Double Petal Shell (6")

From PyroGuide

A Double Petal Shell is an aerial shell that produces not one but two spherical groups of stars, called petals. Each petal of the aerial shell requires its own individual group of stars, as well as a break charge to break the stars into their correct peony shape. This is typically done by placing an already made shell hemisphere inside of another. In essence, there will be two simultaneous shell breaks, one inside another. (See image)
Most commonly, these shells are made with colored stars so it is a peony effect, but this is not mandatory. In this tutorial, I'll be showing you how to make a 6" double petal using red, white, and blue stars. (It's a 4th of July finale) Note that it is recommended that a double petal shell be at least 6" diameter for a proper effect. It is possible to create the effect with slightly smaller shells, but never use smaller than a 3" outside shell. In general, a smaller shell will not leave enough room for the necessary components.

Contents 1 Materials 2 Formulas 3 Procedure 4 Video

Materials

• Stars - for this shell, I'll be using 3/4" red and blue stars, pumped from a standard Wolter pump. I'll also be using some 1/2" pumped white stars for the center section of the shell.
• Shell hemispheres - a 6" round shell. Also you'll need either a paper 3" hemisphere or a 3" sphere to make your own 3" hemisphere out of. The small hemisphere needs to be very thin, just enough to hold the material you put in it, and separate it from the surrounding material.
• Break Charge - I'll be using meal-coated corn cob to break this shell.
• Lift charge - Pulverone Black Powder will work well for lifting this shell.
• Time fuse or Spolette - 1/4" chinese time fuse is great for timing purposes.
• Quick match or an Electrical Ignitor as a main fuse for your shell.
• Hot glue gun - for gluing your timefuse into your shell and attatching the lift charge
• Plastic straw - for your powder core to help fuse the shell.
• Tissue paper - I chose some festive stuff.
• Note the Mountain Dew, which helps dramatically re-energze during this long process.

Formulas

Veline's Blue

Veline's Red

Grant's "Garage White"

Potassium perchlorate	54
Barium carbonate	26
Red gum	6
Antimony trisulfide, Chinese Needle	5
Magnalium, -200 Mesh	5
Dextrin	4

Procedure

PART 1 - CONSTRUCTION

Begin by setting up your 6" shell hemispheres on hollow cylinders of some sort. For smaller shells, paper towel tubes cut short work well. But for a 6" shell, something a little more stable is required. I use short sections of 4" PVC pipe that are excess after cutting my mortars.

Plug in your hot glue gun and let it get to temperature. You can use alternative methods to set your time fuse, but I prefer hot glue because of the seal it gives your shell during lift. Without that hard seal, fire could manage to slip past your time fuse and cause your shell to Flower pot. Cut a piece of time fuse 1-3/4" long with a razor blade. Do not attempt to use scissors or other pinching devices, as these will not cut the fuse cleanly and will break up the powder core, causing the fuse to burn faster or unreliably.

Take the hemisphere with the fuse hole (or for paper, the one in which you wish to put the fuse in) and insert the fuse about halfway into the shell. Put down hot glue all around the fuse on both the outside and the inside. This insures a tight fit and sealed shell. Place the plastic straw you have over the time fuse and also hot glue it to the fuse. Next, you must cut the straw the appropriate length. It must be no taller than the lip of the 6" shell you're working on. The best advice is to use a ruler across the shell to find where to cut the straw. You'll now need to cut a small hole in the side of the straw about 1" up from the bottom from where the fuse is. (See image above) This cut should be put where the outside break charge is located. Don't worry about cross matching your shell's fuse until later.

Next, you'll need to figure out how you'll load the shell with stars. For example, my shell will contain blue stars on the top, and red stars on the bottom. You could also take the time to make a left to right color assembly, but this would take a considerable amount of time and patience as you could not mix up the two colors. So I'm going to load the blue stars in the bottom hemisphere first (the half with the straw). Make sure the stars do not extend above the lip of the shell. Next, you'll need to cut a piece of tissue paper large enough to line the stars and contain your break charge. Cut a small hole in the middle of the paper to slide the straw/fuse into. The tricky part is dumping yor break charge into the paper. All at once dump a large cup of break charge into the tissue paper, letting it fall to the bottom of your shell and push against the sides. This will keep your stars from falling into the bottom of your shell.

The next part is what sets a double petal shell apart from typical aerial shells. You now need your smaller paper shell hemisphere. (Preferrably 3") Drill a hole in the hemisphere that is slightly larger than the outside diameter of the straw you used in the 6" hemisphere. Slide this hemisphere into the 6" hemisphere putting the straw through the hole you just made. You'll need to make sure that the top lip of the 3" hemisphere is even with the lip of the 6" hemisphere. If not, you will have to move some of the break charge from underneath to make it right. Once you have positioned your inner shell, you can fill the outermost portion the rest of the way with break charge. Or, if you had too much, take some out to even it out.

Line the inside of the smaller shell with stars. Here I'm using white 1/2" stars. Cut another piece of tissue paper to go inside this shell, also with a small hole for the straw. Fill this shell the same way with break charge. A little extra break in the shell will not hurt, so long as it is not way too much. The extra will make for a very tightly packed shell, and will be much less chance of the shell experiencing set back at lift.

Using the remaining 6" and 3" shell hemispheres, pack the red 3/4" stars, break charge, the remaining white stars and break the same as the already prepared hemisphere. The only difference in this half is there is no annoying fuse in your way. Once you have both halves completed, put a small scoop of whistle mix into the center of the inside shell. This will help the shell break harder and more evenly. Some professionals like to use flash powder, but stick with whistle. Flash frequently breaks the shell to hard and fast, shattering your stars or blowing them blind.

