Film Canister Firework Shells
This is a great project if you are new to homemade fireworks shells or are cursed with a small space in which to shoot your experiments. Thanks to John Shupe for providing this well written and clear article. This is a reprint of an article that originally appeared in the "The Fire Flies," the quarterly newsletter of the Michigan Pyrotechnics Arts Guild.
I was given a guest pass to the Pyrotechnics Guild International convention in Muskegon, Michigan in August of 1996. I hadn’t realized that such a thing even existed. I joined the PGI the following week. I started surfing the Internet and gathering information on pyro subjects. I soon learned to winnow the pyrotechnic wheat from the "kewl bomz" and "Jolly Roger’s" chaff. One article that caught my attention early on described making aerial firework shells using plastic film canisters. I tried it and liked the result. The following article details the methods I have used to construct film canister mortar firework shells.
First, Here are a couple of notes first. This article chronicles my experience building film canister mortar firework shells. It will quickly become evident to even the most casual reader that this article is not the final word on building these elegant little devices. These are the techniques and materials that have worked for me. I make no claim that the reader will get safe or satisfactory results based on the information in this piece. I will leave that determination up to the reader.
I would also like to acknowledge Dr. Stephen Haussmann of Athens, Georgia. Stephen has presented seminars on the construction and firing of film canister mortar firework shells at each of the last three PGI conventions, written articles on the subject for the PGI Bulletin, pushed the envelope of film canister mortar firework shell effects (including "stealth" lampares and mini crossettes), and has been an invaluable resource for me as I learn this craft.
Why build film canister mortar firework shells?
Film canister mortar firework shells are appealing on many levels. For the beginning firework shell builder, film canister mortar firework shells offer an excellent entrée into the world of firework shell construction. A careful builder can learn the basic concepts of simple firework shell construction and obtain satisfactory results fairly quickly.
Film canister mortar firework shells require minimal investment in construction materials, tools, live compounds, and equipment. Chances are, most budding pyros already own the simple equipment needed to build a film canister mortar firework shell. My basic toolkit consists of a hot-melt glue gun, a fine-tipped soldering iron, utility knife, and various homemade scoops. Mortars are built from commonly available materials.
Experienced pyros have found film canister mortar firework shells to be a convenient and practical way to test new firework star compositions, since film canister mortar firework shells can be fired immediately after construction. Often it is easier to judge the quality of a firework star composition when it is viewed as part of a group at 100 feet in the air, rather than a single firework star shot 30 feet in the air by a firework star gun. Film canister mortar firework shells have also been employed as sky rocket headings and inserts for larger firework shells.
Because of the smaller scale of the devices and the relative simplicity of the manufacturing process, building film canister mortar firework shells presents a somewhat lower risk factor as far as accidents are concerned. This is not meant to imply that the probability of accident is any lower. Indeed, proper pyro safety protocol must be followed at all times. But should an accident occur, you are typically dealing with quantities of live materials measured in tens of grams, rather than hundreds or thousands. This can be the difference between a severe burn and a traumatic amputation.
The intention of this article is to explain the basic techniques used in the construction of film canister mortar firework shells. The article assumes that the reader has access to basic pyrotechnic materials such as black powder, visco fuse, and nitrocellulose lacquer (NC).
Unless you are a very ardent photographer, you will need to locate a source for a supply of empty 35mm film canisters. Try to find a camera shop that caters to professional and advanced amateur photographers. These camera shops usually do film developing on site and typically amass large numbers of film canisters that they are more than willing to part with for free. The first time I went into my local shop I walked away with two grocery bags full and could have had twice that many had I wanted.
Film canisters come in two basic styles. The canisters used to package Kodak film typify one style. This type of canister is usually made of HDPE and has a lid that is larger than the OD of the canister itself. This style of canister seems to be the canister of choice among most film canister mortar firework shell builders, especially those working to perfect the symmetrical break.
The second type of canister is typified by the style of canister used to package Fuji film. This canister is usually made of a translucent plastic that is somewhat brittle. The lids on these canisters are effectively smaller in diameter than the body of the canister and snap into the canister lip rather than over it. Canisters of this type have been used in the construction of multi-break salami shells and are preferred by the author for building solid-state "stealth" lampares.
You may run across a third type of container in your bag of goodies from the photo processor. The new Advanced Photo System (APS) film comes in an asymmetrical canister that is unsuitable for mortar-fired firework shells, though they do show some promise as inserts for larger, conventionally built firework shells.
One of the most basic challenges facing any shell builder is devising a way to delay the ignition of a firework shells contents until it has reached a sufficient height above the ground to be both aesthetically pleasing and safe. Time fuse and rammed spolettes are the two most common devices used to accomplish this task in standard firework shell construction. Neither device, however, is optimal for film canister mortar firework shells. Because of the small scale of the film canister mortar firework shell, space is at a premium and the relatively large diameter of standard time fuse or spolettes leaves too little room for "payload". Instead, common green 3/32-inch visco fuse is modified to serve as a narrow diameter time fuse.
