Reading the melt pool

The melt pool is a informative thing a burning candle shows you, and it is read in two directions.

The two numbers

Diameter: how far across the surface has liquefied.

Depth: how far down.

A wick that is too small fails on diameter. A wick that is too large fails on depth. Both are visible within the first few hours.

Full melt pool

The wick should reach the vessel wall within about four hours on the first burn.

Under-wicked and it does not, which sets the tunnel that the candle will follow for the rest of its life. Wax has memory: the first burn writes the pattern.

Over-wicked and it reaches the wall in an hour, which is not a good result either. It means the candle is running hotter than it needs to, which shows up later as a hot vessel and a short burn time.

Depth, and the other failure

A melt pool much deeper than about 12 mm is a warning. Deep pools mean a lot of liquid wax, a hot vessel and a wick drowning in fuel.

Deep and narrow is the worst combination: too much heat going down instead of out. It usually means the wick is wrong for the wax rather than wrong for the diameter.

What a good result looks like

Full melt pool at the wall within three to four hours, depth staying moderate, a wall of wax that melts evenly on the way down, and a vessel you can still hold.

Take a photograph at the end of each cycle. Melt pool behavior is far easier to compare across candles from a photograph than from a note, and it is the comparison that tells you whether a wick change helped.

References