Whether a burning candle changes color is a common question for those interested in how candles work. The short answer is that yes, a candle flame can change color during the burning process due to a few different factors.
What Determines a Candle’s Flame Color?
The color of a candle’s flame is primarily determined by two things:
- The candle’s wax composition
- The temperature of the flame
Most standard candles are made from paraffin wax, a byproduct of petroleum refining. Paraffin wax burns cleanly, which results in a yellow/orange colored flame. The yellow/orange color is a result of carbon molecules in the wax cracking and releasing energy as visible light.
However, there are other types of waxes that can produce different flame colors. Beeswax, for example, contains more carbon atoms than paraffin wax, which causes it to burn with more of a bright yellow color. Soy wax contains less carbon, resulting in more of a yellow-white colored flame.
The temperature of the candle flame also impacts its color. Hotter flames tend to burn blue or white, while cooler flames appear more yellow or orange. As a candle burns down, the flame gets smaller and cooler, which can make it appear more yellow than when it was a larger, hotter flame.
Why Does a Candle Flame Change Color When Burning?
There are a few reasons why a candle’s flame may change color during the burning process:
- Wax pool temperature – As the melted wax pool gets hotter, the flame gets hotter and burns bluer.
- Flame size – A smaller flame is usually cooler and more yellow/orange.
- Wick issues – Soot buildup on the wick can cool the flame and make it more orange. Trimming the wick helps keep the flame hot and blue.
- Wax additives – Some candlemakers add dyes and scents to their wax blend, which can impact flame color.
- Air currents – Breezes or drafts that disturb the flame can make it burn cooler and more yellow.
So in summary, as the candle burns, the wax pool temperature, flame size, wick condition, and other factors may alter the color slightly back and forth between yellow and blue. But in general, the flame often gets smaller and more yellow as the candle extinguishes.
What Causes a Candle Flame to Burn Different Colors?
Some of the main factors that can cause a candle flame to burn colors besides yellow/orange include:
- Blue color – A hotter, bluer flame is typically a result of a higher wax pool temperature. It can also be caused by a bigger wick or higher stearin content in the wax, both of which increase the flame temperature.
- Yellow color – A cooler, more yellow flame is often caused by a lower temperature, smaller flame size, breeze/drafts, or soot buildup on the wick.
- Green color – Green flames are created by adding boron compounds to the candle wax. The boron provides the green color.
- Red/Orange/Purple colors – Various brighter colors can be created by adding special dyes and salts to the wax, such as sodium, lithium, or potassium compounds.
So by carefully selecting specific waxes, wick types, and additives, candlemakers can create flames that burn in an array of vivid colors. But in a normal candle with no dyes, the color varies naturally based on temperature and other factors.
Does Burning Candle Wax Decompose?
Yes, burning a candle does gradually decompose the wax over time through the chemical process of combustion. Specifically:
- The heat of the flame melts the solid wax into a liquid state in the wax pool.
- The liquid wax moves up the wick via capillary action.
- The liquid wax is vaporized at the flame and broken down into smaller hydrocarbon molecules in a gas/vapor state.
- The hydrocarbon vapors react with oxygen and combust, giving off heat, light, water vapor, and carbon dioxide.
- The decomposition process continues progressively until all of the wax is used up and no liquid remains in the candle.
So in summary, the heat and chemical reaction of combustion does indeed decompose and break down solid candle wax into byproducts like water vapor and CO2. This is why the candle gets shorter and shorter as it burns – the wax is literally being chemically decomposed by the flame.
What Causes Candle Wax to Decompose When Burning?
There are two primary causes of candle wax decomposing when burned:
- Heat: The heat of the candle flame melts solid wax into a liquid state so it can travel up the wick. Heat is also necessary to vaporize the liquid wax molecules into a gaseous state prior to combustion.
- Oxidation: The chemical reaction of the vaporized wax with oxygen (O2) is an oxidation reaction. The hydrocarbon molecules combine with oxygen atoms, releasing energy in the form of heat and light. This oxidizing reaction decomposes the wax’s molecular structure.
So in summary, it is the combination of heat energy plus an oxidative chemical reaction with oxygen that causes the candle wax molecules to break down and decompose as the candle burns.
What Are the Steps of Candle Wax Decomposition?
Here are the key steps in the process of a candle burning and wax decomposition:
- Solid wax melts into a liquid state in the melted wax pool, due to heat transfer from the flame.
- Liquid wax moves up the wick via capillary action.
- Liquid wax vaporizes at the flame into a gaseous hydrocarbon vapor.
- Vaporized hydrocarbons react with oxygen in an exothermic oxidation reaction.
- The combustion reaction gives off energy as heat and light (visible to the eye as the flame).
- The oxidized wax molecules decompose into smaller byproducts like water vapor and carbon dioxide.
- The decomposition process continues, using up the liquid wax, until no fuel remains and the flame goes out.
The chemical decomposition of wax therefore occurs in an ongoing progression as the candle burns down. The wax transitions from solid, to liquid, to gas, then finally decomposes via the combustion process.
How Does Candle Wick Play a Role?
The wick plays several key roles in facilitating wax decomposition and the candle burning process:
- Wicks are made of braided fabric that provide capillary action to draw liquid wax up towards the flame.
