, a cake, or maybe even a small mine to see what they do in the air - definitely an effect you want to do at as low an altitude as you feel safe with (like maybe 50-60 feet).
I'm actually using Skylighter nitrocellulose lacquer thinned to about 8% (1 part 25%NC to 2 parts dried acetone).
The only thing I have a problem with in making the dragon eggs firwork stars right now is that you have to work really fast once you take a glob of the wetted firework star composition out of the closed Ziploc you've kneaded it in. The solvent evaporates so quickly that if you don't work damned fast, the surface gets crusty. Then, when you try and roll out the firework star patty for cutting or pressing through window screen, it cracks and crazes on the surface and firework stars composition flakes off. Sure, you can just accumulate the broken bits, dust and misshapen firework stars, rewet with straight acetone and do it all over again, but thatís tedious.
And just to give you a heads-up on the volume of 1.5-2mm firework stars you get from 20g of mixed composition, they'll fill a 35mm film can about 1/3 the way up - literally hundreds of tiny firework stars.
I'm also thinking that granulating the firework star composition through much thinner screen (20-30 mesh), where you wind up with firework stars closer to 1mm. This would allow them to be added directly to sky rocket compositions for what I bet would be a really "interesting" effect, especially if the prime you used on them was a color composition of sufficient thickness to allow them to exit the tail of the sky rocket before popping. Can't say I've ever seen a sky rocket that "back-fired" as it ascended.
The 75-15-10 firework star composition seems really good but as I said, thatís only on the ground. These firework stars need to be tested in the air. I also want to judge the difference in sound in the air between the 2mm firework stars and the larger ones to see if the difference is as noticeable in the air as it is on the ground. I kind-of think it will be, but you and I both know that firework stars sometimes surprise you once you get them into the air."
I asked if he had tried dextrin as a binder instead of the NC lacquer. Gene replied: "Haven't tried dextrin as a binder for these firework stars- not sure it would work but it would be cheaper and much less troublesome. It wouldn't surprise me one bit if the NC lacquer not only works as a binder but also as a fuel of sorts and that it needs to be there to make the reaction work properly. From my ground tests, it actually looks like the little firework stars heat up red-hot first and then blow. Maybe the NC is an intermediary fuel that sustains the precursor reaction. Itís such a good binder; maybe itís what provides the confinement prior to bursting that allows the firework stars to pop so loudly, it's just speculation on my part. I can't say I've ever seen a breakdown of the exact chemical reaction that causes the firework stars to pop so loudly so I don't know what the mechanism actually is. I have read that you never want nitrate to contact or leach into the firework stars as this will ruin the effect. Everything I've read suggests the use of a hot perchlorate inner prime with red gum, wetted with straight 70% isopropyl. At 70%, the red gum is going to probably nearly completely dissolve, providing a pretty nitrate-proof barrier. Also, something tells me that, if dextrin or some other water-soluble binder works, someone would have published some info on it already. Still, it wouldn't be a big deal to mix up 5-10g of composition and try it."
Keep in mind that this work Gene has been doing is very much a work in progress. But I think it does provide an interesting, less-expensive, and less toxic starting point for anyone who wants to make dragon eggs firework stars. If you try his pyrotechnic formulas you may want to experiment with dextrin or Starpol water-soluble binders in place of NC. Using NC and acetone is a lot more problematic, as Gene mentions.
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