How to Stop Candles From Sooting and Mushrooming
A candle that sends up black smoke, leaves dark soot on the rim of the jar or forms a black carbon ball on the end of the wick is not burning cleanly. This is one of the most common issues in homemade candles and store-bought ones alike. It is usually a sign that the flame is receiving more fuel than it can burn efficiently, whether because the wick is oversized, untrimmed or struggling with the fragrance and dye in the wax. Most sooting can be solved with testing and a few simple habits.
Why candles soot
A candle flame burns melted wax drawn up the wick. When the flame is too large or disturbed, it cannot burn all the fuel completely, and unburned carbon particles escape as visible smoke and soot. A flickering, dancing flame is especially prone to sooting.
Wick mushrooming happens when carbon builds up at the tip of the wick faster than it burns away, forming a black ball. Mushrooming often goes hand in hand with an oversized flame and can drop hot debris into the wax pool.
Check wick size
An oversized wick is the most common cause of sooting in homemade candles. It melts wax quickly, creates a tall flame and draws more fuel than the flame can burn cleanly, which also makes jars overheat.
Burn test several wick sizes in the same vessel, wax and fragrance combination. Choose the wick that produces a steady flame and a full melt pool within a reasonable time without excessive height or smoke.
Trim the wick before each burn
Trim wicks to about 1/4 inch (6 mm) before lighting, or follow the wick manufacturer's guidance. A long wick produces a larger flame and more soot.
Remove any carbon mushroom before relighting. Wick trimmers make trimming easier in jars, and trimming keeps flames steady and clean.
Review fragrance load and additives
High fragrance loads and heavy dye use can cause wicks to clog and mushroom. Some fragrance oils are also more prone to sooting than others.
Stay within the wax manufacturer's recommended fragrance load and use dyes sparingly. Test each new fragrance, since changes may require a different wick size.
Avoid drafts
Air currents from fans, open windows, vents and people walking by make flames flicker and smoke. Burn candles in still air on stable surfaces.
Advise customers and gift recipients to avoid burning candles in drafty areas. Proper burning conditions improve safety and performance.
Burn for appropriate times
Burning candles for too long can cause wick build-up and overheating. Many candle makers recommend limiting burn sessions to about four hours.
Let candles cool, trim the wick and relight. Include burn instructions on labels to help customers get clean burns.