Close your eyes and listen to this music. What do you see when you do so?
If you don’t see a large fireworks mine-shot, followed by a line of 30-second strobe pots, ending with another large mine-shot, then you really need to be subscribed to the Quilting-101 newsletter instead of this one on making homemade fireworks.
Man, that music gets me in the mood for strobes. The first mine-shot would grab the attention of any fireworks-display audience. Then the soft and subtle section of strobes would calm them down and get them ready for their emotions to build during the show.
Strobe pots are among the simplest of fireworks devices and are easy to make. They can really add some of that low-level variety to a pyro-display that so helps to keep an audience’s attention.
“Hey, here’s something different,” they’ll say to themselves as they stop, settle in, and start to pay attention.
How do these pyrotechnic “twinklers” work?
It is not necessary, of course, to have a scientific understanding of strobes in order to make them. Like baking a loaf of bread, chemistry is not necessary. All you need is a recipe, the right ingredients, and a feel for the proper ways to manipulate those ingredients.
But, for the scientifically minded, there are a few informative resources, which explore the strobe phenomenon in depth. In the 1979 edition of Pyrotechnica, Number 5, Robert Cardwell, the editor and publisher of the Pyrotechnica series, wrote an article, Strobe Light Pyrotechnic Compositions: A Review of Their Development and Use.
In this essay, Cardwell explores the historical development of strobing compositions and presents quite a few different formulas.
Dr. Takeo Shimizu, in Fireworks, the Art, Science and Technique (FAST), originally published in 1981, writes about “Twinklers,” which is how he refers to strobing stars. He presents an outline of the development of these strobing compositions, progressing during the second half of the 1900′s.
Specifically Shimizu writes, “In Germany, U. Krone and F. W. Wasmann suggested that a twinkle composition consists of two kinds of compositions mixed with each other, i.e. a smolder composition and a flash composition-Ammonium perchlorate smolders when it is mixed with a small quantity of magnesium. This can be used for the smolder composition. A mixture of magnesium and sulfate flashes when it is heated to a high temperature. This can be used as the flash composition.”
So, interestingly, a strobe composition is actually a mixture of these two types of comps, a smoldering one and a flashing one. When the mixture is lit, the first one begins to smolder. When the heat rises high enough, the flash comp ignites and emits a flash of light and heat. Then the mass returns to the smoldering state until the heat rises high enough to repeat the flash.
In some compositions, magnesium-aluminum (magnalium) is used instead of the magnesium. Magnesium requires a coating to prevent it from prematurely reacting with the oxidizer in the comp.
Additionally, sometimes barium nitrate or other oxidizers are used instead of ammonium perchlorate.
In 1987, John “Skip” Meinhart offered some details about his noteworthy strobing star formulas in Pyrotechnica XI. Except for Shimizu’s White formula, and Skip’s Pink formula, all the rest of the formulas use magnesium as the metallic fuel ingredient.
In the 1992 Pyrotechnica XIV edition Jennings-White explores Blue Strobe Light Pyrotechnic Compositions. Up until that point in time, blue strobes had not been explored in depth because of some unique problems associated with the chemical mixtures required to produce that color in a strobe.
All of this information ought to be able to keep you reading until late into the night if you are so inclined.
Making strobe pots
I won’t be focusing on making strobing stars in this project, but only simple, ground-effect strobe pots.
I’m also not going to be making any of the formulations, which contain magnesium. As I said, using that metal requires a special coating process because it does not form an oxidized protective layer on its own, as do aluminum or magnalium.
There seems to be some debate as to whether or not magnalium needs to be treated and coated when it is used in compositions containing ammonium perchlorate. Meinhart states, “I have had success using magnalium powders that have not been treated with potassium dichromate. In practice I have often used treated metal powders, but this does not always seem to be necessary.”
Whereas in Hardt’s Pyrotechnics, Barry Bush notes that the formulas he cites which contain magnalium or magnesium in combination with ammonium perchlorate do “require the metal powders used to be treated with potassium dichromate.” Shimizu also specifies treated magnalium, and details the methods of treatment in FAST.
Shimizu does state that if there is any reaction between magnalium and ammonium perchlorate, which would be encouraged by the presence of water, it would only be a slow reaction in which the metal is affected gradually.
I have used untreated magnalium in these formulas, with no problems. One sign of an unwanted reaction would be the heating-up of the composition as I’m working with it, so I always pay attention to see if that is occurring. I avoid adding any water to such a composition. I also don’t store these devices for long periods of time, which could produce a slow reaction of the ingredients, especially in the presence of moisture.
So, I think I’ll make simple white and pink strobe pots. The white formula is the most commonly cited one.