Sometimes, learning how to make a colored smoke bomb can be tricky. Even if you think you already know how! You can still have problems getting your colored smoke to burn bright and without sputtering even if you’re an old pro at making smoke bombs.
Many people get their smoke supplies from suppliers that have been offering organic powdered dye pre-mixed with the other necessary colored smoke chemicals for years. These premixed colored smoke components make it a lot faster and easier to make smoke grenades and smoke bombs. Typically you can buy a pound of the colored smoke mix, combine it with a pre-measured amount of potassium chlorate (KClO3), load it into a capped tube, insert the Visco fuse and voila! You have a homemade smoke bomb, ready to light and enjoy. Usually smoke shops near me.
Occasionally I would have problems getting the colored smoke to light. When this problem became repetitious, I decided to roll up my sleeves and look into it. What I found was anything but earth shattering, but a good lesson in simple pyrotechnic detective work and it is exactly the same kind of problem diagnosis and solution process which anyone who makes fireworks will eventually run into.
The purpose of purchasing a colored smoke bomb kits is to make it simple and fast to make a smoke bomb. But suppliers perhaps have made it too simple, they may overlook the obvious. I was mixing the two-part colored smoke components (smoke mix and KClO3) correctly, according to the instructions my supplier provided but when I tried to light the newly assembled smoke bomb it wouldn’t burn or it would light and then sputter and fizz out.
Ideally when you light the smoke grenade it is supposed to smolder, not catch on fire. The key is having exactly the right ratio of the potassium chlorate oxidizer to smoke mix fuel. Wrong measurements in one direction and your mix will burn too fast and you won’t get the colored smoke you want, instead black, brown, or some other unimpressive colored smoke. Err in the opposite direction and your smoke mix will not ignite at all. Accurate measurements are critical.
I took my problem to my supplier and they jumped right in. They took samples from the batch of smoke mix that my kit had come from, identified by lot number, mixed it properly with the KClO3, and touched it off outside the office. They too, had some kind of a problem. Initial thought was that perhaps the lab which formulates their colored smoke mixes in large quantities, had changed the composition in some way. We called them up and they said nothing was different, but chemicals can vary from batch to batch and unless you do time consuming and expensive testing of each new batch you may never know.
We found that if we increased the amount of KClO3 added to the smoke mix, that we could get it to burn sometimes, the problem persisted. Then an idea pulled from the sky; one or both of the two-part smoke mixture must have gotten clumpy which happens when a powdered chemical gets a little bit of moisture in it thereby increasing the particle size. Upon close observation you could see that the KClO3 had indeed developed clumps. We sifted some of the blue smoke mix through a 30-mesh kitchen strainer and found the same thing. Theory confirmed! The thought that the powdered chemical composition in the kits was indeed subject to humidity and that this was affecting the burn was accurate.
When particle sizes are larger surface area is decreased. The pyrotechnic burn you need depends on many little particles of fuel and oxidizer being in close contact with each other. We were confident we had the mix proportions exactly right as long as the particle size was fine and free flowing. But with the humidity induced clumps the two powders now had decreased the interactive surface area which was no longer adequate for the recipe we were using. That’s why adding a little more potassium chlorate had solved the problem for some of the tests, the decreased surface area meant that if we changed the ratio of oxidizer to smoke fuel we could indeed get the smoke mix to light. There had to be a revision in the method of mixing and milling the chemicals and confirm the smoke fuel to KClO3 ratio.
Armed with the knowledge that it was indeed and merely a particle size issue, we set out to resolve the problem in a way that would involve the least hassle and expense, good ole trial and error. We worked with very small batches as to speed up the process by reducing weighing, milling, and mixing. It also reduces the cost of materials which may be wasted during the testing.
I don’t do this indoors any more as smoke dyes are easily blown around by even stray puffs of wind so my first problem was finding someplace that wasn’t windy. I found a protected corner against a shed, out of the wind, and set up my scale, two coffee grinders, some mixing cups, a small kitchen strainer screen, and my trusty pyro notebook. I aimed for a ratio of 14.2 grams of smoke mix to 5.2 grams of potassium chlorate. That’s the ratio we devised early on that would work with all of our smoke mixes, regardless of color. And we knew from history it would work. My test burn container for the following experiments was a 9/16″ ID x 1-1/2″ long tube (called an M80 tube in some circles) with a cardboard plug in one end, the other end open. (side note; colored smokes do not have to be confined to burn).
Experiment 1: I added the two chemicals together in a plastic zipper bag and kneaded them together for ten minutes. Filled a test tube, inserted a piece of Visco fuse and lit it. Failure to light. This mix would not even light when exposed to an open flame of a blowtorch.
Experiment 2: I repeated the process in Experiment 1, but with an additional 10% potassium chlorate. Lit the fuse, and it too failed to ignite. Blowtorching the loose mix caused it to light, but it could not sustain the burn, and went out.
Experiment 3: Repeated #2, again added 10% chlorate, instead of bag mixing, screened the mix 3 times. Lit the fuse, and the smoke mix ignited, the burn was sustained, but with a “sputtering” burn, and an okay, but not rich blue smoke.
Experiment 4: Since the potassium chlorate was the lumpier of the two components, I used a coffee and spice grinder to grind the chlorate to a fine, fluffy powder, with about 20 seconds of pulse milling. Weighed the two components in the original 14.2/5.2 grams ratio. Screened the two components together 3 times. The mix burned correctly.
Experiment 5: Repeated #4, but I also blade milled the smoke mix for 20-30 seconds as well, before screen mixing together 3 times. The mix burned even better. Full rich blue smoke. The volume of smoke was the greatest of all the test burns.
The particle sizes of both components need to be as small as possible. If there is a problem getting the smoke mix to burn, then milling both components separately to a finer particle size, as well as using a better mixing method will likely solve the problem.
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