How Long Should a Candle Burn Test Be?

A burn test session is usually 4 hours, with a check every hour before you put the flame out. Then the candle cools, and you repeat until it is used up. Armatage says standard candles are burned in four-hour increments, and that the whole test can take a few weeks depending on size. A shorter 4-hour test is fine for a first look at a wick. Do not leave a burning candle out of sight, and test in your own jar with your own wick and wax.

What are the session lengths?

• Standard candles. Armatage burns in four-hour increments until the candle fails or the wax is used up.
• Gel candles. Armatage lists 8-hour periods.
• Tealights. A single burn until the candle goes out.
• A new fragrance. Craftybase suggests extending to 8 hours for a customized test.
• Quick wick check. Craftybase describes a basic 4-hour test: burn once, then see whether the candle has burned evenly across the full width with less than 1 cm (about 3/8 inch) of wax remaining.

I could not open the paid ASTM F2417 text, so I cannot say where the 4-hour session comes from. Armatage presents its steps as the ASTM burn test, and Craftybase refers to "the ASTM candle burn test", but neither quotes the standard's text, and ASTM's public page gives no session length. CPSC lists ASTM F2417 as a voluntary standard for candle fire safety.

How many sessions is that?

The guides give no fixed number. Sessions = total burn hours divided by session length, and the total comes from how fast your candle burns. The check points inside a session are: look at the start and every hour (Armatage), record flame height at least every 4 hours, and trim the wick to 1/4 inch (6 mm) before each session. Craftybase says to cool at least 5 hours before the next one, so two sessions in a working day is a practical most.

Worked example: planning the test

Weigh a candle before and after one session to get its burn rate. This is my own habit. Say it loses 1.0 oz (28 g) in 4 hours, which is 0.25 oz an hour. These sizes and rates are examples.

Check the large one: 50 hours / 4 = 12.5 sessions, and 13 sessions at 2 a day is 6.5, so 7 days. Add days if you only burn on weekends. Real burn time also depends on the wax and the wick.

Do I have to burn the whole thing?

Not for every candidate. Craftybase calls a full test days to several weeks. My own practice is to run three wick sizes through a first session or two, drop the clear losers (tunneling, a flame that goes out, a flame that is too tall, soot), and run the finalists to the end. CandleScience's wicking guide says to test all candles at the same time so they are easy to compare, and to let a candle burn 3 to 4 hours at one lighting before judging the melt pool. Some problems, such as a tunnel forming or a jar that keeps heating, show up late, so the finalist needs the full burn.

What should I check each session?

Every hour, and at the end of the session: flame height, melt pool width and depth, wick condition and carbon, jar heat, soot, and any damage to the surface under it. Fail the candle if the container cracks, the flame is too tall, heavy black smoke streams from the wick, the candle damages the surface under it or tips. Our log guide has the full list.

Common mistakes

• Leaving the room mid-session.
• Relighting a half-cool candle.
• Skipping the trim between sessions.
• Stopping at 4 hours and calling the wick proven.
• Testing at different times, so the candles are not side by side.
• Not writing times down.

Questions

Can I run the whole burn in one go?

Not under the method these guides describe. They break it into sessions with cooling in between. A candle burning 40 or 50 hours straight is hard to supervise, and I found no guide that recommends it.

Is 4 hours enough to pick a wick?

It is enough to cut weak candidates, not to prove the last one. Craftybase calls its 4-hour test a basic test. Run the finalists to the end, and retest when the wax batch, the oil or the dye changes.

How long should I wait to start?

CandleScience's wicking guide says to wait at least 24 hours before starting a burn test, and your wax may need a longer cure.