Do your candles have sinkholes in them? Is your wick giving off lots of black smoke? Perhaps your wax is pulling away from the glass, leaving a noticable gap between your candle and vessel? Here we will go through some of the common problems chandlers encounter, why these occur and how you can avoid them in future. Continue reading to find out more!

Tunnelling

What Causes tunnelling?

Sinkholes, also known as cavities, are gaps or voids that are formed inside or at the surface of a candle as the wax contracts during the cooling and curing process. Sinkholes are more common in mineral wax than in plant wax, as mineral wax shrinks more during cooling, but sink holes can also occur in plant wax. 

Why is my candle tunnelling?

“Tunneling” occurs when a candle is under-wicked. The wick produces a flame that isn’t strong enough to melt the wax all the way across the top of the candle, so the diameter of the melt pool is too small and remains so for the duration of the candle’s life.  This should not be confused with normal hang-up, which is common in the early burns of a candle.  Hang-up is wax residue (usually not more than 0mm thick) on one or both sides of the candle.  Hang-up will typically melt as the candle burns down. So…Tunnelling is technically ‘excessive’ hang-up that does not improve as the candle burns down.

How do I avoid sinkholes?

Double Pour

The risk of sinkholes can be reduced by using the “double-pour” candle pouring technique. Here, a container candle is poured in two stages. Typically, the first pour will fill 70-90% of the candle. After cooling, when the wax has contracted, the second pour fills the candle to the desired level. As mineral wax shrinks more than plant wax, the double-pour technique is particularly useful for mineral wax blends.

Pouring temperatures

Sinkholes can be avoided by pouring candles at ecommended pouring temperatures. For example, Candle Shack’s EcoSystem RCX rapeseed & coconut wax should be poured at 38-40°C, and Candle Shack’s CS1 mineral wax should be poured at
>65°C.

How do I fix candles with sink holes?

Relief hole

A “relief hole” can be created by puncturing the wax above a sink hole after the first pour of the candle. The void can then be topped up with melted wax. This
technique works well with mineral wax and can be used to complement the “double pour” technique, especially with larger candles.

Heat gun

For sink holes near the surface of the candle, a heat gun can be used to melt the surface of the wax above the sink hole. The melt pool formed by the heat gun will flow into the sinkhole and leave a level surface.

Mushrooming

Why is my wick mushrooming?

Clubbing, or “mushrooming” as it is referred to in extreme cases, is caused by incomplete combustion of the wax and fragrance oil. This can occur when too much fuel is being delivered to the wick compared to the amount of oxygen being supplied, leading to the formation of carbon deposits on the wick.  It should be noted that for highly scented candles, clubbing cannot usually be completely avoided.

Which wick should I use with my wax?

The choice of wick will depend on which wax is being used. LX or TG wicks work well with mineral waxes. Stabilo, CL, V, TB, ECO or PGS wicks can be used with
mineral or vegetable blends, while VRL wicks are suited to blends containing a high percentage of plant wax.

How do I prevent candles from mushrooming?

Mushrooming is often a sign that a candle is overwicked, so down-wicking can reduce the effect, although this will create a smaller melt pool. Sometimes it will be necessary to change to a different wick family to reduce clubbing or mushrooming. Occasionally, a fragrance oil will cause clubbing regardless of
the wick used. In such cases, a different wax blend may improve the situation. Minor clubbing is very common, and is not normally a cause of concern.

Glass adhesion

Why does the wax pull away from my jar?

Candle wax shrinks as it cools from liquid to solid. After the initial pouring, the liquid wax will be in contact with the glass. As the wax cools, the solid wax will break away from the glass surface as its volume decreases.

Wax Selection

Wax Type

Candle wax pulls away from the candle glass because the wax contracts slightly as it cools. This is an inherent property of the wax and cannot really be avoided, so most waxes will pull away from the candle glass to some extent. Mineral wax in particular will have poor glass adhesion. Soy wax can have better glass adhesion but will still pull away to some extent over time.

