The Rising Comet Effect

by Victor Chaney

When shooting my handmade firework shells, I just love putting a comet onto my shell. It adds a beautiful trail to the shell, helps me spot it and know where it is going to explode, and "more is better", right?

I find that there are two problems with this. First, is getting the thing to stay on the shell. Second, is getting a good formula to have a nice trail of sparkles and glitter.

Now, making the comet stay on the shell and survive the blast of the lift charge is a problem.

If you ask 10 different pyros how to solve this problem, you will get 12 different answers.

I asked a very knowledgeable fireworker what to do, he told me his solution, and then I watched his shell go up while losing the comet halfway up.

The comet needs to survive the blast of the lift, and then it needs to stay with the shell all the way up.

I think I have found a good, workable solution.

I have made a paper mâché comet holder that is strong and glues easily to the top of a shell with hot glue.

This helps it survive the lift blast. But then the comet can still fall out of its holder on the way up.

This comes from two reasons: first, the comet can burn away part of its holder, and second, some of the comet can burn away, become smaller, and just fall out of the holder.

My paper mâché mix has sodium silicate solution in its ingredients, which adds a fireproofing component to the holder. Also, the holder is narrower at the top, and wider at the base, so that if some of the comet burns away, most of it is still too big to fall out of the holder. 

Watch the video to see how it is all done:

Supplies

1. Mod Podge Matte for the paper mâché (Amazon.com or your local crafts store). This is a thick version of white glue. Mix the water and the Mod Podge first, then add the sodium silicate solution so you won’t get lumps. The 8 oz. size will make about 60 comets.
   
   
2. Sodium Silicate solution (Skylighter CH8287) to fireproof the paper mâché mix.
   
   
3. Brown craft paper (Amazon Boardwalk K2440900 Kraft Paper, 24" wide) cut into circles: I use two strips of paper 2 3/4 inches wide, fold them over several times into a square, and then cut a bunch of 2 ½” circles at the same time. Five circles per comet holder.
   
   
4. Strips of brown paper 2 5/8" wide * 24" long. One strip per comet forms the tube.
   
   
5. Strips of brown paper 5/8" wide * 12” long, one strip per comet to reinforce the union of tube to circles. Another strip 2” long to hold the narrowing crimp in place.
   
   
6. Plastic wrap to cover a hemi to build your comet holder on.
   
   
7. Hemis to build your comet on, and clothespins to hold the plastic wrap on. The clothespins can come off while the comet holder dries on the plastic wrap and hemi. A 1-quart paint can makes a nice stand for a 6" hemi.
   
   
8. Piece of PVC pipe 1-1/8” diameter and 1-1/2” long to form the tube. I made a line at 1".
   
   
9.  Dowel 3/4" diameter to pack the comp into the tube. 
   
10. Chemicals to make the comet composition (see recipe below).
    
    
11. Duco cement (Amazon) for priming.

The Comet Holder

This involves making a paper mâché holder that can be hot-glued to the top of the shell.

 These can be made in advance of making the shell and then glued on at the time of adding the lift and fusing to the shell.

I am using 6" shells, and for different sizes you would need to adjust the proportions of it all.

Paper mâché recipe: Mix the Mod Podge and the water first, then add the sodium silicate solution.

The video of the comet holder construction shows how this is done:

I highly recommend using disposable materials for using the paper mâché mixture, like plastic cups for mixing, and an aluminum pie pan for holding it. It is hard to clean up.

You start with brown Kraft paper.

A hemi is covered with plastic wrap, held in place with clothespins.

A base is added with 5 circles of paper, and then a cup is formed with a strip of paper, stuck onto the base, and then a thin band of paper is formed around the junction to hold it all in place.

The top of the tube is twisted/folded to make the tube narrower at the top than at the bottom.

See the drawing above of folding the top of the tube.

I used tin snips for cutting, because of their better leverage when cutting thick stacks of paper, but scissors are fine, too. Put some WD-40 on the hinges of your tools (“WD” stand for Water Displacement) before and after to keep away rust.

After it all dries, the cup that is to hold the comet is trimmed to the correct height (it trims more easily when the whole thing is dry).

It is best if the comet keeps burning until the moment the shell blows, but not earlier or later than that moment. For my 6” shells, one inch in height is perfect.

