How to Burn Test a Candle Properly

A burn test means burning a finished candle in controlled sessions and writing down what it does, from the first light to the last of the wax. Maker guides based on ASTM F2417, the fire safety standard for candles, use the same pattern: burn for 4 hours, let it cool, repeat. Never leave a burning candle out of sight. Test in your own jar with your own wick and wax, because a result from someone else's candle does not carry over.

How do I run a burn test, step by step?

1. Cure first, then wait. Let the candle cure (see our cure guide), and wait at least 24 hours after pouring before any wick test, as CandleScience advises. Label each candle with its recipe and wick.
2. Set up a safe spot. Use a flat, heat-resistant surface away from anything that can burn, drafts and kids or pets. Armatage suggests a room between 68 and 86 degrees F (20 to 30 C). Craftybase says to keep multiple candles 3 to 6 inches (8 to 15 cm) apart. Armatage rounds up to 8 inches (20 cm) around each candle. Wider is safer, because close candles heat each other.
3. Trim the wick to 1/4 inch (6 mm). Do this before every session, not just the first.
4. Light it and note the start time. Stay in the room. Armatage says to check the candle at the start and every hour after that for flame height, jar condition, heavy black smoke, damage to the surface, and tipping or spilling.
5. Check at 2 hours and 4 hours. Look at the melt pool and the wick at 2 hours, then again at 4. Measure the flame height at least every 4 hours. Then put the flame out.
6. Let it cool completely. Craftybase says at least 5 hours.
7. Repeat until it is done. Keep going until the candle fails a check or the wax is used up. Armatage says that can take a few weeks overall.

What counts as a fail?

Stop the test and mark the candle as failed if any of these happen:

• The flame gets too tall. Armatage quotes the ASTM F2417 limit as under 3 inches (7.6 cm), or 3 3/4 inches for candles meant for religious use. ASTM now lists F2417-26 as the active edition, so confirm against the current standard.
• The jar cracks or breaks.
• Heavy black smoke.
• Damage to the surface it sits on.
• The candle tips or spills.

Armatage also treats two things as its own extra checks, not ASTM ones: an outer container hotter than 140 degrees F (60 C), and carbon balls bigger than 3/16 inch (5 mm). Our jar heat guide explains why that 140 figure should be handled with care.

Worked example: how long a test takes

Say your candle should last about 40 hours. All numbers are examples.

• Sessions: 40 hours / 4 hours = 10 sessions
• Cooling: each session needs at least 5 hours before the next one
• Pace: two sessions in a day (say 8 am to noon, then 5 pm to 9 pm) gives 5 test days

If you compare three wick sizes at once, run them the same days, side by side. You do not need to test all 40 hours of every candidate. You can drop clear losers after the first session or two and run the finalists to the end.

Is there a shorter test?

Craftybase describes a basic 4-hour test: burn once, then check if the candle burned evenly across the full width with less than 1 cm (about 3/8 inch) of wax left on the sides. It says a full test can take a few days to several weeks. A basic test is fine for a quick wick comparison. It will not catch problems that only show up later in a long burn.

Common mistakes

• Testing an uncured candle and blaming the wick for a weak scent.
• Leaving the room. Burn within sight is one of the three standard warning statements.
• Skipping the wick trim between sessions.
• Letting the candle get only part way cool before relighting.
• Not writing it down. A test you cannot compare is just a candle you burned.
• Judging a wick on one test only. Retest when the wax batch, the oil or the dye changes.

Questions

How long should a burn test session be?

Four hours is the usual session for most candles, with 2-hour checks along the way. Armatage lists 8-hour sessions for gel candles and a single burn to the end for tealights. Our guide on test length goes deeper.

Do I need to follow ASTM F2417 to sell candles?

CPSC lists ASTM F2417 as a voluntary standard for candle fire safety, along with others for labeling and glass containers. Voluntary means CPSC has not made it a mandatory rule, but your insurer or a shop may ask for it. I am not a lawyer. Ask them, and check the current standard on the ASTM site.

What should I write down?

At minimum: date, recipe, wick, flame height, melt pool width and depth, wick condition, jar heat and any soot. Our burn test log guide has a full list.