The first job a pyrotechnician has after planning the show is building the actual aerial shells that will be used. This is a very involved and time consuming process, but it is crucial to the end result that the spectators will take in. Packing the shells carefully will insure that there are no embarrassing dead shells during the show, and that the shell bursts will be as brilliant as possible.
Each type of shell is available in the following sizes: 2" through 6", 8", 10", 12", 16", 24", and 36". Sizes from 16 inches on up are only used during very large scale shows as they are extremely expensive and require a huge safe zone to fire from. The difference between cylinder and ball shell types is basically a price/performance one. Ball shells are easier to manufacture, but aren't capable of carrying as many burst stars as cylinder style shells of the same dimensions. Cylinder style shells are more expensive, but as I mentioned are much more colorful and impressive.
Now we will go through an abbreviated process of constructing a spherical aerial shell. The first step is to make a form to be used to construct the shell around. Some pyrotechnicians use Styrofoam balls for this because they are easy to shave down to the appropriate size for the shells they are trying to make. It is very important to shave off some of the form because it needs to be smaller than the expected shell size to allow for the build up of paper around it. Then a thin layer of plastic is fitted around the form so that the shell paper won't stick to it. This enables the forms to be used more than once. The next step is to apply the actual shell material around the form. Most pyrotechnicians use newspaper to do this. They basically cut the newspaper into thin strips and paste it around the form with either Elmer's glue or wheat paste. The larger the shell, the more layers of newspaper that are required. The process is somewhat like working with plaster of Paris. Once the form is covered with appropriate number of layers it is placed in an oven for three or four hours for drying.
After the shells are dried they must be cut in half for the loading of the stars. To do this many pyrotechnicians use a wood lathe with an attached face plate that is normally used for creating wooden bowls. However, before using the lathe, an adapter for the wood lathe must be constructed so that the face plate will accept the curvature of the dried sphere. This is done by making a circular depression in a piece of soft wood big enough to hold part of the sphere. Next the paper shell is put into the wood adapter and fastened up against the faceplate for use on the lathe. The lathe is turned on and used to rotate the sphere while the operator cuts the sphere with a utility knife positioned on the tool rest. Once the sphere is cut in half it can then be loaded with the burst stars and pasted back together for firing. That is all there is to it!
We hope this page gives you a little insight as to what kind of work goes into constructing the shells fired at your local fireworks shows. Please visit our other topic specific pages to find out more about the entire pyrotechnic process, and then feel free to apply your knowledge to our interactive page.
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