Soot, carbon and mushrooming

Combustion quality is read off the wick and the glass, and both are visible during the test rather than after it.

What the wick tip tells you

A clean burn leaves a small, slightly curled tip that self-trims.

A carbon ball means the wick is delivering more fuel than the flame is burning cleanly. Incomplete combustion, and the excess is going somewhere: the glass, the air, the ceiling above a customer's shelf.

Soot on the glass

A dark ring on the inside of the vessel above the melt pool.

A trace on a long burn is ordinary. A visible band after one four-hour cycle is not, and it is the complaint customers report as the candle being "dirty" or "smoky".

Check the ceiling above the test candle too. That is where a customer will see it in their own home, and it is the one they will be angriest about.

Carbon ball at the tip

Usually too much wick for the wax, or a fragrance load the wick cannot burn cleanly.

It is also self-worsening: the ball increases fuel draw, which increases the flame, which builds a bigger ball.

A candle that needs trimming every hour to behave is a candle that is wrongly wicked, not a customer who is not following the instructions.

What to do about it

Drop a wick size and retest. That is the first move and usually the answer.

If dropping a size then causes tunneling, the fragrance load or the wick type is wrong rather than the size, and the fix is a different wick series or less fragrance.

Do not solve it by putting "trim your wick" on the label and considering it addressed. That instruction belongs there anyway, and it is not a substitute for a candle that burns clean at four hours.

References