Jessie Taylor
Candles have been used for over two millennia, and while they are no longer necessary for illumination, they are still commonly used for functional, symbolic, and aesthetic purposes. The light from a candle comes from the wax burning. When the wick of a candle is lit, the heat melts and ignites a small amount of solid fuel (the wax), which vaporizes and combines with oxygen in the air to form a flame. Interestingly, the flame is hottest at the bottom, but the wick is hottest at the top, which is why the top of the wick glows. The particles of soot in the flame glow when they are hot, and that is what produces light.
| Characteristics | Values |
|---|---|
| Definition | An ignitable wick embedded in wax or another flammable solid substance such as tallow, that provides light, and in some cases, a fragrance. |
| History | Candles have been used for over two millennia around the world. Primitive oil lamps with lit wicks rested in a pool of oil or fat were used in the Paleolithic period, and pottery and stone lamps from the Neolithic period have been found. Objects resembling candlesticks have been found in Babylonian and middle Minoan cultures, as well as in the tomb of Tutankhamun. |
| Use | Candles were initially used in Christian churches in medieval Europe and later spread to wealthy households. They were a significant form of indoor lighting until the invention of other light sources. Today, candles are used for functional, symbolic, and aesthetic purposes and in specific cultural and religious settings. |
| Composition | Candles are made from wax, which is made of hydrogen and carbon. The wick is typically made of cotton and may be infused with chemicals to modify burning characteristics. |
| Burning Process | When a candle is lit, the heat melts and ignites the wax, which vaporizes and combines with oxygen to form a flame. The flame then melts the top of the wax, which moves upward through the wick and burns. |
| Light Production | The light produced by a candle comes from burning wax. The particles of soot in the flame glow when they are hot (blackbody radiation). |
| Heat Production | The heat produced by a candle comes from burning wax. The wick also burns, but the wax contributes most of the heat. |
| Byproducts | When a candle burns, the hydrogen and carbon in the wax combine with oxygen to form carbon dioxide and water vapour. Small amounts of unburnt carbon molecules contribute to smoke and soot. |
| Health Concerns | Constant exposure to candle particles can lead to cardiovascular and respiratory diseases. Burning candles produce indoor air pollution, and proper ventilation is recommended to minimize exposure. |
| Average Burn Rate | A modern candle typically burns at a steady rate of about 0.1 g/min, releasing heat at roughly 80 W. |
| Luminous Efficacy | The light produced by a candle is about 13 lumens, resulting in a luminous efficacy of about 0.16 lumens per watt. |
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What You'll Learn
The chemical composition of a candle
Wick: The wick of a candle is a crucial component that holds the flame. Commercial candle wicks are typically made from braided cotton, forming a piece of string or cord. The wick's capillarity determines the rate at which the melted wax moves up through the wick to fuel the flame. To modify burning characteristics, wicks are often infused with chemicals. For instance, ammonium nitrate and ammonium sulfate are added to prevent the wick from glowing after the flame is extinguished.
Wax: The wax in a candle serves as the primary fuel source. It is usually made from paraffin wax, derived from petroleum. Paraffin wax is a complex mixture of hydrocarbons, with varying molecular weights and structures that influence the wax's physical properties, such as melting point and hardness. The affordability and versatility of paraffin wax have made it the most commonly used candle wax worldwide. However, other types of waxes, such as beeswax, tallow, soy wax, and palm wax, are also used. The choice of wax affects the candle's burning characteristics, with some waxes offering cleaner burning and eco-friendly alternatives.
Fuel: Candle fuel, often referred to as "wax," can be derived from various sources, including fossil fuels, animal fats, vegetable oils, and waxy substances from insects, plants, and rocks. The development of candle fuels has evolved over time, with early civilizations using tallow rendered from animals, and modern candles utilizing stearin (derived from animal fatty acids) and vegetable-based fuels like soy and palm oils. The fuel in a candle melts and vaporizes when the wick is lit, combining with oxygen in the air to form a flame.
Fragrance and Color: Candles may also contain fragrance and colorant additives. Fragrance materials can be derived from natural essential oils or synthetic aroma chemicals, with over 2,000 options available for candle manufacturers. These additives can alter the chemical composition of the wax, impacting its melting point and combustion characteristics. Similarly, colorants can be added to enhance the candle's appearance.
Burning Process: The chemical composition of a candle determines its burning characteristics. When a candle burns, the wax combines with oxygen to produce carbon dioxide and water vapour. The blue colour in the flame is due to chemiluminescence, while the visible yellow colour comes from radiative emission from hot soot particles. The soot is formed through complex chemical reactions involving fuel molecules and molecular growth, ultimately producing multi-carbon ring compounds.
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How a candle produces light
A candle is an ignitable wick embedded in wax or another flammable solid substance, such as tallow. They have been used for over two millennia and were a significant form of indoor lighting until the invention of other light sources.
When you light a candle, 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 vaporizes the liquid wax (turns it into a hot gas), and starts to break down the hydrocarbons into molecules of hydrogen and carbon. These vaporized molecules are drawn up into the flame, where they react with oxygen from the air to create heat, light, water vapour (H2O) and carbon dioxide (CO2).
The flame also gives off invisible beams of heat in all directions by radiation. The candle continues to "feed" on the wax underneath it until it's all burned away—until all the potential energy locked away in the wax is converted to heat, light, and chemical waste products.
The light and heat from a candle come from the wax burning. The wick, which is typically made of cotton, also burns, although it is the wax that contributes most of the heat. The puddles you sometimes see around the base of a candle are from wax that spilled and dripped down without burning.
