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Fireworks color
Creating firework colors is a complex endeavor, requiring
considerable art and application of physical science. Excluding
propellants or special effects, the points of light ejected
from fireworks, termed 'stars', generally require an oxygen-producer,
fuel, binder (to keep everything where it needs to be), and
color producer. There are two main mechanisms of color production
in fireworks, incandescence and luminescence.
Incandescence
Incandescence is light produced from heat. Heat causes a
substance to become hot and glow, initially emitting infrared,
then red, orange, yellow, and white light as it becomes increasingly
hotter. When the temperature of a firework is controlled,
the glow of components, such as charcoal, can be manipulated
to be the desired color (temperature) at the proper time.
Metals, such as aluminum, magnesium, and titanium, burn very
brightly and are useful for increasing the temperature of
the firework.
Luminescence
Luminescence is light produced using energy sources other
than heat. Sometimes luminescence is called 'cold light',
because it can occur at room temperature and cooler temperatures.
To produce luminescence, energy is absorbed by an electron
of an atom or molecule, causing it to become excited, but
unstable. When the electron returns to a lower energy state
the energy is released in the form of a photon (light). The
energy of the photon determines its wavelength or color.
Sometimes the salts needed to produce the desired color are
unstable. Barium chloride (green) is unstable at room temperatures,
so barium must be combined with a more stable compound (e.g.,
chlorinated rubber). In this case, the chlorine is released
in the heat of the burning of the pyrotechnic composition,
to then form barium chloride and produce the green color.
Copper chloride (blue), on the other hand, is unstable at
high temperatures, so the firework cannot get too hot, yet
must be bright enough to be seen.
Quality
Pure colors require pure ingredients. Even trace amounts
of sodium impurities (yellow-orange) are sufficient to overpower
or alter other colors. Careful formulation is required so
that too much smoke or residue doesn't mask the color. With
fireworks, as with other things, cost often relates to quality.
Skill of the manufacturer and date the firework was produced
greatly affect the final display (or lack thereof).
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