What causes sink holes in candles and how to prevent them

Sinkholes are small pockets of empty space that can sometimes form within candle wax when it hardens. These cavities tend to dip down toward the centre of your candle. It’s important to find and fix sinkholes because they can negatively affect how the candle burns. 

WHAT CAUSES SINKHOLES? 

Sinkholes sometimes form during the wax setting process, when candle wax at the edge of the jar and around the wick cools down at a faster rate than the rest of the wax in the container. 

So how does that result in a sinkhole?

When wax is heated it expands. Conversely, as wax cools down, it shrinks. When melted candle wax is poured for the first time, the heat causes it to expand and fill up the container.

As the wax gradually cools down and shrinks back to its solid state, it does so faster at the edges and around the wick. So, imagine the liquid wax starting to harden and "sticking" to the edge of the candle jar and the wick. 

Meanwhile, the still-cooling liquid wax under the surface that's not touching the edge of the jar, or the wick continues to shrink and dip down, eventually forming a cavity as it hardens. 

And voila, a sinkhole.

DOES TEMPERATURE AFFECT SINKHOLES?

During the candle-making process, it’s not just the temperature of the wax that’s important to take note of, but also the temperature of the workspace and the temperature of the candle jar being used.

The temperature you should pour your wax at depends on the type of wax you are using. For example: 

Soy Wax (120-165 F)

  • Paraffin Wax (160-180 F)
  • Beeswax (155-160 F) 

 Some candle makers use a method of pouring the wax at cooler temperatures (e.g., around 120-135 F) to help prevent sinkholes, since cooler wax tends to melt at a more even rate. 

The temperature of your workspace should ideally be around 70 F. Work in a ventilated area without any extraneous air movement such as drafts or breezes. 

Lastly, the temperature of the candle jar being used can also affect how quickly or slowly the poured-in wax cools. For example, a cold jar causes wax near the edges to cool even faster, contributing to sinkhole formation. 

Ideally, you should set your candle jar in an open area with enough time for it to naturally reach room temperature.

DOES WAX TYPE AFFECT SINKHOLES?

The type of wax used in your candle can also affect the likelihood of sinkhole formation. That's because different wax types have different melting points, and some shrink more than others as they cool. Paraffin wax in particular is notorious for creating sinkholes. 

DOES THE SIZE AND SHAPE OF THE CANDLE JAR AFFECT SINKHOLES?

Yes, the probability of sinkholes changes based on the size of the jar or vessel you use. 

 

  • Wide and shallow vessels typically have a low likelihood of sinkholes forming. 
  • Wide and tall vessels have a moderate likelihood of sinkholes forming.  
  • Narrow and tall vessels have the highest likelihood of sinkholes forming.

 

HERE'S WHY SINKHOLES IN CANDLES ARE BAD!

Besides the unattractive look of sinkholes, it’s important to get rid of them because they negatively affect wick function. when you burn a candle, the wick behaves like an absorbent towel. It sucks wax upward into the flame.

As your candle melts down to the level of the sinkhole, all of the sudden a large amount of wick is exposed. 

When an excessive amount of wick is exposed, way too much liquid wax is sucked upwards, creating a dangerously large flame. 

HOW TO FIX SINKHOLES IN CANDLES

Sinkholes are relatively common, especially when making candles at home, but they're usually pretty easy to catch and fix. 

It's quite rare to purchase a candle from a reputable brand and discover a sinkhole in it since professionals have quality checks in place during the manufacturing process to prevent or fix them. 

But in the unlikely event that you discover a sinkhole in a candle that you bought, here's how to fix it.  

 Hold a heat gun (a hair dryer also works) over the top of your candle to melt the surface. 

  1. As the wax starts to melt, poke at the sinkhole with a chopstick (or a similarly shaped object) to determine the size of your sinkhole. Sometimes, what looks like a tiny hole can actually be a lot bigger under the surface.
  2. Puncture the wax to allow melted wax to fill the open cavity.
  3. Once the cavity is filled and the surface of the candle wax is nice and flat again, allow your candle to cool back down to room temperature. 

Find out how to fix tunnelling here.

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