In addition, you should select glassware that is stable and not easy to tip. The use of very narrow glassware should also be avoided. Besides potential blackening of the glass from candle combustion, a factor that is known as gel pool comes into play. This is the area around the candle flame of melted gel. Too much or too little of a pool will cause incomplete combustion which creates a lot of smoke.
Bubbles fall into two categories, wanted and unwanted.
Often times bubbles are wanted in candles such as champagne glasses or other bubbly beverage designs. More often you want to get rid of them. Hotter pours are generally the answer. Preheating or warming the glassware you pour into helps. Keep an eye on the items you embed or add to the gel.