A candle is a source of light, and sometimes a source of heat, consisting of a solid block of fuel (commonly wax) and an embedded wick.

Today, most candles are made from paraffin. Candles can also be made from beeswax, soy and other plant waxes, and tallow (a by-product of beef-fat rendering). Gel candles are made from a mixture of paraffin and plastic.

A candle manufacturer is traditionally known as a chandler. Various devices have been invented to hold candles, from simple tabletop candle holders, to elaborate chandeliers.

The heat of the match used to light the candle melts and vaporizes a small amount of fuel. Once vaporized, the fuel combines with oxygen in the atmosphere to form a flame. This flame provides sufficient heat to keep the candle burning via a self-sustaining chain of events: the heat of the flame melts the top of the mass of solid fuel, the liquefied fuel then moves upward through the wick via capillary action, and the liquefied fuel is then vaporized to burn within the candle's flame.

The burning of the fuel takes place in several distinct regions (as evidenced by the various colors that can be seen within the candle's flame). Within the bluer regions, hydrogen is being separated from the fuel and burned to form water vapor. The brighter, yellower part of the flame is the remaining carbon being oxidized to form carbon dioxide.

As the mass of solid fuel is melted and consumed, the candle grows shorter. Portions of the wick that are not evaporating the liquid fuel are consumed in the flame. The incineration of the wick limits the exposed length of the wick, thus maintaining a constant burning temperature and rate of fuel consumption. Some wicks require regular trimming with scissors (or a specialized wick trimmer), usually to about one-quarter inch (~.7 cm), to promote slower, steady burning, and also to prevent smoking.

It is commonly believed that candles made of beeswax burn more cleanly than petroleum-based paraffin waxes. Highly-refined paraffin wax, however, can burn as or more cleanly than natural waxes, creating less particulates during combustion. The type of wick and inclusion of any scents and/or dyes have a much greater impact on the release of compounds, particulates, and smoke, regardless of the base material. The cleanest burning candle will be well-constructed, unscented, undyed, and burn in a draft-free area. A candle will burn well when formulated waxes are blended together (soy, paraffin and other waxes), and fragrance oils and wick selections are balanced properly.

A smoke film can be a concern to those who frequently burn a candle indoors and is also referred to as ghosting, carbon tracking, or carbon tracing. Smoke can be produced when a candle does not burn the wax fuel completely. A scented candle can be a source of candle smoke deposits. Trimming candle wicks to about 6 millimeters (¼ in) or shorter will keep smoking to a minimum. A flickering flame will produce more smoke, therefore a candle should be burned in an area free from drafts.[1]

Differing opinions about which kind of wax in a candle is "natural." Proponents of the soy wax candle will note the material is biodegradable and "all natural." However, most soy beans used in the manufacture of soy wax are genetically modified. Paraffin wax, as used in candle making, is also biodegradable. It also often meets the United States Food and Drug Administration criteria for use in foods and food contact. It has also been claimed that natural waxes have a neutral carbon footprint as carbon dioxide was recently taken from the air to produce the natural wax, which upon burning would not result in a net increase in carbon dioxide.

Color tells us about the temperature of a candle flame. The outer core of the candle flame is light blue -- 1670 K (1400 °C). That is the hottest part of the flame. The color inside the flame becomes yellow, orange and finally red. The further you reach to the center of the flame, the lower the temperature will be. The red portion is around 1070 K (800 °C).

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