Visible soot or black smoke
Sooting indicates incomplete combustion. It stains walls, soils lungs, and signals an over-wicked or over-fragranced candle. Treat as a safety priority, not a cosmetic issue.
Why this happens
Soot is unburned carbon. It appears when the fuel-to-oxygen ratio at the flame is wrong: usually too much fuel from an oversized wick or an untrimmed one, or draft-disrupted airflow. It stains ceilings, deposits on lungs, and is the single strongest indicator of an unsafe candle.
Likely causes
- Wick over-sized.
- Untrimmed wick (over 6 mm).
- Fragrance load too high or contains heavy aromatics.
- Draft causing flame instability.
How to diagnose
- Trim wick to 5 mm, retest in a draft-free space.
- Burn a control candle (same wax, same wick, zero FO) and compare.
Change sheet · next batch
Fill in what you know. The change sheet below re-orders so the delta most likely to help your specific batch floats to the top.
Cut fuel delivery until the flame runs clean.
Trim before every burn, cap sessions at 4 h.
Heavy aromatics contribute soot on top of the wick.
Even mild airflow flickers the flame and breaks combustion.
Take action
- Wick mushrooms and carbons up
Carbon ball on the wick tip, sometimes glowing red.
- Flame jumps, flickers, or pops
Unstable flame, often paired with crackling.
- Candle fire safety: BS EN 15493 and a real burn-test protocol
BS EN 15493 sets the fire-safety bar. Here is the standard, plain English, plus a 4-burn test protocol.