What is frosting?

Frosting (also called blooming) is an informal term for a mild type of polymorphism. This word is derived from the Greek words "poly" (many) and "morphe" (form), and it refers to when the wax exists in different crystalline states at once. Polymorphism ranges from light frosting on the surface of the candle to large bumps and cavities in the candle.

When does frosting occur?

Frosting only impacts plant-based waxes. Soy and rapeseed waxes are particularly prone to frosting. That being said, frosting is highly unpredictable and can occur at any time during the candle-making process. It may even be the case that in the same batch, some candles frost while others do not.

How do I minimise frosting?

Find the right cooling profile.

Getting the right cooling profile can help, but frosting is frequently unavoidable. To minimise the risk of frosting, experiment with your cooling temperatures. The right temperature will depend on your fragranced wax mixture.

Blend with paraffin

Frosting only occurs with plant-based waxes. Therefore, using plant and mineral wax blends substantially mitigates the risk of frosting.

Pour at the right temperature

Our general recommendation would be to pour your plant wax candle as close to the congealing point as possible, which is the temperature at which your wax becomes cloudy. This temperature varies from wax to wax but getting it right will help your candle to solidify faster.

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.

How do I prevent candles from mushrooming?

Minor clubbing is very common and is not normally a cause of concern. More pronounced mushrooming is often a sign that a candle is overwicked, so down-wicking will reduce fuel flow and should 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. Most wick families have differing chemical treatments, or constructions, which are suited to different candle systems. For example, LX wicks are best suited to paraffin candles with moderate scent loads, whereas V wicks are designed to deal with heavy fragrance loads.

Occasionally, a particular fragrance oil will cause clubbing regardless of the wick used. In such cases, a different wax blend may improve the situation. Candle Shack's fragrance oils are developed by expert perfumers for use in candles, but fragrance oils from other suppliers may not be compatible with candle making.

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.

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 dust and grease can help promote 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.

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.

What is sweating?

In candle making, sweating refers to beads of liquid oil appearing on the surface of a candle. It is caused by the expansion and contraction of wax crystals, which can squeeze oil out of the body of the wax, making it visible on surfaces.

Why does sweating occur?

There are five main reasons why a candle may have liquid on the surface. The first is that there may simply be too much fragrance or essential oil mixed into the wax. This means that there is insufficient space between the crystals to retain the amount of fragrance oil added.Second, sweating may be a characteristic of the wax itself. Many plant waxes are a blend of fully and partially hydrogenated oils. If cooled incorrectly (too slowly), low melt point ‘alpha’ crystals can form and sit on the surface of the wax as a liquid or slurry. These fat oils can also displace fragrance oils, as there is insufficient space for additional liquids amongst the crystals.Third, rapid changes in temperature can cause sweating, especially when moving a candle from a cold location to a warm location.This can also happen if the oil is added when the wax is too cool, or if the wax/oil is not properly mixed. In this instance, the wax and oil do not form a homogenous mixture and the distribution of fragrance will vary throughout the candle.Finally, if the fragrance supplier has little experience in candles, their fragrance oils may contain components that are insoluble in your wax. This can be the case when fragrances were developed for other products (i.e. cosmetic products), as fragrances rarely work well in multiple products and should be fine-tuned for the end application.

How to avoid sweating?

- Fragrance load reduction

One of the first steps you can take is to check the wax manufacturer’s fragrance load recommendation. This will be unique to every wax type. As a rule of thumb, however, we would recommend keeping your fragrance load to 6-10%, although some fragrances can be added at up to a 12% load in waxes. Experimentation and testing are key.

-Buy quality fragrance oils, optimised for candles

All Candle Shack oils are developed primarily for use in candles and are subjected to rigorous stability and performance testing. Be cautious if buying fragrance oils that are provided by generalist craft supply businesses, claiming their oils work well in candles, soaps, bath bombs, carpet fresheners, face creams etc. It is extremely unlikely that they will have been properly tested, if at all; especially if they have hundreds of oils.

