Jessie Taylor
Candles are a leading cause of residential fires in the United States, according to the National Fire Protection Association, but have you ever wondered what happens to a candle as it burns down? Where does all of that wax go? The basic structure of a candle is simply wick and wax. When you light a candle, the heat from the flame melts the wax near the wick, which is then drawn up the wick by capillary action. The flame vaporizes the liquid wax, turning it into a hot gas, and starts to break down the hydrocarbons into molecules of hydrogen and carbon. These vaporized molecules are then drawn up into the flame, where they react with oxygen from the air to create heat, light, water vapour, and carbon dioxide.
| Characteristics | Values |
|---|---|
| Candle structure | Basic, made of wick and wax |
| Candle composition | Hydrogen and carbon atoms (hydrocarbons) |
| Candle burning | The heat of the flame melts the wax near the wick, which is then drawn up the wick by capillary action |
| Flame formation | The flame vaporizes the liquid wax, breaking down the hydrocarbons into molecules of hydrogen and carbon, which react with oxygen from the air to create heat, light, water vapour, and carbon dioxide |
| Flame shape | Elongated or teardrop due to convection currents |
| Burn rate | The amount of wax consumed per hour, typically measured in grams per hour (g/h) |
| Afterglow | The light emitted after the removal of an energy source, causing the wick to glow and burn down slightly |
| Mushrooming | Small amounts of carbon at the top of the wick due to incomplete combustion |
| Soot | Unburned carbon particles that escape from the flame due to incomplete combustion |
| Candle safety | Use a candle snuffer instead of blowing directly on the flame to avoid splashed wax and burns |
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What You'll Learn
The wax melts and moves up the wick
When a candle is lit, the heat from the flame melts the wax near the wick. This liquid wax is then drawn up the wick by capillary action. The heat of the flame vaporizes the liquid wax, turning it into a hot gas. The vaporized molecules are then drawn up into the flame, where they react with oxygen from the air to create heat, light, water vapour, and carbon dioxide.
As the liquid wax moves up the wick, the candle becomes shorter. The end of the wick bends and is consumed in the flame. This incineration of the wick limits the length of the exposed portion of the wick, thus maintaining a constant burning temperature and rate of fuel consumption.
The blue area at the base of the flame is the hottest part, typically reaching 1400° C (2552° F). It is blue because it directly meets with the oxygen in the air. Above this is a small dark orange-brown section, where various forms of carbon continue to break down and small, hardened carbon particles start to form. As they rise, they are heated to approximately 1000° C.
At the bottom of the yellow zone, the formation of carbon (soot) particles increases. As they rise, they continue to heat up until they ignite and emit light. Because the yellow portion of the spectrum is the most dominant when the carbon ignites, the human eye perceives the flame as yellowish.
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The wax vapourises and combines with oxygen
When a candle burns, the heat of the flame melts the wax near the wick. This liquid wax is then drawn up the wick by capillary action. The heat of the flame then vaporises the liquid wax, turning it into a hot gas. The wax vapour combines with oxygen in the atmosphere to ignite and form a constant flame. This flame provides sufficient heat to keep the candle burning.
The oxygen-rich blue zone at the base of the flame is the hottest part, typically reaching 1400° C (2552° F). It is here that the hydrocarbon molecules in the wax vapour start to break apart into hydrogen and carbon atoms. The hydrogen and carbon atoms then react with oxygen from the air to create heat, light, water vapour (H2O), and carbon dioxide (CO2).
As the wax is melted and burned, the candle becomes shorter. The end of the wick bends and is consumed in the flame. The incineration of the wick limits the length of the exposed portion of the wick, thus maintaining a constant burning temperature and rate of fuel consumption.
The warm air moving up from the flame creates a convection current, causing cooler air and oxygen to rush in at the bottom of the flame to replace it. This cycle of upward-moving air gives the flame its elongated or teardrop shape.
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The carbon and hydrogen atoms split
When a candle burns, the heat from the flame melts the wax near the wick. This liquid wax is then drawn up the wick by capillary action. The heat of the flame vaporizes the liquid wax, turning it into a hot gas.