Different formulas may burn at different rates, so if you use different formulas from mine, you may want to adjust the height of the comet.

My comet-forming piece of PVC pipe is 1-1/8 inch in diameter. A taller comet will burn longer, and a larger diameter will give a bushier tail.

Bigger is better, but you must consider how much room there is for the comet, and bigger is more expensive with the ingredients. My example shell in the video seems about right to me.

Then the comet composition is packed into the holders.

I made a 3.5” circle of wood to support the comet holder. Then I rounded it to the shape of the hemi, and set that on top of a pounding post.

The composition is put in, using 3 to 4 layers, packing each layer with a 3/4" diameter wood dowel and a plastic mallet.

My formula (in theory) does not need priming, since it has a lot of black powder in it. But it is only going to get a brief exposure to flame when the lift charge goes off below.

So, I prime it by putting an “X” of Duco cement on the top, and then dipping that wet glue into black powder in granulated form.

Use smaller granules that you might use for lift powder.

One way to get this is to grind some lift powder into smaller granules with the back of a spoon on a pie pan, or a mortar and pestle, or just buy some finer granulated black powder.

The granules of black powder are rough, stick up a little on top of the comet, and grab the flame very well from the explosion of the lift charge.

Duco cement is essentially nitrocellulose cement. If you don't have Duco cement, you could also use some nitrocellulose dissolved in acetone to make a thick glue.

Maybe this priming step is not always needed, but it is a shame to go to all the work to make a nice comet, and then not have it light!

The assembly is glued onto the top of the shell with hot glue.

The hot glue should be applied in liberal stripes in parallel on the bottom of the comet holder, and then this is stuck onto the shell.

Parallel stripes give channels for air to escape and allow for better glue coverage.

The gluing area will distort slightly during drying of the paper mâché, so generous beads of glue are a good idea to make sure the glue is really holding the comet to the shell.

The Composition Formula

I tried a bunch of different formulas to make the comets.

I used some red rubber star comp, and it seemed to almost explode partway up and separate into different pieces. I think it may have burned too fast.

Different compositions burn at a different rate, and so a different height of comet may be needed for a different formula or for a different sized shell.

I have tried using pre-made, store-bought comets. They are primed all over, and when the comet lights the burning goes right down the outside of the comet and releases it from the paper tube holding onto it, and off goes the comet on its own separate journey from your shell. Also, they came in a tube all set to launch it, and getting the comet out of the tube took a little too much work.

A lot of the glitter formulas use water (often 2/3 water and 1/3 alcohol) and dextrin as a binder. I really like using acetone and red gum, as it dries fast, and there is less danger of the comet not being dry enough.

I asked a fireworking PhD about whether it would matter to use the same formula but substitute red gum for dextrin as a binder, and acetone for water as a solvent. He did not seem to know and suggested that I try them both. So that is what I did.

I made four formulas for comets, our group put them on 53 shells, filmed them, and then I could see which performed better.

All of my comets were dried for 5 days outside, and then 2 days in a heated forced-air drying box.

First, I made a Silver Streamer mix.

Then I made two gold glitter formulas (the precursor to D1 glitter but supposed to be a little better). One of those had dextrin/water, and the other was identical except for using red gum/acetone. The red gum/acetone was better than the dextrin/water! It seems to me they should have been about the same.

The fourth was my own concoction with a lot more metal in it and some larger particle sizes of metal. I thought it was the best! This is the formula that I used:

There are about 23 grams of dry powder of this mixture per comet.

Screening metals is not a great thing to do, and the black powder is already mixed, so I put the dry chemicals into a big plastic container and rolled and shook it all for 5 minutes.

 The acetone amount is a good starting place, so put most of it in and save some to add until the right consistency is reached. It should be a somewhat dry mix, with just enough acetone to make it stay together.

If you do not have milled black powder, you can make “green” black powder with Potassium Nitrate, Charcoal, and Sulfur (75:15:10) by shaking it, screening through a 40 mesh screen, do this 3 times. It is not as “hot” as black powder but will probably work just fine.

Conclusion

Is this a lot of trouble? Not much more than other methods, and it works. 
Have fun with beautiful tails on your shells!