Sunday, 8 November 2009

Sheppey Rugby Club Fireworks Display, 7th Nov 2009

A firework is a low explosive pyrotechnic device used primarily for aesthetic and entertainment purposes. The most common use of a firework is as part of a fireworks display. A fireworks event (also called a fireworks show or pyrotechnics) is a display of the effects produced by firework devices. Fireworks competitions are also regularly held at a number of places. Fireworks (devices) take many forms to produce the four primary effects: noise, light, smoke, and floating materials (confetti for example). They may be designed to burn with coloured flames and sparks including red, orange, yellow, green, blue, purple, and silver. Displays are common throughout the world and are the focal point of many cultural and religious celebrations.

Fireworks were invented in ancient China in the 12th century to scare away evil spirits, as a natural extension of the Chinese invention of gunpowder. Such important events and festivities as Chinese New Year and the Mid-Autumn Moon Festival were and still are times when fireworks are guaranteed sights. China is the largest manufacturer and exporter of fireworks in the world.

Fireworks are generally classified as to where they perform, either as a ground or aerial firework. In the latter case they may provide their own propulsion (skyrocket) or be shot into the air by a mortar (aerial shell).

The most common feature of fireworks is a paper or pasteboard tube or casing filled with the combustible material, often pyrotechnic stars. A number of these tubes or cases are often combined so as to make, when kindled, a great variety of sparkling shapes, often variously coloured. The skyrocket is a common form of firework, although the first skyrockets were used in war. The aerial shell, however, is the backbone of today's commercial aerial display, and a smaller version for consumer use is known as the festival ball in the United States. Such rocket technology has also been used for the delivery of mail by rocket and is used as propulsion for most model rockets.

Colours in fireworks are usually generated by pyrotechnic stars—usually just called stars—which produce intense light when ignited. Stars contain five basic types of ingredients.

§  fuel which allows the star to burn
§  An oxidizer—a compound which produces (usually) oxygen to support the combustion of the fuel
§  Colour-producing chemicals
§  binder which holds the pellet together.
§  Chlorine Donor which provides chlorine to strengthen the colour of the flame. Sometimes the oxidizer can serve this purpose.

Some of the more common colour-producing compounds are tabulated here. The colour of a compound in a firework will be the same as its colour in a flame test (shown at right). Not all compounds that produce a coloured flame are appropriate for colouring fireworks, however. Ideal colorants will produce a pure, intense colour when present in moderate concentration.

Example compounds
Strontium (intense red)
Lithium (medium red)
Copper halides
CuCl2 (copper chloride), at low temperature
Rubidium (violet-red)

The brightest stars, often called Mag Stars, are fuelled by aluminiumMagnesium is rarely used in the fireworks industry due to its lack of ability to form a protective oxide layer. Often an alloy of both metals called magnalium is used.

Many of the chemicals used in the manufacture of fireworks are non-toxic, while many more have some degree of toxicity, can cause skin sensitivity, or exist in dust form and are thereby inhalation hazards. Still others are poisons if directly ingested or inhaled.

 Photograph Details: Nikon D40, Focal Length 82mm, ISO-200, exp: 1/3 sec, exposure bias: -1.7, F-stop f/4

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