Why do I occasionally see soot coming from my soy candle?

Check the wick length.  If the wick is longer than 1/4", it’s time to trim.  Do not attempt to trim the wick while the candle is lit.  Extinguish the flame, trim the wick and relight.  It is best to trim the wick to 1/4" every time you light your candle.  It is also important to burn your candle away from drafts.  Drafts can cause the flame to burn hotter and erratically, thus causing soot to appear. The soot from a soy candle is a lighter, white soot that cannot always be seen. The black soot on the glass rim in all-natural candles comes from a wick issue, not petroleum pollutants like in paraffin wax.   To keep the soot to a minimum, remember to only burn candles one (1) hour for every inch of it's diameter, keep the wick trimmed to 1/4" and keep the candle out of drafts. Also, it is very important that wick trimmings are NOT left in the candle wax (or matches, etc.).