Cooling
Updated
The twenty minutes after pouring decide the surface, and almost nobody controls them.
Slow and even
Natural wax wants to cool slowly and steadily. Fast cooling gives a crust over a still-liquid middle, which is a sinkhole.
Uneven cooling gives one side frosting or wet spots and the other not, which is maddening to diagnose because the formula was identical.
Stable room temperature, no draft, no direct sunlight, not on a cold stone bench.
Where to put them
A single layer on a board, spaced so air moves evenly around each one.
Not in a tight block, where the middle candles cool slower than the edges and come out different.
Not near a door or a window that will be opened. A draft across half a tray is a common cause of a batch that is half good.
Do not move them
A candle that looks set on top can be liquid underneath. Carried, it develops a wave in the surface that sets permanently.
Leave them alone until they are cool through, which is hours rather than minutes for a larger vessel.
The second pour
If the wax sinks around the wick, top up with wax from the same batch held at pour temperature.
Wait until the sink has formed and the surface has set, then top up. Too early and it merges and sinks again; too late and there is a visible ring.
Keep the reserve covered so it does not lose fragrance relative to the body of the candle.