Why do candle flames have different colors?

The different colors of candle flames are due to the different temperatures and chemical changes during the combustion process.
A candle flame can be divided into three main areas, and the colors and characteristics of each area are as follows:

1. Flame core (unburned area):
Color: Usually light blue or almost invisible.
Reason: This is the innermost layer of the flame, with the lowest temperature, and the paraffin vapor has not yet fully contacted with oxygen to burn.

2. Inner flame (partially burned area):
Color: Usually yellow or orange-yellow.
Reason: This area is hotter, and the paraffin vapor begins to react with oxygen to burn, but due to incomplete combustion, carbon particles (carbon black) are produced, which glow at high temperatures and appear yellow or orange-yellow. Incomplete combustion is caused by insufficient oxygen supply in this area.

3. Outer flame (completely burned area):
Color: Usually light blue or blue.
Reason: This is the outermost layer of the flame, with the highest temperature, and the most abundant oxygen supply here, and the paraffin vapor can be completely burned to produce carbon dioxide and water vapor. The light emitted by the completely burned area has a shorter wavelength, so it looks light blue or blue.

The change in flame color is affected by a variety of factors:
Completeness of combustion: If the combustion is incomplete, more carbon particles will be produced, resulting in a yellow or orange-yellow flame. If the combustion is complete, a pale blue flame will be produced.
The composition of the candle: Different types of wax (such as paraffin, beeswax, soy wax) and added chemicals will affect the color of the combustion.
The supply of oxygen: The amount of oxygen exposed to the flame will affect the completeness of the combustion. Good ventilation can promote complete combustion and produce a bluer flame.
The material of the candle wick: Different wick materials may affect the color of the flame. For example, a wick containing metal may produce a different color.

Therefore, the color of the candle flame is the result of the combined effect of multiple factors during the combustion process.