- Wicks insulate and help regulate heat flow to maintain an even burn.
- Wicks have a large surface area to allow liquid wax to vaporize more readily.
- Wicks provide initial fuel to help light and establish the flame upon first being lit.
- Wicks should curl to present new fresh wick to the flame as it burns.
So in summary, the capillary behavior, texture, and combustion properties of the wick make it an essential component in facilitating wax decomposition and sustaining the candle flame.
How Does Candle Wick Composition Impact Burning?
Candle wicks are typically made from materials like cotton, paper, or fiberglass. The composition impacts burning performance in a few key ways:
| Wick Material | Properties | Effects on Burning |
|---|---|---|
| Cotton | Natural fibers, absorbent | Provides excellent capillary action for wax pool |
| Paper | Tightly rolled paper | Channeles wax similar to cotton |
| Fiberglass | Stiffer interwoven glass fibers | Less flexibility but resist burning up |
So the wick material affects wax pooling, rigidity, and burn-up resistance. Cotton and paper tend to be good at drawing wax, but may need to be trimmed more as they burn. Fiberglass wicks are more durable and low-maintenance.
How Does Candle Wick Thickness Affect Flame?
Thicker wicks typically create a larger, hotter candle flame. Thinner wicks create a smaller, cooler flame. This is because wick thickness impacts a few key properties:
- Wax delivery – Thicker wicks allow more liquid wax to travel up for burning.
- Fuel supply – More wax creates a larger, hotter flame since there is more fuel.
- Melt pool – Thicker wicks heat and melt more wax to sustain the flame.
- Surface area – A thicker wick provides more surface for wax vaporization.
However, an oversized wick can get out of control and cause blowouts, flaring, sooting, or excess smoke. That’s why it’s important to pair the proper wick thickness to the wax composition and candle diameter.
Do Candle Additives Change the Flame?
Yes, certain additives mixed into the candle wax can definitely impact the flame’s size, color, and burn properties. Some examples include:
- Dyes – Colored dyes make the flame brighter and tinted to match the dye color.
- Fragrances – Scents may make the flame sputter from oils vaporizing.
- Stearin – Added stearin makes a hotter, brighter flame.
- Vybar – This wax additive makes the flame harder to extinguish.
- Palm wax – Adds a soft, bright glow with little sooting.
Candlemakers have to test waxes and formulation ratios meticulously to find the right balance of additives. Too much of certain additives can cause an uncontrolled flame or even a potential fire hazard.
What Are Signs of Improper Candle Burning?
Some signs that a candle may be burning improperly, with potential issues related to the wax, wick, or other factors, include:
- Flickering, jumping flame
- Mushrooming or flattened wick top
- Excess smoke or soot
- Small, low flame
- Very tall, roaring flame
- Wax pooling improperly
- Burning too quickly
- Residue buildup on glass or surface
Candle issues like these are often caused by an improper wax-to-wick ratio, clogged or oversized wick, drafts, or other environmental factors. Paying attention and trimming the wick can help improve some burning problems.
How Does Air Temperature Affect Candles?
The surrounding air temperature can definitely impact how well a candle burns. Here are some effects of air temperature on candles:
- Hotter air heats the wax pool more, making the flame burn hotter and faster.
- Cooler air may create a taller flame as it draws more for heat.
- Breezes or drafts in the air make the flame flicker and dance.
- Very cold air can cause the wax to solidify too quickly and clog the wick.
- A cold or drafty room may hinder wax pooling and lead to tunneling.
- Excessive heat can cause the candle to burn down dangerously fast.
For best results, most candle manufacturers recommend burning candles in room temperatures of around 60-80°F. Avoiding drafts and burning in very cold or hot rooms can prevent issues.
Why Should You Trim the Wick?
Trimming the wick to about 1/4″ before each lighting is recommended for a few reasons:
- Creates an even, steady flame right away.
- Removes any mushrooming or residue buildup.
- Allows the wax to pool and melt properly.
- Prevents smoking, flaring, or a wick that is too short.
- Minimizes excess soot on the glass and walls.
- Reduces risk of commission and improves safety.
Wicks should be trimmed every few hours as the wax burns down. Long wicks start to curl over, drown in wax, and darken the wax pool. Trimming improves the look and performance.
What Causes Candles to Tunnel or Sink?
Tunneling, where wax melts in a deep ring around the edge but leaves a sinkhole in the center, is typically caused by one of these issues:
- Wick is too small for the wax or jar – Upgrade to a bigger wick.
- Cold spots and drafts – Move candle away from vents or windows.
- Burning in a cold room – Burn at 60-80°F for best pooling.
- Wick trimmings fell into wax – Remove debris for even melting.
- Old or low-quality wicks – May need thicker, better quality wicks.
Fixing tunneling often requires switching to a larger diameter or braided wick. Wicks that are pressed flat work better than round wicks to create even melt pools.
Conclusion
The color and behavior of a candle’s flame can vary across the burn time based on wax composition, wick issues, temperature changes, and other factors. While a typical paraffin wax candle burns yellow and orange, other additives and dyes can create more vivid red, blue, or rainbow flames. Paying attention to the flame and making wick adjustments is key to addressing common candle issues like tunneling or sooting.