Because of the "side spit" inherent to visco fuse, some means must be employed to insulate the firework shell contents from the visco fuse’s fire until the appropriate moment. Several schemes have been devised to accomplish this and each has its proponents. Each general method is described below.
One method to create time fuse from visco fuse involves taking a short length of visco fuse and wrapping it tightly with two or three layers of aluminum foil. Care should be taken to make sure that the foil conforms closely to the surface of the visco fuse. The foil-wrapped visco fuse is then wrapped with an additional two layers of masking tape. This method creates a reliable time fuse.
A variation on this method involves using electrical shrink tubing in place of the masking tape. The tubing is slipped over the foil-wrapped visco fuse and then shrunk using a heat gun set on low heat. This method creates a reliable, and slick looking, time fuse. I am not convinced, however, that this method offers a big enough performance advantage to offset the higher cost of materials and the additional risk of using a heat gun around energetic compounds.
Yet another method uses a thick layer of hot melt glue, applied to the visco fuse during the installation of the visco fuse into the canister lid or body, as a barrier. This is the method that I used when I first started building film canister mortar firework shells and it works well. But it has several drawbacks. The method can be inconsistent and great care must be taken to apply a uniform and adequate coating of hot melt to the visco fuse, with particular caution paid to eliminating air bubbles from the coating. This method is really only suitable for fusing film canister mortar firework shells through the lid, since free access to the visco fuse on both sides of the firework shell wall is required. This method can be both messy and irritating since it requires fairly large gobs of molten glue and all the attendant mess and risk of burns until the glue cools. And of course there is the added risk of using a hot glue gun around bare visco fuse.
My preferred method involves simply wrapping a short length of visco fuse with four or five layers of 1" masking tape, eliminating the foil used in the first method described above. I have found that 1" tape affords a nearly ideal delay for the typical film canister mortar firework shells. Some film canister mortar firework shell builders have expressed concern that a simple tape wrap around the visco fuse, leaving out the foil layer, can lead to a "quickmatch" effect. I have not experienced this particular failure in several hundred film canister mortar firework shells and consider it unlikely to happen if sufficient care is taken to wrap the tape tightly around the visco fuse. I usually make the time fuse as a separate operation from firework shell construction and will usually make enough time fuse during each session to meet my anticipated near term needs.
Using a utility knife with a sharp blade, cut enough green 3/32-inch diameter visco fuse into shorter 1-1/2-inch pieces to meet your needs. For each visco fuse piece, use a 2-inch length of 1-inch wide masking tape. Position the masking tape so about the same amount of bare visco fuse is exposed on either side of the tape. Tightly roll the masking tape onto the visco fuse. A 2-inch piece of tape will wrap around the visco fuse about four times. The end result will look like a hot dog, with the green visco fuse "sausage" protruding past either end of the masking tape "bun". The protruding ends will be split and primed later in the building process.
How to Make a Stealth Fireball Shell - "Lampare"
One dilemma universal to all beginning firework shell builders is question of what to put inside the firework shell. For most beginners, access to bulk firework stars or other professional inserts is limited. Traditionally, Class C (1.4G) fireworks have provided a ready source of insert material, either through "repurposing" firework stars scavenged from marginal cakes or candles or by using Class C devices themselves as inserts (bees, jumping jacks, and firecrackers come immediately to mind). I have had good luck with Class C inserts, using a gram or so of 3FG black powder as burst, though I would recommend priming each device with nitrocellulose lacquer and meal powder.
Most builders will eventually want to move on to other effects. One of the great pleasures of building your own firework shells is the opportunity to create effects not usually seen in commercial product. One of my favorite effects is the aerial fireball, or lampare, effect. In large-scale fireworks, creating a lampare involves lifting a firework shell consisting of a gallon or so of volatile liquid in a plastic bottle and a charge of several ounces of flash powder. The firework shell is timed so that the flash powder charge ignites at the apogee of the firework shell’s flight, simultaneously dispersing and igniting the liquid. The result is an angry red fireball shot through with tendrils of malevolent black smoke, inevitably eliciting atavistic grunts of admiration from the pyros in the crowd. A similar effect can be easily and relatively safely recreated, on a smaller scale, using film canister mortar firework shells.
The "Stealth Lampare" (so-called because it produces the fireball without the loud report of a traditional lampare) uses a solid-state mixture of powdered naphthalene and black powder. The naphthalene is obtained from common mothballs. The mothballs are "baggie-milled" by being placed in several layers of plastic bags and then crushed using a mallet. The crushed naphthalene is then sifted through a window screen, with the finings that pass through the screen used in the mixture and the chunks that stay returned to the baggie for additional "milling." The naphthalene powder is combined with meal powder in a weight ratio of 2:1. The resulting "salt and pepper" mix is then used as filler in the film canister mortar firework shells.