The oxygen-rich blue zone at the base of the flame is where the hydrocarbon molecules start to break apart into hydrogen and carbon atoms. These vaporized molecules are then drawn up into the flame, where they react with oxygen from the air to create heat, light, water vapour, and carbon dioxide.
The dark orange/brown region above the blue zone has relatively little oxygen. This is where the various forms of carbon continue to break down and small, hardened carbon particles (soot) begin to form. As they rise, along with the water vapour and carbon dioxide, they are heated to approximately 1000 degrees Celsius.
At the bottom of the yellow zone, the formation of soot particles increases. As they rise, they continue to heat up until they ignite and emit a full spectrum of visible light. The yellow portion of the spectrum is the most dominant when the carbon ignites, which is why the human eye perceives the flame as yellowish.
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The wick incinerates itself
The wick of a candle is an essential component, enabling the candle to burn and produce light and heat. The wick is responsible for drawing up the liquefied wax, which then vaporizes and combines with oxygen to create a flame. As the candle burns, the wick gradually shortens, and in modern candles, the end of the wick bends and is consumed by the flame through incineration.
The process of wick incineration is a crucial aspect of candle burning. When a candle is lit, the heat from the flame melts the wax near the wick. This liquid wax is then absorbed by the wick and moves upward through a process called capillary action. As the wax reaches the flame, it vaporizes and combines with oxygen, leading to combustion.
The incineration of the wick occurs when the exposed portion of the wick bends and is consumed by the flame. This self-trimming mechanism helps maintain a constant burning temperature and rate of fuel consumption. Without this self-trimming feature, wicks would require regular trimming with scissors or specialized wick trimmers to prevent smoking and promote steady burning.
The incineration of the wick is a result of the heat and flame produced by the candle. As the wax is consumed and the candle shortens, the wick gradually moves downward, closer to the flame. Eventually, the end of the wick reaches the flame and is incinerated, or burned, in the process.
The wick's incineration marks the end of the candle's life. Once the wick is consumed, the candle can no longer sustain the flame, and the burning process comes to a halt. At this point, all that remains of the candle is the residual wax and the incinerated wick, which may appear as a small, dark residue.
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The candle shortens
The rate at which a candle burns is known as the burn rate, which is typically measured in grams of wax consumed per hour. The burn rate of a candle can be calculated by weighing the candle at the start and end of a burning period and dividing the difference in weight by the number of hours the candle has burned. This calculation gives the burn rate in grams per hour.
As the candle burns, the end of the wick bends and is consumed in the flame, which limits the length of the exposed portion of the wick. This self-trimming action helps to maintain a constant burning temperature and rate of fuel consumption. In pre-19th-century candles, the wicks required regular trimming with scissors or "snuffers" to prevent smoking and promote steady burning.
The shape of a candle flame is teardrop-shaped due to the convection current created by the rising warm air and the cooler air and oxygen rushing in at the bottom of the flame to replace it. The blue base of the flame is the hottest part, reaching temperatures of up to 1400°C, where the oxygen-rich environment causes the hydrocarbon molecules to vaporize and break apart into hydrogen and carbon atoms. Above this is a small dark orange-brown section, where carbon particles continue to break down and form soot. As these particles rise, they heat up to around 1000°C and eventually ignite, emitting a full spectrum of visible light. The yellow portion of the spectrum is the most dominant, giving the candle flame its characteristic yellowish colour.
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Frequently asked questions
The wax is melted and burned, causing the candle to shorten. The liquid wax is drawn up the wick by capillary action and vaporized, turning into a hot gas. The wax eventually evaporates.
The end of the wick bends and gets consumed in the flame. Modern wicks are constructed in a way that allows them to trim themselves through incineration by fire.
The flame will go out once the fuel is used up or the heat is eliminated. The flame can also be extinguished using a candle snuffer, which is usually a small metal cup at the end of a long handle.
The container may contain residual wax, which can be reused or recycled. It is important to dispose of the container properly, especially if it is made of glass or another breakable material.
