How to Troubleshoot & Fix Sinkholes in Candles.

What causes a sinkhole? How do you prevent one? And what do you do if you get one? Let's take a look.

What Causes Sinkholes?

A sinkhole is caused simply by your wax shrinking as it cools. Your wax is going to shrink as it cools — that's what happens when molecules are moving around freely when they're hot, and then start to move closer together as they cool. The surface of your wax is probably the first thing to cool because it's exposed to air, while the base and core of the candle is still warm and shrinking, pulling from the top of the jar.

Paraffin vs. Soy

With paraffin blends, you don't typically get sinkholes the same way. Paraffin has flexibility which means as it cools and shrinks, the surface flexes with it. That's actually why our Pro-Flex wax is named Pro-Flex. With paraffin, you can simply hit it with a heat gun to level it out, or pour it cooler after warming your jar first to reduce the amount of shrink.

Soy, on the other hand, is very rigid in its crystal structure. Because it's so rigid, the top cools first and acts as an insulated cap. As the wax shrinks inside, it pulls and pulls but the top surface says "I am not moving, I am not flexing." So eventually it breaks, lets air in, and creates a sinkhole.

How To Prevent Sinkholes

Interestingly, both pouring cooler and pouring hotter can help.

Pouring hotter, around 170°F, helps eliminate air bubbles that get caught in the wax. Air bubbles contract as the candle cools and cause pulling, which leads to sinkholes. At 170°F, air bubbles can escape the jar naturally before getting trapped against the sidewall or top. Pouring at 170°F also allows the wax to bring the jar itself up to an equal temperature before crystallization begins, which reduces uneven cooling.

For thinner sidewall jars, pouring at 135°F or above will do the trick. For thicker sidewall jars, you'll want to pour a little hotter.

Pouring cooler, below 120°F, is the other option. When the wax reaches a hazy, crystallizing stage, it has already done much of its shrinking before it goes into the jar, which reduces sinkholes.

Avoid pouring between 120°F and 135°F,  that's the zone where you're most likely to run into problems.

How To Fix a Sinkhole

If you do get a sinkhole, you can fix it. Briefly hit the top with a heat gun to smooth it out — but don't overdo it. When you run a heat gun over the top of a candle, the fragrance on the surface evaporates into the air, which is exactly why you can smell it so strongly. That fragrance is leaving your candle, so keep it quick.

After smoothing the top, gently wave your hand or any flat object over the surface to create a little airflow. This causes the very top layer to begin crystallizing quickly, giving you a smoother, more even finish.

Sinkholes are a common problem, but with the right pour temperature and a few simple techniques, they're very preventable and very fixable. Let us know if you have any questions!