The colour of a candle flame depends on the temperature and the presence of soot particles. The blue part of the flame is the hottest, typically reaching 1400°C (2550°F). It is blue because it has an excess of oxygen and burns cleanly. The yellow part of the flame is cooler, at around 1200°C (2190°F). It is yellow because of the presence of soot particles, which glow when they are heated.
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The history of candles
The use of candles dates back to ancient civilizations, where early humans discovered the illuminating properties of fire. One of the earliest known forms of candles was the primitive torch, a bundle of sticks or reeds dipped in animal fat or tallow, providing a rudimentary source of light. The ancient Egyptians are credited with developing some of the earliest candle-like objects, using rushes soaked in animal fat as makeshift torches. Objects resembling candlesticks have also been found in Babylonian and middle Minoan cultures, as well as in the tomb of Tutankhamun.
In the Roman period, candle-making techniques included dipping wicks in molten wax or tallow, shaping wax around a wick, or pouring wax or tallow over the wick. The Romans also introduced molded candles made from tallow or beeswax, which were more consistent in size and shape, making them easier to handle and store. During the Middle Ages, candle-making became an essential trade, with beeswax candles prized for their clean, bright, and sweet-smelling flames. Beeswax candles were primarily used in churches and monasteries, while tallow candles were more affordable and popular among the general population.
In the 18th and 19th centuries, the growth of the whaling industry brought about a significant change in candlemaking. Spermaceti, a wax derived from sperm whale oil, became widely available and was used to create standard candles that burned brighter and didn't produce a repugnant odour. During this period, stearic acid was also discovered, leading to the development of stearin wax, which burned cleanly and was harder and more durable.
In the 20th century, candle-making continued to evolve with the introduction of synthetic waxes, scented candles, and decorative designs. The growth of the U.S. oil and meatpacking industries increased the availability of paraffin and stearic acid, making candles more affordable for the masses. The 1990s witnessed an unprecedented surge in the popularity of candles, with new types of candle waxes being developed, such as soybean wax and palm wax.
Today, candles are still commonly used for functional, symbolic, and aesthetic purposes, playing a significant role in various cultural and religious settings. The evolution of candles mirrors the progress of civilization, and their warm glow continues to bring light, warmth, and comfort to our lives.
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The combustion process of a candle
A candle is an ignitable wick embedded in wax or another flammable solid substance. The combustion process of a candle involves several steps and chemical reactions. Firstly, the wick of the candle is lit, which melts and ignites a small amount of the solid fuel or wax. This molten wax then moves upward through the wick via capillary action. The wick's capillarity determines the rate at which the melted wax travels up the wick. The heat of the flame vaporizes the liquid wax, turning it into a hot gas.
As the wax vapour rises, it combines with oxygen in the air, forming a flame. This flame then melts the top of the solid wax, which continues to fuel the flame and maintain a constant burn. The candle shortens as the wax is consumed, and the wick burns along with it. The light and heat from a candle are produced by the burning of wax. Approximately one-fourth of the energy created by a candle's combustion is radiated as heat, which helps maintain the reaction by melting more wax.
The combustion of wax involves a chemical reaction between the hydrogen and carbon atoms in the wax and the oxygen in the air. This reaction produces carbon dioxide and water vapour. However, candles do not burn perfectly, and unburnt carbon particles, or soot, may escape from the flame as smoke. The yellow portion of the flame is where the smoke is produced, while the blue outer edge is where the wax burns cleanly with oxygen, reaching higher temperatures.
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The health implications of burning candles
Candles have been a significant source of indoor lighting for over two millennia. While electric lights have made candles non-essential, they are still commonly used for functional, symbolic, aesthetic, cultural, and religious purposes.
The therapeutic benefits of burning candles are often considered to outweigh any health risks. However, it is important to understand the potential health implications of burning candles to make informed choices and ensure a safe experience.
Burning candles can release potentially harmful toxins, particulate matter (soot), and volatile organic compounds (VOCs) into the air. Examples of VOCs include formaldehyde and benzene, which are known carcinogens or cancer-causing agents. While the concentrations of these compounds are typically very low, constant exposure to indoor air pollution can lead to potential health risks.
The amount of particulate matter released from burning candles is usually not enough to cause significant health problems in humans, especially when burned in well-ventilated spaces. However, extended exposure to particulate matter can irritate the lungs and potentially lead to cardiovascular and respiratory issues, especially in individuals with pre-existing lung conditions such as asthma or chronic obstructive pulmonary disease.
To minimize the potential health risks associated with burning candles, it is recommended to use higher-quality candles, burn them in well-ventilated spaces, and opt for natural candles made from beeswax, soy wax, or other plant-based waxes. Additionally, following candle safety guidelines is crucial to prevent fire hazards, which pose the most significant danger when burning candles.
In summary, while burning candles can release pollutants and potentially harmful compounds, the current research suggests that the health risks are minimal when candles are used appropriately and in moderation.
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Frequently asked questions
A candle produces light when the wax burns. The flame causes the wax to melt, flow up the wick, and evaporate. The wax vapour then burns, producing light.
The wick of a candle glows because it is hot. The flame is hottest at the bottom, but the wick is hottest at the top. The radiant energy from the flame causes the top of the wick to heat up and start to glow.
Burning candles produce carbon dioxide and water vapour, as well as soot and smoke. Constant exposure to these particles can lead to cardiovascular and respiratory issues. Therefore, it is recommended to ensure proper ventilation when burning candles and to use clean, white candles with fewer additives.
