How to Conduct a Basic Burn Test
Burn Test Fundamentals
In candle making, a burn test establishes that a candle meets safety and performance standards.
Each candle in a test is burned in four hour increments until a failure condition occurs or the entire candle is used up.
These tests can take as long as a few weeks to complete depending on the size of the candle because each event needs a completely cooled candle to start.
Candle makers leverage candle tests to prove their candles are safe and have an appropriate hot throw in use.
Gas chromatography-olfactory can measure the actual strength of scent (through analysis of odorous volatile organic compounds), though this is not common.
Since scent is mainly subjective, burn tests focus more on safety metrics, not hot throw.
Learn more about testing for hot throw here.
Candles are a beautiful combustion machine. The wax blended with fragrance oil acts as fuel carried by a wick to a flame.
This delicate balance of fire and fuel is combustion. Well-made candles harness combustion to fill rooms with aroma without sacrificing safety.
Poorly-made candles burn far too hot, don’t completely combust, or plain don’t have any significant hot throw about them.
Even if you aren’t selling candles, burn testing helps inform how well designed your candle is so you can optimize performance while observing safety standards.
After all, candles are a form of controlled fire. It’s so important to be careful with your design for this reason, especially if you don’t have any candle insurance.
The companionship of your fragrance oil, wax and wick are the primary metric of a candle burn test.
Thicker fragrances and high-viscosity waxes (beeswax and soy) require a more significant wicking system to throw properly without becoming too hot whereas thinner fragrance oils and low-viscosity waxes (coconut and some paraffin) don’t need a robust wick to perform safely.
A burn test reveals if you need a larger, smaller, or completely different wick.
Before-Testing Checklist
Create & cure candles
You can’t burn test without having candles ready!
You should substantially cure any candles primed for testing. What does this mean? Wait the recommended amount of time for your primary wax blend before setting up a burn test.
A lot of candle makers lack patience to wait for their candles to cure or they don’t believe in polymorphism, but wax changes dramatically while it hardens.
Natural waxes, like soy or palm, structurally harden over the course of their life as crystals continuously form. They are sensitive to temperature fluctuations, which is also the leading cause of frosting.
With natural waxes, the first two weeks are critical to its performance and stability.
They harden over time, so test results from early in their life tend to be misleading (on the side of being too small).
Most paraffin is relatively inert and extremely stable, which means they don’t change much after their initial hardening. Burn testing paraffin after 24 hours will yield similar results to a two week burn test.
Use this guide as a starting point for curing:
- Vegetable wax: 14 days
- Paraffin wax: 24 – 48 hours
- Blends: 1 days – 14 days
Pick a test type
Most tests capture information about safety or performance. Each has nuances worth considering.
There are a variety of safety tests you can conduct:
- Standard burn test (described in this article)
- Chaos test/power burn
- Common behavior testing
Performance testing, also known as does-this-candle-smell-as-strong-or-as-good-as-I-want-it-to testing, is hard to do with multiple candles consistently, unless you have multiple areas in your workshop (or home) with expected hot throw results.
It is easier to test this in isolation (read: in someone’s home) after a candle passes a safety test.
Prepare test area
If you intend on burning multiple candles, prepare a location where each candle has 7 7/8″ (just round up to 8″ if you don’t want to be unreasonable) of space around it.
The room should be 68 to 86 °F (20 to 30 °C) to provide a consistent atmosphere for burning in as well.
Place the candles in a tray big enough to hold the entire melt pool if the container cracks or the candle tips.
Also, clearly mark each test candle with information about it’s wick and any distinguishing information about the wax blend that might be helpful.
Create a consistent environment if you intend to test the hot throw – for instance, many candle makers test the hot throw of a single candle in a medium sized room with no drafts while gathering the opinion of every “smell critic” in the area (more opinions are better than one given the nature of scents).
Basic Burn Test Procedure
Industry standards
While not the law, industry standards serve as voluntary standards for candle makers as it pertains to testing. ASTM F 2417 is the primary source for standard candle testing.
It outlines procedures, provides clear definitions for all components of the standard, and characterizes all fail points of a burn test.
