Wet Spots in Candles (Adhesion)
Adhesion describes how well wax holds on to a container surface. Containers range from glass and aluminum to ceramic or cement. Candle makers generally require the ability for wax to remain in contact with the container surface to fill as much of the container volume as possible. The candle industry sometimes calls adhesion problems “wet spots” because it appears moist anywhere the wax pulls away from the surface.
Wet spots are primarily cosmetic, but extreme cases can cause the candle to fall out of the container when tilted without a lid. Candles created for decoration or without a container naturally don’t require strong adhesive properties to function.
Wax manufacturers design wax blends with additives to strengthen this behavior, as advertised by suppliers of that wax.
Causes of Wet Spots
Wet spots occur when wax pulls away from the container edge. The science is relatively simple: wax expands when it heats up and contracts as it cools.
Candle making involves melting wax into a liquid (expansion) then pouring it into a container where it cools down (contraction). The most dramatic volume change happens right after pouring the candle.
Candles usually go through “micro” temperature changes throughout their life. Anytime the temperature changes, candle wax risks pulling away from the jar sides. This can happen during curing, shipping, and storing the candle, and preventing it is nearly impossible.
Adhesion problems are completely unavoidable since their cause is primarily due to changes in the environment. Unless you have some sort of magical control, your best option is to prepare candles with strategies and materials resistant to wet spots. Read more below.
Treatment
It’s impossible to prevent wet spots, but there are a few things you can do to mitigate issues:
- Clean containers prior to pouring wax
- Pour at cooler temperatures while also preheating the container with a heat gun
- Select wax known for great adhesion
- Optimize storing and curing conditions to limit temperature fluctuations
- Ship candles with ice packs in an insulated chamber
Clean containers ahead of time using dish soap and/or white vinegar followed by a hot water scrub. Make sure the jar is completely dry before pouring any wax by resting them upside down on a towel or blasting with a heat gun to accelerate the drying process. Moisture in the container is a big no-no in candle making because it impacts more than just appearance!
Pouring at a cooler temperature into a pre-heated container reduces the temperature difference between the wax and jar. Sides that are too cool will cause differential cooling – the sides will cool faster than the top or middle which can introduce poor adhesion too.
Most wax on the market will brag of great adhesive properties. Wax manufacturers work on balancing the right amount of additives to help performance and sometimes base their recommended pour temperatures on this as well.
If you have any questions of whether a specific market wax has problems with adhesion, ask the community or find other candle makers that are familiar with that wax. Sometimes blending waxes creates more problems than not if the additives interact with each other in unexpected ways. As always, learn these behaviors through robust testing.
Candle wax is sensitive to temperature changes, fluctuating a significant amount when the thermometer changes. Creating an optimal pouring and curing environment is a huge win against adhesion problems, but only represents the beginning of a lifelong struggle. Anytime temperature changes the candle risks losing adhesion so more stable environments are ideal.
Final Recommendations
Heat guns can remove wet spots, but this often creates more problems than it solves. Concentrated heat on the spots will melt the wax enough to fill in the voids again and send the air to the top.
Unfortunately, such a dramatic change in temperature creates a chance more adhesion or frosting issues can happen. Since wet spots are only cosmetic and don’t impact performance, it’s better to leave them be.
Customers usually don’t care about or even notice them – this is a candle makers bane. Pick up most any common candle at a store and you’ll see wet spots prevail! Don’t lose any sleep over adhesion problems on your candles – they are merely distractions to the rest of your process. Even if you could control the environment, they usually find a way to appear during transportation, shelf-life, or in the customer’s care. Focus on creating safe, high performance candles instead.
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