- Temperature control

Keep a moderate and constant temperature during storage and avoid prolonged storage at elevated temperatures. As a general rule, we would recommend storing your candles at a temperature of 18°C to 25°C. Likewise during production, allowing plant-based candles to cool at ambient temperature will minimise separation vs. attempting to slow the rate of cooling too much.

- Switch waxes

Fragrances react differently and have different solvability in different waxes. By switching waxes, you can try to find one that works well with your chosen fragrances.

What are jump lines?

Jump lines (also known as chatter or stutters) are thin rings or horizontal lines that form along the outer edge of container candles and pillar candles.

Why do jump lines happen?

Jump lines only occur with paraffin wax as it has a higher melting point than plant waxes. When hot paraffin wax (usually at 65°C to 70°C) is poured into room temperature glasses, it solidifies very quickly along the edge of the jar, even as more wax is still being poured on top of it. This then forms jump lines.

How do I avoid jump lines?

Choose opaque candles

While they are not aesthetically pleasing, jump lines do not impede candle performance. Therefore, avoiding clear candle jars and choosing opaque ones will hide any jump lines.

Pre-heat candle jars

We recommend heating your candle glass jar to 40°C to 45°C before pouring to prevent jump lines from forming.

Increase the pouring temperature

When using paraffin wax, heating the fragranced wax by 5°C to 10°C more than its melting point will help to avoid jump lines.

What is tunnelling?

Tunnelling is an extreme form of hang-up, where a thick coating of wax remains on the side of the container candle glass as the candle burns down.

What causes tunnelling?

Tunnelling 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.

What are sinkholes and cavities?

Sinkholes and 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 because of the contraction of the wax as it cools and changes from liquid to solid. Cavities are more common in plant wax because of polymorphism (changes in the crystal structure of the solid wax as it cools).

How do I avoid sinkholes?

Double Pour:

The risk of sinkholes in a finished candle can be reduced by using the double-pouring technique. First, fill 70-90% of the candle. After cooling, when the wax has contracted, the second pour fills the candle to the desired level.

How do I fix candles with sinkholes?

Relief hole:

A relief hole can be created by puncturing the wax above a sinkhole after the first pour of the candle. The void can then be topped up with melted wax. This is similar to the double-pouring technique.

Heat gun:

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

What are sinkholes and cavities?

Sinkholes and 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 because of the contraction of the wax as it cools and changes from liquid to solid. Cavities are more common in plant wax because of polymorphism (changes in the crystal structure of the solid wax as it cools).

How do I avoid sinkholes?

Double Pour:

The risk of sinkholes in a finished candle can be reduced by using the double-pouring technique. First, fill 70-90% of the candle. After cooling, when the wax has contracted, the second pour fills the candle to the desired level.

How do I fix candles with sinkholes?

Relief hole:

A relief hole can be created by puncturing the wax above a sinkhole after the first pour of the candle. The void can then be topped up with melted wax. This is similar to the double-pouring technique.

Heat gun:

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

How do I avoid cavities?

Pouring temperatures:

Cavities can be avoided by pouring candles at recommended pouring temperatures.

How do I fix candles with cavities?

A heat gun can be used to melt the wax around the cavity and fill the cavity with liquid wax

What is cracking?

Cracking is often experienced when using plant-based waxes. Cracks can appear on the surface or throughout the candle.Cracks can appear in different forms. Sometimes cracks occur as shallow localised cracks that form a rough circular shape on the surface of the candle. These cracks often appear above a cavity in the wax. Occasionally, radial cracks can form across the top of the candle, running from one edge to the other and normally passing through the wick area. Radial cracks can be deep, often running from the top to the bottom of the candle.

Why does cracking occur?

As the wax cools, it goes through different stages of crystallisation. During those phases the wax can contract and crystallise in different ways, causing cracks to occur. Cracking is a common problem in plant wax candle making, with rapeseed wax being more prone to radial cracks. Soy wax, while less likely to crack, tends to produce circular or radial cracks. If candles are allowed to cure in cool environments, they are more likely to crack.

How to avoid cracking?

