This section provides “how-to” advice for students undertaking science projects involving candles. It also includes brief descriptions of possible project ideas.
Although we recognize that science projects involving the burning of candles are often undertaken by elementary school students, the National Candle Association strongly discourages the use of candles by children, and does not recommend candle science projects for children under the age of 12, even with adult supervision.
Follow the Scientific Method
With any scientific experiment, you want to eliminate every variable except the one you’re investigating. This helps ensure that your observations are correct reflections of what actually happened and why.
Unfortunately, candles involve a lot of variables. Every element of a candle — size, shape, wick, wax, fragrance, dye, etc. — impacts its burning behavior.
Two candles that appear to be the same may actually be very different. If made by different manufacturers, they probably contain different waxes, different wicks, different dyes, different fragrances, etc.
Eliminate Variables. A good way to help eliminate unwanted variables in your experiment is to use the same size and style candle made by one manufacturer, making sure that the only difference is the variable you’re testing.
Unless you are testing for the influence of fragrance or dyes, use uncolored and unscented candles. If you are testing the effect of different waxes, make sure you know exactly what type of wax the candle is made from.
Manufacturers frequently use a blend of different waxes. It may not be possible to determine exactly what type of wax is used in a particular candle.
A Stable Flame. Before starting, trim the wick to 1/4 inch (tapers or dinner candles should be trimmed to 1/2 inch.) After lighting the candles, wait several minutes until the combustion process has stabilized. The flame should be burning steadily without any notable flickering, and an even pool of melted wax should surround the base of the wick.
Be sure to place test candles out of drafts or air currents, which can interfere with the combustion process and make the candle burn irregularly.
If burning candles simultaneously, make sure there is plenty of space between them (at least 8 inches) so the flames don’t “draft” one another.
Multiple Samples. If possible, test three samples of each candle type, or run your experiment three times. Even same-batch candles will have slight variations. Testing multiple samples provides more data and more accurate results.
Record Your Observations. Use a notebook to record all of your measurements for each candle tested. Be sure to take pictures to illustrate your findings. A digital camera works best, since you can immediately view and save the photo, or reshoot if necessary.
Possible Topics for a Science Project
Does the color of a candle affect its burn rate?
This is probably the most popular candle science project with younger students. Dinner candles (tapers) are probably the easiest to use for this experiment, and are readily available at grocery and drug stores.
Be sure to purchase the same size, unscented candles made by one manufacturer, and varying only by color.
Mark each taper with a horizontal line 1/2 inch below the lip of the candle, and again at a point 2 inches below that. Once the candle has burned to the first mark, begin recording the time it takes until the candle burns to the second mark. Compare the times for each different colored candle.
More advanced students can measure the weight of the candle before and after burning the candles for a set amount of time to obtain more precise data (e.g., grams of wax consumed per minute or hour).
Does temperature affect a candle’s burn rate?
Use the same experiment set-up as above. You can compare candles that have been placed in the refrigerator to candles at room temperature, or you can compare candles burned in a heated room versus an air-conditioned room. Be sure the temperature difference is at least 20 degrees.
Caution: If you put the candles in the refrigerator, be sure they are tightly wrapped so that moisture does not get into the wick. A damp wick will alter its burn characteristics, adding an unintended variable.
Do not freeze candles. Handling candles this cold may cause them to crack and lose their integrity, making them unsafe to burn.
Does wick size affect the burn rate of a candle?
Does wick size affect flame height?
You will probably need to order candles from a candle supply house to make sure they are the same size and wax type, but have wicks of different diameters. The wicks should be the same style and made from the same material, preferably from the same wick manufacturer.
You can use either the mark-to-mark or before-and-after weight method to measure the burn rate discussed in the first entry-level project idea. To measure flame height, place a metal ruler in a clamp stand next to the candle, aligning the ruler so that you can easily see and record the flame height, as well as capture the measurement in a photo.
Does wax type affect a candle’s burn rate?
Does wax type affect flame height?
Does wax type affect the brightness of the flame?
These experiments are best done by ordering candles from a supply house, making sure they are the same size and shape, differing only by wax type.
You should be able to purchase pure paraffin, beeswax or soy wax from most candle supply stores. Use the before-and-after weight method to determine the burn rate, and the metal ruler-clamp stand method for determining flame height. A light meter can be used to determine brightness.
Does fragrance impact a candle’s burn rate?
Does fragrance impact flame height?
This project can be done by selected several different fragrances from one manufacturer’s line of “spa-style” jar candles.
Spa candles typically feature white or cream-colored wax in clear or frosted glass jars. Because the waxes and wax color (if any) are the same, the only variable is the fragrance. Select 3 or more fragrances. Use the before-and-after weight method to determine the burn rates. Use the metal ruler-clamp stand method to measure flame height.
What is the temperature of a candle flame?
Is the temperature of a flame uniform?
Do wax pool and flame temperatures correlate?
This experiment requires a J-type thermocouple (a sophisticated type of thermometer for measuring high temperatures) and is only suitable for students with access to advanced lab equipment. Follow all previously discussed procedures to ensure proper sampling, measuring and the control of variables.