Mushrooming occurs when there is too much molten wax fuel for the wick to combust, thus creating a build-up of partially reduced molecules which can't reach the flame and burn off. The unburnt material falls back on to the wick and causes a build-up of carbon on the end of the wick (carbon cap). This can be caused by an oversized wick providing more wax to the flame then it can burn. Or using the wrong wick for the type of wax being burnt.
The burn pool of a candle is the pool of molten (melted) wax surrounding the wick, it is this wax that is drawn up through the wick and combusted via the flame. The picture to the left shows a melt pool that is too small for the candle causing the wax to tunnel. This is where the wax doesn't melt evenly and therefore reduces the overall melt time of the candle. This is a sign of a less efficient burning candle which can be caused by the wick being too small or the wax is too hard.
As you can see by this picture the melt pool covers the entire candle and therefore you are getting the maximum burn time and efficiency out of your candle. There is no wasted wax at the sides and this will burn down evenly. If you find that you have a mushrooming wick as well as a melt pool this size, you may want to down size your wick.
If the flame is small and struggling to stay alight this means the wick is drowning and therefore you will want to wick up.
A drowning wick occurs when either the wick is too small, or it is getting clogged up because there is too high a concentration of dye or fragrance in the wax causing the wick to struggle. Try a larger wick or less fragrance next time round.
This occurs when there is air trapped in either the wick or the wax. Be careful when melting the wax to ensure that no water from the double boiler finds its way into the wax. Likewise, when waxing your raw wicks that there is no air left in the wick. Another fix for this could be to wick up.
Flame too Big or Small
If your flame is too large this can be because the wick is too big, so use a smaller wick also ensure that the wick has been trimmed down to about a centimetre above the candle.
If the flame is too small you need to use a larger wick. A flame that is ½ - ¾ of an inch high is the perfect size.
Cracks in the Candle
If a candle is cooled too quickly this can cause cracks/frost lines on the exterior of the candle. Some people will do this intentionally for an effective outcome like in the picture.
However, when this happens without planning it can be very annoying, a way to solve this is to reheat the sides of the candle either by dipping it into a hot water bath or using a hair dryer.
If you want to achieve this look I would recommend cooling the candle in a fridge or freezer.
Re-pour Not Blending
When the re-pour doesn’t blend with the original pour this can be because you have poured the wax at a different temperature to the first one.
You need to re-pour the wax at the same temperature and whilst the candle is still warm and not fully hardened yet.
If they don't still blend you can fix this by heating the wax with a hair dryer.
Smoking Candle Flame
There are a few things that can cause your flame to smoke these being a wick that is too large causing the wax to be too hot, or there is too much fragrance and dye mixed in the wax causing the combustion of the gases and chemicals to struggle.
If your candle is lit in a drafty area the smoking can be caused by non-combusted soot (carbon particles) this happens because the draft is cooling the gases before they are oxidised in to the atmosphere there for the gases are realised as a soot.
This is also why a wick smokes when blown out it is the release of all the non-combusted soot that has been rapidly cooled.
As a candle cools it naturally shrinks, this is normal and unavoidable. There are ways that you can help reduce the amount your wax shrinks. For example, try warming the mould or container prior to pouring your wax into it. Pour your wax at a lower temperature meaning some of the shrinking has already occurred.
You will need to do a re-pour to fill in your sink hole as the candle starts solidifying sometimes you will need more than one re-pour.
Wet Spots or Air Bubbles
This is caused when the wax closest to the container is cooled to quickly and therefore shrinks and pulls away from the jar.
You can minimize the effects of this happening by warming the glass and cooling the candles at a warmer temperature. Pouring the wax at a hotter temperature may help along with pouring slowly and carefully. Tapping the mould and the container may also help to release the bubbles.