If you’ve ever poured a candle that looks perfect on the outside but develops a mysterious crater or cavity around the wick as it cools, you’ve hit the classic sinkhole problem. Don’t worry—this is one of the most common issues in candle making and is easy to fix once you understand the science behind it.
What Are Sinkholes?
A sinkhole is a cavity or deep dip that forms in the center of a candle as it cools. They usually appear right around the wick and can range from shallow surface dips to deep, hidden air pockets beneath the surface.
While they can ruin a smooth top, sinkholes are just a natural byproduct of wax contracting, not a sign that your formula is broken.
Why Do Sinkholes Form?
Wax naturally expands when heated and shrinks as it cools. Sinkholes happen when that shrinkage occurs unevenly. The primary culprits include:
- Rapid Cooling: Cooling candles too quickly forces the outer edges to solidify first, trapping shrinking air pockets in the center that eventually collapse.
- Pouring Temperature Issues: Pouring too hot causes extreme shrinkage and uneven cooling. Pouring too cool traps air bubbles before they can escape.
- Container Shape: Deep or narrow jars trap heat differently than shallow, wide ones, which impacts how evenly the wax cools.
- Wax Type: Natural waxes (especially soy) contract significantly more than paraffin as they set, making them highly prone to sinkholes.
How to Fix and Prevent Sinkholes
Even experienced candle makers deal with sinkholes, but they are incredibly easy to resolve with these standard techniques:
1. Do a Second Pour (Top-Off Pour)
For deep cavities, save a small amount of your original wax batch. Once the candle sets, reheat that leftover wax to about 10°F to 15°F hotter than your initial pour temperature. Carefully pour just enough to fill the hole and level out the surface.
2. Use a Heat Gun
For shallow surface dips, use a heat gun on its lowest setting. Gently sweep it over the top of the candle until the surface melts just enough to self-level and fill the gaps.
3. Tap the Containers
Immediately after pouring your candles, lightly tap the sides of the jar or tin on your work surface to help trapped air bubbles rise to the top before the wax sets.
4. Control Your Cure Environment
Cool your candles in a draft-free room kept around 68°F to 75°F. Avoid placing them near open windows, fans, or AC vents, as fluctuating temperatures cause uneven cooling.
Pro Tip: Use a Wick Centering Tool because the wax around the wick is the last to cool, it is the most vulnerable to pulling away. Using a dedicated wick centering tool or wick bar keeps the wick perfectly straight, ensuring even heat distribution as the core solidifies.
