Most candles die long before the wax runs out. Almost always it’s one of four things, and all four are easy to fix.
1. Respect the first burn
Wax remembers the shape of its first melt pool. Light a new candle and leave it until the pool reaches the glass — usually two to three hours on a 180 g jar. Blow it out early and the candle will burn a narrow shaft down the middle for the rest of its life, stranding a ring of wax you paid for.
2. Trim the wick before every single burn
Five millimetres. A long wick makes a tall, flickering flame that eats wax fast, throws soot onto the glass, and mushrooms into a carbon ball. Trimming takes four seconds and is the single highest-return habit in this list.
3. Stop at four hours
Past about four hours the wax overheats, the flame grows, and the fragrance starts burning off instead of evaporating. Put it out, let it set for an hour or two, and light it again later.
4. Mind the draught
An open window or a fan pulls the flame sideways, which burns the wax unevenly and doubles the soot. Move the candle rather than fighting the flame.
Do all four and a 45-hour candle really does give you 45 hours — with a clean jar at the end of it.