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You’ve poured some beautiful candles—they look great, smell amazing, and you’re excited to see them burn. But when you light one and return a while later, you find it burning straight down the center, leaving wax along the sides. This common issue is known as “tunneling,” but there could be more than one reason why your candle isn’t achieving a full melt pool. Let’s explore the possible causes and solutions.
Choosing the wrong wick size is often the first explanation for tunneling, but it’s not always the sole cause. Tunneling from an undersized wick typically becomes evident after several hours of burn time. Here’s how to determine if wick size is the issue:
Testing Burn Time: Allow at least 5 hours of continuous burn time, if not more, to assess whether the wick is capable of creating a full melt pool. If, after 5 hours, the wax remains unmelted around the edges and the melt pool does not extend across the entire diameter, the wick may be too small.
Adjusting Wick Size: If there’s only a thin layer of wax left on the sides, you may need to increase the wick size by one level. However, if the wax is thicker, consider going up by two wick sizes and conducting another test burn.
An undersized wick can lead to an insufficient melt pool and a weaker scent throw, so adjusting the wick size is crucial for optimal performance.
Air pockets are another, often overlooked, cause of tunneling and can be harder to detect until they disrupt the candle’s burn. When air pockets are trapped beneath the surface, they can cause the wax to melt unevenly, leading to a sudden drop in the melt pool and rapid wick burn-down. Here’s what to look for:
Signs of Air Pockets: If you notice cracks on the surface of your candle before burning, these may indicate air pockets beneath. When the candle burns and reaches these pockets, the wax can suddenly collapse, forming a deep hole in the melt pool. This results in tunneling and a small flame, as the wick quickly burns down to meet the lower level of the melt pool.
Identifying an Air Pocket Issue: If tunneling is accompanied by a sudden and deep hole in the wax, it’s likely due to an air pocket. In comparison, an undersized wick would take several hours to create such a deep melt pool, whereas air pockets cause an immediate drop in the surface level.
Air pockets form when wax cools too quickly, often due to low pour temperatures or a cold room environment. Here’s how to prevent them:
Pour Temperature: Pour your wax 5-10 degrees hotter than usual, especially during colder months, to ensure a gradual, even set. Higher pour temperatures allow the wax to settle smoothly and reduce the risk of air pockets.
Room Temperature: Keep your workspace at a moderate temperature, as cold air can cause the candles to cool too quickly. Ideally, candles should cool and set from the bottom up. If the room is too cold, the wax may start setting from the sides or top first, trapping air beneath the surface and leading to hidden pockets.
Understanding the root cause of tunneling can help you make the right adjustments to your candle-making process:
Wrong Wick Size: If your candle burns narrowly down the center after 5+ hours, it’s likely due to an undersized wick. Test by wicking up one or two sizes and retesting.
Air Pockets: If your candle suddenly forms a deep hole in the melt pool shortly after lighting, air pockets may be the cause. Adjust pour and room temperatures to prevent this issue.
By identifying and addressing these factors, you can achieve a full, even melt pool and a better scent throw in your candles. Remember, testing and refining your process is essential to creating candles that burn smoothly and beautifully.