Temperature

Pouring wax at the correct temperature can improve glass adhesion in some cases. However, wax shrinkage is an inherent property of the wax and cannot really be avoided completely, so most waxes will pull away from the candle glass to some extent.

How do I improve glass adhesion?

Clean Jars

Making sure the inside of the glass is clean and free from release agents can help promote adhesion.Most glass is coated in a wax-oil mixture, called cold-coating.This can cause problems for painting and adhesion.

Pre-heating Jars

Pre-heating candle glasses will improve glass adhesion, but this is normally only temporary, and the wax will usually pull away from the glass over a period of hours, days or weeks.

Pouring Temperature

Pouring wax at the correct temperature can improve glass adhesion in some cases. However, wax shrinkage is an inherent property of the wax and cannot really be avoided completely, so most waxes will pull away from the candle glass to some extent.

Room Conditions

The room temperature should be greater than 20° when pouring candles. If the ambient temperature is too low, the wax will cool and shrink more quickly, and pull away from the glass more readily.

Does my choice of glass impact glass adhesion?

Opaque Glasses

Glass adhesion is nothing to be concerned about if you are using an opaque candle glass. Even if the wax does pull away from the side of the glass, this will not normally be noticeable apart from perhaps a slight gap between the surface of the candle and the side of the glass.

Sooting

Why is my candle giving off soot?

Soot is formed by incomplete combustion of candle wax and fragrance oils, leading to formation of carbon deposits. Sooting will almost always occur, but in varying degrees. It is usually emitted when the flame is disturbed, either by airflow, excess fuel delivery or poor wick posture. Excessive sooting can be avoided by experimenting with different wick families and sizes. Some wick families are more compatible with certain wax types.

How high is too high for candle flames?

A 30cl candle would typically have a flame height of around 30-35mm. For a 20cl candle, the optimum flame height would be around 25-30mm. A candle flame can be as high as 75mm, but a flame of this height would probably fail a sooting behaviour test and could also fail a fire safety test.

How much oil should I use?

Different Jar Sizes

The size of candle glass doesn’t impact the percentage of oil used. The same percentage of oil can be used in candles throughout a series of different sizes, although
each differently sized candle will require a different wick.

Different Preferences

The amount of fragrance oil in a candle is decided by the chandler, and is typically based on the cold and hot throw of the candle. Candles containing larger percentages of oil can be more challenging to wick correctly.

Different Waxes

Plant waxes will generally be able to hold more fragrance oil than mineral waxes. Plant waxes can normally accommodate 10 - 12% fragrance oil without difficulty, but the content can be reduced if required. Mineral wax candles can give good cold and hot throw at 8 - 10% but a fragrance content of less than 8% is not uncommon. Candles with fragrance concentrations of more than 14% are very unusual as they can become very expensive.

Wick Selection

The choice of wick will depend on which wax is being used. LX or TG wicks work well with mineral waxes. Stabilo, CL, V, TB, ECO or PGS wicks can be used with
mineral or vegetable blends, while VRL wicks are suited to blends containing a high percentage of plant wax. Overwicking can cause larger flames which can then form larger melt pools and generate more soot. Overwicking is the term used to describe the use of a larger wick than necessary for a particular candle.

sweating

There are two main reasons why a “sweating” effect is observed in candles. Candle “sweating” is sometimes observed in soy wax blends. The sweating occurs when the fragrance leaches from the wax and is usually induced by a temperature change. Sweating can sometimes occur randomly, but it can also indicate that there is too much fragrance oil in the candle. In this case, it may be worth re-making the candle with a lower concentration of fragrance oil. The sweating doesn’t affect the burning performance of the candle.

Sweating can also be observed in some plant wax blends before fragrance is added. This is probably soy or coconut oil from one of the components of the blend and could be related to how quickly the wax was cooled or to the pouring/storage temperatures, perhaps a change in humidity.

Any form of sweating can be removed by gently mopping the sweat beads with a paper tissue. The candle should then burn as expected as sweating does not significantly affect the burning profile of a candle.