This article is from the Pyrotechnics FAQ, by Hans Josef Wagemueller email@example.com with numerous contributions by others.
A star is an amount of pyrotechnic composition that has by some means
been fashioned into a solid object. These are the bright burning objects
you see ejected from Roman candles, shells, mines etc.
Usually the pyrotechnic composition is mixed with a binder and a small
amount of solvent to make a doughy mass which is then fashioned into
stars, although some use has been made of so-called pressed stars, which
involve the composition being pressed extremely hard into a mold with a
hydraulic press or similar, thus doing without the solvent.
The usual methods are to make the composition into a flat pancake or
sausage and cut it up into stars ("cut stars"), pushing it through a tube
with a dowel, cutting it off at regular intervals ("pumped stars") or
rolling cores of lead shot coated in fire clay in a bowl of the
composition ("rolled stars").
Cutting and pumping produce cubic or cylindrical stars, while rolling
produces spherical stars. Pumped stars are the most suitable for Roman
candles, because it is easy to get the correct width. The stars are often
dusted with a primer, usually meal black powder, to ensure ignition.
The shell is a sphere or cylinder of papier mache or plastic which
contains stars and a bursting charge, together with a fuse. It is fired
into the air from a tube using a lift charge, usually black powder. The
time the fuse takes determines the height above the ground at which the
shell will burst, igniting and spreading the stars.
A rocket consists of a tube of rocket fuel, sealed at one end, with a
constriction, or nozzle, at the other end. The burning fuel produces
exhaust gases, which, when forced out the nozzle, produce thrust, moving
the rocket in the other direction.
Solid fuel rockets can be one of two types - end-burning, where the fuel
is solidly packed into the tube, so the fuel can only burn at one end -
and core-burning, where there is a central core longitudinally through
the fuel, so the fuel can burn down its full length. At the top of the
rocket can be a smoke composition, so it is possible to determine the
maximum height ("apogee") of the rocket, or a burst charge and stars.
A lance is a thin paper tube containing a pyrotechnic composition. These
are most commonly used in large numbers to make writing and pictures at
fireworks shows - this is referred to as lancework. The tube is thin so
burns completely away as the lance burns, so as not to restrict light
emission from the burning section.
These are pyrotechnic sprays, often referred to as fountains or flower-
pots. They consist of a tube full of composition, sealed at one end and
with a nozzle at the other, similar to a rocket. Unlike a rocket, they
are not designed to move anywhere, so all the emphasis is on making the
nozzle exhaust as long as pretty as possible, with large amounts of
sparks, nice colours etc.
The sparks are produced by metal powders or coarse charcoal in the gerb
composition, with coarse titanium powder being the chemical of choice.
Gerb compositions in a thin tube set up in a spiral arrangement are used
as wheel drivers, for spinning fireworks e.g. Catherine wheels.
These are similar to gerbs, but usually do not spray as far. They are
usually mounted horizontally in banks of several tubes, placed some
distance above the ground. When ignited, the effect is like a brilliant
waterfall of sparks.
These have a mortar arrangement similar to that for a shell, but are not
designed to send out a shell. The lift charge sends up a bag full of
stars and a bursting charge, with a short fuse set to spread the stars
relatively close to the ground. Because the bag has much less strength
than a shell, the stars are not spread as far, and the final effect is
that of a shower of stars moving upward in an inverted cone formation.