Pyrotechnic Formulas and Techniques For Making Fireworks Comets
Comets are really nothing more than an oversize cylindrical firework star fired from a mortar to produce a single rising effect in the air. Like firework stars, comets can be made in numerous variations such as color, tailed, strobe and crackling, even sandwiched combinations thereof. While many firework star formulas will work as-is for comets, some formulas, particularly color ones, need to be modified to burn faster if used for comets, in order to prevent the comet from coming back down to ground while still burning. Comets are especially effective if fired in multiples, arranged in straight, fan shaped or angled setups and fired electrically. However, careful attention must be paid to the fabrication of the comet itself and to the loading of the mortar in order that all the comets burn out at the same time after rising to a consistent height.
Several methods can be used to shape the cylindrical comet pellet. While there is no standard dimension where a firework star becomes a comet, I like to think that anything 3/4" in diameter or larger is a comet, and anything under 3/4" is a firework star, although there is no clear distinction.
1. Comet Pumps. These are a great way for an individual to get started making comets. In their simplest form comet pumps consist of nothing more than a solid wood or metal rod, with a close, sliding fit in a short length of metal tubing. The rod is first slid part way into the tube so as to leave an empty cavity at the bottom of the metal tube. The rod should extend several inches above the top of the metal tube (or "sleeve", as it is sometimes called). Firmly gripping both the rod and the tube at the same time, the two pieces are plunged as a unit into a dampened comet composition, filling the empty cavity in the metal tube. Next, the unit is set upright on a solid surface and a number of firm blows with a non-sparking mallet are delivered to the top of the rod to consolidate the comet mix. Lifting the comet pump up, the rod is pushed further into the tube, thereby ejecting the comet out the bottom. Generally, the comet will stick to the end of the comet pump rod and will need a gentle twist to release it.
Advantages of comet pumps:
Inexpensive, low-tech way to make comets
Easy to vary the thickness of the comet
Possible to make very hard, strong comets
Great for making small, experimental batches of comets
Disadvantage of comet pumps:
Slow, not suitable for production runs
2. Comet Plates. Plates produce a number of comets simultaneously. They consist of a thick metal or plastic plate into which round holes have been bored the same size as the comet diameter. This is called the hole plate. The thickness of the plate is about 10% greater than the height of the finished comet it produces. Another comet plate, called the pin plate, is machined with a series of round pins protruding down from the bottom of the comet plate. These pins are roughly 0.030" smaller in diameter than the holes in the hole plate. The length of the pins is roughly .060" longer than the thickness of the hole plate. The pins are arranged so that they slide easily into the hole plate. A comet (or firework star) plate is nothing more than multiple comet pumps ganged together. Comet plates can be used in hydraulic or pneumatic presses to consolidate the comet composition or they can be operated entirely by hand and do not require machinery of any kind. The exact procedure for operating the comet plates by hand is somewhat difficult to describe and is best learned by watching a demonstration, as available in DVD Star Making Troubleshooting.
Advantages of the manual comet plate method:
Low-tech, fairly inexpensive method to quickly produce large quantities of comets. My favorite plate produces twenty-seven 1-1/2" diameter comets each time it is filled, and in one and a half hours can turn out 100 pounds of comets utilizing nothing more than muscle power.
The comet plates are portable, can be set up anywhere, and are easy to clean.
Disadvantages of the manual comet plate method:
Comets are not as hard as when using a single comet pump or a press
Height is limited to the thickness of the hole plate
Large diameter comets tend to be "hockey puck" shaped due to limitations of trying to consolidate a large thickness of composition
Comet compositions must be dampened very carefully; too dry, and the comets will not hold together when fired; too wet, and they will stick to the pins when they are ejected from the hole plate
Not suitable for shock sensitive comet formulations
Limited to 3" diameter or smaller comets
Comet pumps and plates are also used in conjunction with various types of presses to supply the force needed to consolidate the comet composition. Some presses such as arbor presses and bottle jacks (small hydraulic automotive jacks) merely amplify the human power supplied to them and are therefore limited to the amount of force they can apply. Large motorized hydraulic and pneumatic presses are employed when greater speed or production quantities are needed.
Advantages of mechanical pressing:
Very large diameter comets can be produced, from 3" to 6" diameter.
Harder, more consistent comets can be produced when using comet plates.
Shock sensitive comet compositions can be used more safely.
Disadvantages of mechanical pressing:
More expensive equipment requirements
Often requires a dedicated location for setup
Clean up is often more involved
Here is an inexpensive, uncomplicated silver comet that is easy to mix and form into a nice hard comet pellet. It produces a kind of coarse, drippy tail due to the use of the granular aluminum.
|Silver Comet Formula
[Gilliam's notes to the formula above. For the aluminum, try granular aluminum in about 50-150 mesh range, which is what Werner recommends. For mag-al alloy, use -200 mesh. For antimony sulfide, use 200 mesh, Chinese Needle.]
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