I use the following process to build a film canister mortar firework shell lampare:
Remove the cap from a Fuji-style film canister. Create a 1/8-inch hole in the bottom of the film canister body. Any of several methods can be used to create the hole. I use a pencil type soldering iron with a narrow tip to melt a hole. I have also used a 1/8-inch drill bit chucked in an electric screwdriver or a scratch awl to make the visco fuse hole. The most important thing is that the hole be just big enough to let the prepared time fuse fit snugly.
Take a tape-wrapped visco fuse and, using a sharp utility knife, cut the exposed visco fuse on either side of the tape on an angle. The idea here is to expose as much of the powder core of the visco fuse as possible. Dip one end of the visco fuse into NC lacquer and immediately dust with meal powder. This primes the visco fuse, ensuring the transfer of fire from the visco fuse to the firework shell contents (figure 2).
Using needle nose pliers or a hemostat, grasp the unprimed end of the time fuse. Thread the visco fuse through the hole in the bottom of the film canister from the inside of the canister, taking care not to damage the exposed visco fuse. The visco fuse should end up wedged snugly through the hole in the bottom of the canister, with the primed end of the visco fuse situated inside the canister body. Carefully position the visco fuse so it is approximately centered in the hole.
Apply a generous gob of hot melt glue to the junction where the masking tape-wrapped visco fuse meets the outside bottom of the film canister mortar firework shell. Avoid touching the tip of the gun to the exposed visco fuse. I have never had the visco fuse ignite from the heat of the glue gun, even when deliberately touching the gun directly to the powder core, but prudence is always the wisest course when dealing with fireworks. Once the glue is applied, I like to give the visco fuse a quick twist in the hole to make sure that there is a good seal between the visco fuse and the firework shell wall. A good seal is essential to ensure that the fire from the lift charge cannot pass prematurely to the contents of the firework shell. Set the fused film canister mortar firework shell aside to cool.
After the glue is cool, fill the firework shell with the "salt and pepper" mix. Fill the canister about 3/4 full, clean the lip of the canister, and snap the plastic lid in place. Make a single wrap of masking tape around the top of the shell, overhanging the edge by about half the width of the tape. Pleat the overhanging tape down onto the lid. Other than this, done more for a fire seal than anything else, no spiking is required for film canister mortar firework shell lampares. Indeed, over-spiking the firework shell will cause it to function as a weak salute, rather than create a fireball. Dip the exposed visco fuse into NC lacquer and dust with meal powder.
At this point you can add a lift cup and leader or use the firing scheme described below. To add a lift cup, I have found that the pleated, white paper catsup cups from fast food restaurants work quite nicely. Attach a quickmatch leader, long enough to reach up and out of the mortar being used, to the cup with a dab of hot melt glue, making sure that a sufficient length of black match is exposed in the bottom of the cup. Place about 9 grams of 3FG black powder in the cup. Apply a generous bead of hot melt glue around the perimeter of the bottom (the end where the time fuse is protruding) of the film canister mortar firework shell (again, taking great care to avoid touching the primed visco fuse) and immediately apply the loaded lift cup to the firework shell. In most cases, the primed visco fuse is in direct contact with the lift charge. I have yet to have an ignition failure with a primed visco fuse/lift cup combination. Finish the firework shell with a piece of visco fuse attached to the end of the leader. Film canister mortar firework shells prepared in this manner can be fired from any sufficiently stout 1-1/2 inch ID plugged tube. I use tubes constructed from Schedule 40 PVC pipe. Each tube is approximately 12 inch long, and each is plugged with a standard PVC cleanout fitting.
I would like to make a note here on the use of PVC pipe as a mortar material. Because of its tendency to create sharp, jagged shards when shattered, PVC has been frowned upon as a mortar material for commercial displays. However, when used to shoot film canister mortar firework shells, Schedule 40 PVC has proven to be a safe, durable and reliable mortar material. As always, the PGI table of distances should be consulted and adhered to.
A second type of firing system does away with the need for a lift cup and consists of a mortar built from Schedule 40 PVC pipe plugged with a cleanout fitting as described above. The cleanout fitting consists of a threaded female part, which is attached to the tube with PVC cement, and a threaded male plug that screws into the female section. The interior of the male part has a cubic recess that is expressed as a protrusion on the outside of the plug. This recess holds just about 9 grams of 3FG, which also happens to be the ideal lift charge for a film canister mortar firework shell. To take advantage of this happy coincidence, one only has to drill a 1/8-inch hole through the wall of this recess. This allows a length of visco fuse to be threaded through the hole and into the recess. The recess is then filled with 3FG and the plug is threaded into the tube. The film canister mortar firework shell (without lift cup) is then loaded into the tube. The primed time fuse is automatically centered in the lift charge. The visco fuse leading from the plug is lit and the gun functions just like a conventional system.
On June 30, 2000, the film canister mortar firework shell Stealth Lampare made its first recorded appearance in a commercially shot public display. Summit Pyrotechnics featured a 12/20/40-shot barrage, built by the author, in a small-scale show shot in Muskegon, Michigan. The effect was well received, and integrated nicely into the rest of the show.
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