We have seen flames of different colors: burning firewood in the fireplace has yellow, orange, red, white and blue flames. The color of the flame depends on two factors: the temperature of the fire and the substance that burns.
In order to understand the relationship between temperature and color, let us first look at the electric stove. The coil on the electric stove is cold and black before power is applied. Now suppose you want to burn the soup. When you turn on the electric stove, the coil starts to heat up and slowly turns dark red. As the coil temperature gets higher and higher, it also becomes more and more red. Finally, when the maximum temperature is reached, the coil turns into a bright orange-red color.
Of course, the electric furnace itself does not burn, nor the coils are on fire, they are just getting hotter. If their temperature can be heated higher, their color changes may be more pronounced, they will turn yellow, then white, then blue, instead of keeping orange red. Blue actually indicates the highest temperature.
The principle of the color of the flame is similar to the above. For example, the flame of a candle is used. During the burning process, the flame has several colors.
The process of combustion requires oxygen. If a small jar is placed over the flame, the flame will be extinguished due to lack of oxygen. Therefore, when the candle is burned, the position of the flame near the bottom is darker due to less oxygen. Oxygen is more abundant at the outer edge of the flame, so the fire is strong and the color is brightest. As the burning wick becomes shorter and shorter, the wax melts, the particles splatter, and tiny carbon particles fly, and these materials are burned into tiny pieces of carbon, which then fly with the flame. It’s very hot, it’s hot enough to shine, just like the coil on the electric furnace turns red.
In fact, the temperature of these carbon particles is higher than the coils on the electric furnace, so they do not emit red light but emit yellow light. This is also the reason why most of the candle flame is yellow. Near the wick, the flame is blue because the temperature here is higher.
We can see more colors in the flames or bonfires in the fireplace. Firewood is cooler than candle flames, so it looks more orange. But the reason we can see the yellow color is because some of the carbon particles, which are very hot, will appear yellow. The black smoke in the chimney is what the carbon particles look like after cooling.
Certain chemical components in burning wood also produce different colors. For example, there will be some sodium in the fire (this is part of the salt we eat every day), which glows bright yellow when heated. There may also be calcium in the flame (we all know that there is a lot of calcium in the milk), and the calcium emits a deep red light when heated. In addition, if there is phosphorus in the fire, there will be green light. These elements may be found in burning wood or other burning materials, so the firewood has more types of colors.
Finally, all these colors can be mixed to form white light, just as the rainbow’s seven-color light mixes to turn white.