Spark (fire)

A spark is an incandescent particle. Such sparks may be produced by pyrotechnics, by metalworking or as a by-product of fires, especially when burning wood.

In pyrotechnics, iron filings and metal alloys such as magnalium may be used to create sparks. The quantity and style of sparks produced depends on the composition and pyrophoricity of the metal and can be used to identify the type of metal by spark testing. In the case of iron, the presence of carbon is required, as in carbon steel — about 0.7% is best for large sparks. The carbon burns explosively in the hot iron and this produces pretty, branching sparks. The color of sparks used in pyrotechnics is determined by the material that the sparks are made from, with the possibility of adding different chemical compounds to certain materials to further influence the color of the sparks. The duration of the existence of a spark is determined by the initial size of the particle, with a larger size leading to a longer-lasting spark.

Metals with low thermal conductivity are especially good at producing sparks. Titanium and zirconium are especially good in this respect and so are now used in fireworks. Copper, on the other hand, has a high conductivity and so is poor at producing sparks. For this reason, alloys of copper such as beryllium bronze are used to make safety tools which will not spark so easily.

Robert Hooke studied the sparks created by striking a piece of flint and steel together. He found that the sparks were usually particles of the steel which had become red hot and so melted into globules. These sparks can be used to ignite tinder and so start a fire.

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