By no means do you have to comply with everything in ASTM, but following the procedures and meeting the criteria for safety testing can be the difference between winning or losing in a court of law, even with a voluntary standard.
Enough about that – you should know better than to sell candles that aren’t safe!
Burn test algorithm
Testing candles is relatively straight forward. Standard burn testing requires consecutively burning the candle for a certain time period until it fails or runs out of wax.
- Tealight – a single burn event until the candle extinguishes
- Gel-containing candles – 8 hour periods
- All other candles – 4 hour periods
The ASTM standard burn test, called the Candle Burning Performance Test, outlines the following procedure:
- Prepare the test area as described above, making sure to clearly mark each candle for reference throughout the test.
- Trim the wick to 1/4″ length every time.
- Initially after the burn, and on every hour, record and/or visually observe:
- Maximum flame height (bottom of flame arc to top of flame tip) is less than 3″ (or 3 3/4″ if the candle is intended for religious use)
- Container is intact, not cracked or broken
- Black smoke isn’t excessively streaming from the wick
- Container hasn’t damaged the surface it’s sitting on
- Candle hasn’t tipped over or spilled
- Record the flame height at least every 4 hours, even if you’re “looking at it” every hour.
- Consider the candle failed if any criteria in #3 aren’t met.
- After the candle cools, repeat steps 2 through 6 until the candle fails or runs out of wax
Interestingly, ASTM F 2417-17 doesn’t mention anything for temperature control or carbon formation, but they are also good reasons to fail a candle (even if they aren’t industry standard markers):
- Carbon balls must remain smaller than 3/16″ (5 mm)
- Outer container temperature remains at or below 140 °F (60 °C)
Test results
Your wick is too big or too hot if…
- Container temperature exceeds 140 °F
- Carbon balls form that are greater than 3/16″ (5 mm)
- Excessive soot or black smoke forms from wick
- Flame height is greater than 3″ (or 3 3/4″ if the candle is intended for religious use)
- The melt pool is too large
Your wick is too small, or requires multiple wicks, if…
- Candle begins tunneling or leaves a significant amount of wax on the sides
- Flame self-extinguishes before the candle finishes
- Candle finishes with a significant amount of wax on the edges, even after subsequent burns
Other Tests
The testing described above is the industry “by the book” method for validating candle safety, but there are many different types of testing chandlers undertake during candle development.
Performance Test
How strong does the candle smell? This is arguably as important as safety testing for some people.
What good is a perfectly safe candle if no one can smell it? Procedures for this vary wildly – some at-home candle makers set up elaborate hallway measurements to literally measure the length of the hot throw.
Others ask friends, family, or coworkers to rate the scent on an arbitrary scale.
Smell is highly subjective – some people are overwhelmed by smells that wouldn’t bother an entirely different group. Some love a faint scent that triggers a happy memory, even if it isn’t a “strong” smell – scent is strongly connected to emotion.
A framework for exploring performance is the BLO Test. Read more about that in our guide for measuring hot throw.
Chaos Test
More elaborate testing by candle makers also includes chaos testing, or “power burn” tests.
Although safety stickers suggest a maximum burn time of four hours, many customers do not listen to this (not because they are evil, but because your candles are amazing, obviously!).
Variance Test
Besides power burns, candle makers may include variance testing too.
These burn tests capture the variability in how well customers treat their candles for trimming or wild conditions. Instead of a steady, terminal period of burning in a controlled area, test burn the candle without trimming the wick and possibly in larger areas subject to more air currents.
The idea behind variance testing is to see what more realistic conditions might look like (besides power burning) and accommodate it for performance and safety where possible.
If all else fails… you can always pay someone to test your candles for you!
Free Printable
If you’re interested in a downloadable PDF template for conducting burn tests, join our free newsletter (The Armatage Candle Company Academy) with the below sign-up and we’ll send it to you.
The PDF includes:
- Organized data entry positions for a single candle – print off one for every unique candle being tested
- Easy-to-follow locations for entering data
- No watermarks or weird Armatage Candle Company branding… this is yours to use however you wish
- Fill-in-the-blanks for every failure and passing criteria
Sign up, and we’ll also give you access to our entire freebie library, including the 18-page eBook, Candle Math for Newbies.
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