PART 2 - CLOSING
Once you've completed assembling the insides of your shell, only one task remains to close it. In closing your shell, you must be precise and quick. The easiest way to do it is simply to snap it shut from the bottom up. Some people use the cardboard or table edge approach for their shells, but I've found that doing it that slowly can cause your shell's components to loosen and/or move around. Plus, for this particular type of shell, there is a higher risk of movement causing a problem. Stick with the snapping method.

First, make sure that any and all traces of break charge or any powders are removed from the inner and outer lips of your shell hemispheres. This will make snapping them together much easier and foolproof. Not to mention if a bit of powder prevents you from closing the shell what kind of mess you'd have if you had to open it back up. Once clean, hold the hemispheres side by side. Slightly tilt them towards each other, and begin to line the lips up. In one quick motion, push both hemispheres towards one another and snap them shut. Experience helps in doing this. If you want some experience in closing shells, I recommend making smaller ones first, or simply filling your shell of choice with dry, non-powdered rice hulls or corn cob. Use this shell as a learning tool, as it will make much less mess than one ready with pyrotechnic material.

Using Methylene chloride (or another suitable PVC solvent), proceed to glue the shell together. I simply use testors model glue, as it melts polyethylene and polyvinyl plastics, and it comes in an easier-to-use gel or liquid on a brush. Wipe any excess solvents off the outside of your shell with a paper towel, and push it together tightly for a few minutes. Once dry, I like to wrap some paper tape or masking tape around the shell and across it to keep it closed until its time to wrap it.

PART 3 - WRAPPING AND FUSING

The 3 strip pasting method is used for wrapping the shell until it reaches the desired diameter. It should take between 12 and 16 layers to be the right diameter, depending on the weight of the paper you used and the type of glue. If you use gummed paper, you will probably be closer to the 16 layers. But if you use pretty thick (40-50lb) paper and wheat paste, you might only wrap 10 or 12 layers.

Once finished wrapping your shell, it needs to dry overnight or for a few days. The next step will be the fusing and finishing of the shell. First thing is you need to weigh the finished weight of your shell. This will give you a figure on which to calculate your lift charge. I had to go out and buy a new scale for this 6" shell because it was way heavier than my 250g digital scale. A packing scale will work, but you should find a scale that's at least within a couple of grams accuracy. If you used a packing scale, make sure you always add a little extra weight in lift in order to not underlift your shell.

Find the weight of your shell, and divide by 10. This is the weight of lift powder you will need to send this shell in the air. Your 6" shell should weigh approximately 1100-1300g, depending on the type of stars and how you packed it. This shell ended up weighing roughly 1220g. That weight would give you ~122g of lift as the weight to lift this shell. I always like to lift extra for reasons of safety, so I'll use somewhere around 130g of lift. Not to mention the wrapping and rising tail that I'll be adding to this shell will undoubtedly be adding some weight. However, your shell may be different, so you must weigh it to make sure. You'll need a rather large lift cup to accomodate that amount of lift. I recommend making your own cup out of paper or finding a large paper drinking cup that will work.

I'll be measuring out 130g of pulverone lift powder for this shell, and setting it aside temporarily. Take your e-match (or quickmatch) and use a little hot glue to stick it down to the bottom of your lifting cup. I simply run the attatched lead along the inside of the cup and make a small slit in the top of the cup to bring it out and as to not hold the lift cup away from the shell for easier glueing. Once the hot glue is cooled, you can go ahead and dump the lift powder you measured out into the lifting cup. Make sure that the cup is big enough, but not too big by softly setting the shell down onto the lift cup. Watch as the shell comes to rest on the cup for where the timefuse touches the lift powder.You want the timefuse on your shell to sink a little bit into the powder, but you don't want to have to move any powder in order to completely set the shell down. If it's good, then remove the shell and grab a piece of black match or another type of cross matching material.

The easiest and most efficient way to cross match your shell is not by cutting into the time fuse, but to lap the blackmatch across the powder core of the time fuse. By doing this and holding it in place with some thread, you ensure that your shell will light upon effect time. Once you have your match on, you can place your shell on your lift cup and hot glue it down. Make sure you put hot glue all the way around to make sure you get a tight seal.

PART 4 - TAIL AND FINISHING If you would like to add a rising tail to your shell, you first need to press a rather large star or comet out of the composition of your choice. I'll be using a red, a glitter, and a whistle formula in separate comets for a greater effect, but you can use any type of effect you want. So wet some of the formula you want to use, and press it with about a 1" star or comet pump. Depending on the composition, you might be able to press it smaller or have to make it larger. Burn time testing is recommended, though not required. Do not prime the comet except for on one end only. Once dry, use some craft paper to wrap around the comet, leaving the prime up top uncovered, and extending the paper down past the bottom of the comet. This extra length will be cut into strips and pasted onto the shell much like the wrapping was.

Video

Sadly, 4th of July came much too quickly this year to gather all the pictures I needed for this tutorial. However, I did get a video of the shot, from quite a distance though. Fog and rain set the show back, and didn't allow the camera to see the white center petal in this shot from 1500 feet away. Spectators however swore it was there and I saw it myself from straight underneith. Maybe next year I'll be able to get a better video and clean up this tutorial. Until then, good luck.
6" Red, White, and Blue Double Petal - 550KB