The Chemistry Behind Candles
Tuesday, April 10, 2018
Edit
Image source: http://www.digitaljournal.com/img/2/2/5/4/i/4/1/3/o/1847107465_e42e7f7fd3greenfireworks.jpg
For such a simple thing, there is actually a lot of science going on inside a candle. What makes a candle a candle are essentially three things: a wick, which feeds fuel, wax, into a flame: three everyday things that make a candle a sophisticated combustion device that burns the very form its fuel--wax, takes.
Let's take it an element at a time.
Scientists define wax as a material that is a 'solid' at room temperature which turns to 'liquid' at a higher temperature. It is smooth, slightly pliable, has a low odor, is water repellent and has a low toxicity. Candlemaking waxes are primarily hydrocarbons, which, in chemistry, are simple organic compounds made up of hydrogen and carbon atoms and which are one of the Earth's major sources of energy.
Candlemaking waxes are derived from various substances. In the early days, animal fat, seeds, insects, beehives and other plants were used as sources for combustible candlemaking wax. A popular candlemaking wax that dates back to the first millennium is beeswax. One of the most common candlemaking waxes, paraffin, was discovered in the 1800s by French chemists. Paraffin was long touted as being the most efficient, economical and easily obtainable type of candlemaking wax.
Today, however, there is growing interest in plant and vegetable-based candlemaking waxes that come from sustainable, cost effective, environment friendly sources, which are biodegradable and all-natural. While beeswax still belongs in that category, it is scarce and the wax is difficult to obtain, making it quite expensive. Inventors and candle makers have recently discovered that first soybean wax, and now palm wax, make excellent waxes especially for premium candles.
What a wick does is primarily to bring up fuel to the flame. It acts like a fuel pump which draws the melted wax into the burning flame. For many people, the candle wick is something that is taken for granted. We are usually more interested in the candlemaking wax - what color it is, how it smells like, what it's made of. What we don't know is that the wick's size, shape and material matter too, otherwise a candle will not work properly.
Wicks are usually made of fibers that are twisted, braided or knitted together. A majority of wicks manufactured in the United States are usually made wholly of cotton or cotton-paper combinations. There are some which are composed of some type of metal and paper. What wicks are NOT made of today is lead which was banned in the U.S. in 2003. Wicks are always matched to the amount, color, fragrance and type of wax of a candle. The right wick ensures that the burning requirements of the candle are met and that the candle will burn as it should. The correct wick will slowly and consistently feed the wax into the flame. The shape of the wick also makes a big difference.
Different wick shapes are appropriate for different types of candles. Flat wicks are commonly used in taper or pillar candles, while square wicks are appropriate for beeswax candles. Cored wicks are called such because within the fibers, there is usually another material embedded to stiffen the wick. These are often cotton, paper, zinc or tin. Cored wicks are commonly used in candles in containers and votives.
Lighting a candle melts the wax around the wick. The wick then pulls up the melted wax into the flame through a phenomenon called capillary action. Capillary action, or capillarity, refers to the way liquid, in a candle's case liquefied wax, tends to move "up-hill" or against the flow of gravity. Once pulled up, the wax is turned into gas by the heat of the flame. This is where the hydrogen and carbon (remember hydrocarbons?) molecules in the gas react with oxygen to create light and heat, releasing water vapor and carbon dioxide. This whole process is called combustion. The candle continually combusts through the cycle of the flame heating more wax which is drawn up the wick to make more flame until all the fuel, wax, has been used up or the candle is extinguished.
Most of today's consumers don't buy candles for lighting purposes. Candles are purchased for their quality, attractiveness and, most of all, fragrance. However, even these "add-ons" have to be carefully selected so that they don't impede the efficient burning of a candle. Candle-makers can choose from more than 2,000 fragrance oils and chemicals to scent their candles. United States industry standards dictate that these oils and chemicals must be appropriate to use with candles, meet safety standards and are not hazardous to people's health.
Just like in recent candle wax trends, there is increased demand for fragrances that are promoted as natural and safe. Consumers usually expect that a candle's color embodies its fragrance. For instance, a raspberry scented candle is expected to be reddish while jasmine ones are supposed to be white.
In their raw form, though, candlemaking waxes are usually white like soy wax, palm wax and paraffin or yellowish like beeswax. Beeswax candles are usually presented in their natural color but there are a myriad of options for soy, palm and paraffin. While colors do make candles attractive, colorants, like fragrances, are suitable for candle use and are safe to burn. And, like wicks, the right kind and amount of pigment used in a candle varies depending on the type of wax, wick and fragrance used in making the candle.
Wax and candlemaking is an age old tradition. Many of us enjoy candles on a daily basis without realizing all the processes, materials and innovation that goes into each one. Then again, informing ourselves may help us appreciate that the true beauty of a candle is that, thanks to the science behind it, we connect with it on a level that goes beyond surface knowledge alone.
References
1. The discovery of parafin is generally attributed to French chemist Michel Eugene Chevreul (1786-1889).
2. For more information on capillary action, see US Geological Survey, "Capillary Action", article online at http://ga.water.usgs.gov/edu/capillaryaction.html
3. The National Candle Association, "Colorants", article online http://www.candles.org/elements_colorants.html Accessed June 9, 2010.