Temperature control

Keeping adequate and consistent pouring, cooling and storage temperatures is the best way to avoid cracking. Make sure you pour your wax mixture at the temperature recommended by the wax manufacturer. While your candles are cooling, ensure that they are not kept in a cold environment. As a rule of thumb, we would recommend cooling your candles at a steady temperature of 18°C to 25°C for 48 hours. After that, the candles can be kept at slightly cooler temperatures.

Paraffin blends

As cracking is predominantly a plant wax issue, you could choose to blend your plant wax with paraffin wax or switch to paraffin wax only.

How to fix cracking

Surface cracks can often be removed by using a heat gun for a few seconds to smooth out the cracks. Deeper cracks can also be removed by using a heat gun but they may reappear as the candle cools again.

What is hang up?

In candle making, hang up refers to a thin coating of wax that hasn’t melted and is left on the inner wall of a container candle as the candle burns down.

Why does hang up occur?

Hang up occurs because the heat of the flame isn’t sufficient to melt enough wax to give a full melt pool. This is usually because the candle is under-wicked, but occasionally a fragrance oil may not be compatible with a particular type of wax, and the flame can die off over time, causing hang up. If the outside surface of the candle glass gets too cold, the heat from the flame might not be sufficient to wax may not melt in this region, again causing hangup.

How is hang up different from tunnelling?

Tunnelling occurs when the flame of an underwicked candle isn’t strong enough to give a full melt pool (FMP) and a “tunnel” develops down the middle of the candle, leaving a residual coating of wax on the inner wall of the candle. Severe hang-up and mild tunnelling are effectively the same thing.

How to avoid hang up?

Temperature control
One way to avoid hang up is to keep a warm ambient temperature in the room where you burn your candle. As a general rule of thumb, we would recommend a temperature of 18°C to 25°C.

Change the wick
Hang up can usually be avoided by choosing a suitable wick for your candle, so it’s always worth experimenting with different wick families and sizes. The basic procedure is to increase the wick size until hang up doesn’t occur. However, be careful not to pick a wick that is too big as this will increase the risk of sooting, so finding the right balance between hang up and sooting is the key.

Add paraffin
Hang-up is more common with plant-based waxes than with paraffin waxes, as paraffin waxes are more ‘cohesive’ due to their long-chain hydrocarbon molecules. This means paraffin waxes tend to stick together, whereas plant waxes can break apart, leaving residue on glassware. So, adding paraffin wax, will result in a more ‘cohesive’ blend that is less likely to leave residue on the glass or hang up.

What does “no hot throw” mean?
The “throw” of a fragranced candle refers to the perceived intensity of the fragrance. “Cold throw” refers to how a candle smells when unlit, and “hot throw” refers to how a candle smells while it is burning. When a candle is described as having no hot throw or a poor hot throw, this means that the scent is much weaker than expected while the candle is burning.


Why does a candle have no hot throw?
Varying perceptions
There are multiple reasons for a candle to be perceived not to have a hot throw. First, it’s important to note that everyone perceives smells in different ways. What may smell powerful to one individual may seem weak to another.

The wax
Another reason for not having a good hot throw may be the wax itself. As a general rule, paraffin wax gives a better hot throw than plant wax. This is partly because paraffin wax candles have higher melt pool temperatures and fragrance oils.

Incompatible wax and fragrance
Occasionally, your chosen blend of wax and fragrance oil may not be compatible. Fragrance oils will mix, perform and interact differently in different waxes. Some mixtures simply don’t throw well. Different types of plant waxes can affect the hot throw performance of a candle. You may find that a particular fragrance oil has poor hot throw performance in a soy wax but a good one in a rapeseed wax or vice versa.

Fragrances unsuitable to candle making
Many fragrance oils are simply not suitable for candle making and will never give a good hot throw. Candle Shack works with expert perfumers to ensure that our oils will give the best possible hot throw experience, but oils from other general suppliers may not be developed to the same high standard.

Fragrance content
Poor hot throw can also be caused by a low fragrance content in the candle. There may simply not be a high enough percentage of fragrance in your wax.

