See how professional pyrotechnicians prepare a large firework display.

The fiery bursts in the sky in most firework displays are from AERIAL SHELLS. They are NOT rockets. A black gunpowder propelling charge under the shells causes them to rise high into the air before presenting their colorful magic. Most Asian countries manufacture ROUND SHELLS. These 12 and 10 inch (300 and 250 mm) diameter round shells your host is holding are larger than those used in most firework displays.

Many non-Asian countries, including the United States, mainly produce CYLINDRICAL SHELLS. These have the ability to be made as long as desired, in order to contain more color material or to produce multiple presentations. They produce a more random pattern of fire in the sky than round shells. This 13 inch ( 325 mm) long shell produces two "breaks" of color and then a loud report (bang).
Another mortar-fired effect used in displays is the firework MINE. The colors from those are thrown up into the air already burning. In aerial shells the effects do not ignite until they reach altitude. Both shells and mines use STARS, the pellets of combustible material seen in this photo of a four-inch (100 mm) diameter mine. The top has been removed for this photo.
All shells and mines are fired from MORTARS. They are normally buried three quarters of their length in the ground, but may be placed in barrels full of earth, or mounted in freestanding racks. Mortars can be made from steel, plastic, fiberglass or paper tubing. Plastic mortars are replacing these steel ones in many displays now.
The MAIN MORTAR LINE will contain individual mortars for each shell in the display, if the show is to be electrically fired. A "hand fired" show usually contains many fewer mortars because they will be reloaded during the show. Due to the location requirements, these mortars could not be buried in the ground.
This close-up of a firework display firing area shows 4 through 6 inch (100 to 150 mm) display shells waiting to be loaded into plastic mortars. These shells are what make the beautiful patterns of fire in the sky at countless displays each year.
When ready to fire, the main display area will look something like the image to the left. This electrically fired show contains approximately 500 mortars and shells.
Firework displays may also be fired from specially designed trailers. They are especially useful in areas where it is impossible to bury mortars or when a show must be prepared with short notice. Atlas Enterprises helped pioneer the use of custom designed trailers for firework displays.
The FINALE is usually fired from above-ground racks and will propel a large number of shells into the sky in a very short time. Many finales feature 3 inch  (75 mm) shells like those your host is loading here. These are paper mortars. I have been notified of an electric match ignited by the static electric charge generated by the type of plastic chairs shown here. I now recommend plastic chairs NOT be used at display sites during show preparation.
This is a 250 shot FINALE for a very large firework display. It has shells from 3 inches to 6 inches (75 to 150 mm) in diameter.
Some displays have frame-mounted "set pieces" of various items such as flags. This is what an American Flag set piece looks like during day time.
Large repeating display "cakes" are more popular every year. As a result, many new varieties of shell, comet, report and mixed cakes become available each year. This box is approximately one by two feet in size. (300 by 600 mm.)
2-inch (50 millimeter) diameter Roman candles are a very showy part of pro displays too. These tubes are approximately 36 inches (900 mm) tall. Large Roman candles are quite popular in displays now.
LOW LEVEL EFFECTS such as Roman candle batteries, fountains, comets and small display mines can be mounted on special boards, racks or poles.