A candle has a set number of hours in it, and a surprising share of them get wasted on the first evening, or by a wick that never gets trimmed. Ours have up to fifty hours in the After Dark jars and about fifty to sixty in the Open Hours jars, and you can have nearly all of them if you do four small things. None of them takes a minute.
The first burn goes to the edge
The first time you light it, keep it going until the melted wax reaches the glass all the way round. In a jar this size that takes two or three hours, so light it on an evening when you have the time. Wax remembers the first ring it makes, and every burn after that will stop where the first one stopped. Put it out early on the first night and you get a tunnel down the middle with a wall of wax around it that never melts. Give it the full first burn and the whole top will go down evenly to the bottom of the jar.
Keep the wick short
Before you light it, every time, trim the wick to about a quarter of an inch. Ordinary scissors will do while the wax is cold, and nail clippers work well once the wick is low in the jar. Take the trimmings out of the wax so they do not end up in the flame. A long wick gives you a tall, restless flame, black marks on the glass, and a jar that empties itself in a fortnight. A short wick burns low and slow, and that is where the extra hours come from.
Four hours, then a rest
Do not burn it for more than about four hours at a stretch. After that the end of the wick starts to ball up and smoke, and the glass gets hotter than it needs to. Put it out, let it cool right down, trim the wick, and it is ready to go again. If the flame ever gets tall and jumpy, or the glass starts to blacken, the candle is asking to be put out and trimmed, so do that rather than waiting for the four hours to be up.
When to stop
Stop burning it when about half an inch of wax is left in the bottom. Below that the flame sits too close to the glass and the heat has nowhere to go. It feels like a waste, but the last half inch was never going to burn well anyway, and a jar that has cracked from the heat is a worse end than a little wax left over.
Keeping it safe
Burn it on a flat surface that can take some heat, away from moving air, and away from anything that can catch, which includes the book and the blanket. Keep it where you can see it, out of reach of children and pets, and leave it where it is while it is lit or the glass is still hot. A snuffer is the kindest way to put it out. If you blow it out instead, do it gently and let the wick stop smoking before the lid goes back on. Never leave it burning in a room you have walked out of, and if you read in bed, put it out before you get drowsy rather than after.