Unsuitable wick
Poor scent throw can sometimes be related to the type of wick used. Performance can often be improved by experimenting with different wick families.


How to avoid making a candle with no hot throw?
Candle Shack recipes
One way to make a candle with a powerful hot throw is to follow one of Candle Shack’s recipes as they have been specifically designed and tested to have strong scent throws. However, remember that everyone perceives scent throw differently – our testing panel have approved these recipes but they might not work for everyone!

Increase the fragrance content
Experimenting with your fragrance content could help. A typical content for paraffin waxes is 8%, and for plant waxes it is 10%, but these percentages can be increased if desired. The maximum permitted amount of fragrance oil in candles as per your scent's IFRA conformity certificate is usually very high. However, even if you increase the fragrance content, you should still test your candle for hot throw. A higher fragrance load may not always improve the hot throw.

Test your candles
Always test your candles before selling or gifting them to make sure that you are happy with their scent throw (and their safety). Burn the candle until you have a full melt pool and then assess how it smells. Feedback from a panel of different people will give you a more meaningful measure of the hot throw.

Use high-quality fragrance oils
Try to avoid using fragrance oils that haven’t been specifically developed for candle making, as this can often lead to extremely poor hot throw performances. By using Candle Shack’s fragrance oils, you can be sure that the oils have been selected and approved by our R&D team and our fragrance testing panel.

What is bridging?

When a wick doesn’t self-trim sufficiently as the candle burns, the extended length of the wick may curl up to the point where the end of the wick touches the melt pool. This situation is referred to as bridging since the curved-up wick loosely resembles a bridge.

What are the consequences of bridging?

Sometimes a bridging wick can curl into the melt pool to such an extent that the wick becomes submerged in the liquid wax and self-extinguishes. However, bridging can occasionally create a hazard. Bridging itself will not cause a candle to fail a fire safety test but if a wick bridges and remains above the melt pool, the flame can increase in size and the rate of wax consumption may increase. In extreme cases, the flame height could be greater than 75mm and the candle would fail to meet the safety standard. A larger flame could also make the container so hot that it cracks. A larger flame will also generate more soot.

Why does bridging occur?

Bridging occurs when the chemical treatment on the wick is not compatible with the chosen wax and fragrance combination. Chemical treatments on wicks are intended to aid combustion and allow the wicks to self-trim, so if an incompatible wick is used, the wick may not self-trim and could start to bridge.

How to avoid bridging

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What to do when a candle is bridging:

If you are trying to find the best wick for your candle and you notice that your candle wick is bridging, try different wicks as described above. If you are burning a candle and the wick isn’t self-trimming, we recommend trimming the wick manually every few hours or so to avoid creating a full bridge or an excessively large flame.

What is aftersmoke?

Aftersmoke is the time that the wick visibly smokes or glows after blowing out a candle at the end of a burning period. The aftersmoke will probably be slightly different for each burning period as your candle burns down. Wicks can often smoke or glow for longer at the end of the first burn period than for the rest.
The aftersmoke for a candle should be calculated as an average of the aftersmoke for every burn period of the candle. The average aftersmoke time should not be more than 30 seconds.

Why does aftersmoke happen?

When the candle is extinguished, the wick can continue to smoulder, especially if there are carbon deposits present, which are often seen as a "mushrooming" at the tip of the wick. This smouldering is the result of the wick consuming the remaining combustible materials in its vicinity, even without an active flame. This produces the visible smoke known as aftersmoke.

How to avoid excessive aftersmoke

- Reduce clubbing
Aftersmoke can be linked to clubbing/mushrooming, so if your candle shows excessive clubbing, we would recommend reducing your wick size or changing wick families to reduce aftersmoke and clubbing.

- Change fragrances
Sometimes, a longer aftersmoke may be an inherent characteristic of the fragrance. As long as the average aftersmoke time does not exceed 30s, your candle will meet the standard for aftersmoke. If aftersmoke goes on for too long, however, we would recommend changing fragrances and choosing one that is specifically optimised for candles such as Candle Shack's.