Candle Curing for Beginners
Candle curing describes the period of time from when a candle is poured to when it finally burns.
Seems relatively innocent, right?
The truth is that certain wax types require a specific curing period to ensure optimal performance.
There’s no argument that curing is necessary, but the amount of time a candle needs before it’s “ready” varies depending on a lot of factors – including opinions on the matter.
In this guide you will learn:
- The science behind candle curing
- Why curing is necessary
- How long to cure your candles for
At the end is a table with suggested cure times for your wax.
The science behind candle curing
Two things happen after pouring a candle:
- Wax hardens into a semi-solid.
- Fragrance oil “binds” to the wax.
Let’s break these down individually.
1. Wax hardens into a semi-solid
Candles are a semi-solid structure, contrary to common belief they are solid.
Fragrance oil is a liquid at room temperature. This doesn’t change just because it’s in a candle, therefore the entire structure of a candle is part solid (wax), part liquid (fragrance) – a semi-solid.
Wax cools into a solid after pouring the candle.
Cooling leads to hardening, and some waxes continue to harden long after the pour.
“Vegetable waxes”, like soy, continue to harden their entire life because they’re polymorphic. Crystals continue to form in the wax in response to time and temperature leading to a harder wax over time.
Other waxes, like paraffin, reach almost full hardness within a day or two of pouring.
Part of candle curing is the continual change of a wax after the initial cooling.
Harder and stiffer wax requires more thermal energy to melt.
Sometimes this change can be substantial enough that a wick that performs well in the first two weeks might be too small beyond that time.
Conversely, softer wax melts easier.
Burning a candle too soon may yield false results since it requires less heat to melt wax in the first 48 hours compared to later.
2. Fragrance binds to the wax
The second major component of candle curing is binding fragrance oil to the wax.
Many candle makers assume mixing fragrance oil and wax creates a new substance, but this isn’t true.
Fragrance and wax don’t chemically react with each other.
You need a degree in organic chemistry to understand what happens when blending fragrance and liquid wax, but figuring it out is still difficult for a few reasons.
First, every wax has a different design.
Most commercial candle wax contains different additives of various compositions, and almost all blends are proprietary.
Fragrance oil is equally mysterious, having almost zero public information about the ingredients.
Second, the large variety of wax and fragrance available on the market further complicates this chemical equation, however we know a few things about what happens when blending:
- Wax expands when it turns into a liquid and contracts as it cools into a solid. This phenomenon is responsible for “wet spots” in container candles.
- Fragrance and wax will mix as liquids without chemically changing their compositions. Fragrance oil is still fragrance oil. Wax is still wax.
- Cooling wax traps fragrance oil molecules in its structure while turning into a solid.
- The “aromatic” molecules spread out while the wax hardens over time.
Excess oil tends to pool in the candle if it contains poorly mixed fragrance, or there’s simply too much in the wax.
Candle curing is the process of continuous hardening of wax to disperse fragrance oils evenly throughout the blend.
Different wax and fragrance oil combinations may require more or less time to achieve an optimal state.
Is curing necessary?
The unofficial debate in the candle making community centers on how long candles need to cure before they’re ready.
Most candle makers decide a candle is good based on criteria that is measurable, and criteria that isn’t.
But usually it’s based on the criteria that’s harder to quantify. All said and done there’s three items curing impacts:
- Scent throw
- Hardness or stiffness
- Whether or not the candle can be used
Let’s break each of these down.
Scent Throw
Ask anyone to smell a candle and their opinion of how strong it smells (and what it smells like) might vary from anyone else you ask.
Despite scent being our strongest sense, fragrance is a very subjective topic.
Aroma can technically be measured with gas chromatography-olfactometry, but most, if not all, candle shops lack the equipment and willingness to take on such a task.
Smaller candle operations tend to use a subjective rating scale across a variety of different people, friends, or relatives and use the aggregate “opinion” of the smell to figure out if it’s strong enough.
The complicated system for measuring scents spills over into the debate on curing because hot throw is the usual metric for candle design.
Most people judge a candle entirely on the scent throw given by the first burn. The results for this vary wildly depending on the candle and the creator.
Although it’s entirely possible to achieve a strong hot throw on a candle that cures only 24 hours before burning, this doesn’t mean the candle shouldn’t cure longer.
In fact, this behavior potentially broadcasts false information about a candle’s safety…
Hardness
Polymorphic hardening of “natural” waxes is a scientific fact.
A soy candle poured on Monday will be harder on Sunday than it is on Tuesday or Wednesday.
Harder candles potentially require larger wicks to generate enough heat to melt the wax.
Burning this candle on Tuesday may lead one to believe the wick is oversized if the wax melts too quickly, but waiting longer would give different results.
Vegetable waxes continue to harden over the course of their life.
A lot of the candle making community believes the most hardening occurs within the first 14 days after pouring, but changes like that continue for weeks to months after pouring as well.
More stable wax, like paraffin, notably doesn’t change much 24-48 hours after pouring. Candle makers don’t need to exercise as much patience between iterations of their designs.
Going back to scent throw for a second, lighting a candle while it’s still curing might create a wider and deeper melt pool which could be evidence the hot throw is very strong.
Give that same candle another week and the melt pool may not develop so quickly now that the wax is harder.
Burning too early in a candles curing time can muddy the true results.
Whether or not the candle is ready for use
The primary criteria for accepting a candle design should be:
- Does the candle pass all safety tests?
- Are the cold and hot throws appropriately strong?
Some candle makers get so caught up on the scent they forget to truly burn test their candle.
Depending on the wax, the results could vary depending on how long the candle cured for.
Burn testing is not an overnight activity.
It can take a week or more depending on the testing framework in place. The rubber meets the road in testing – no matter how good a scent throw is, the candle still needs to perform well in other areas that are much easier to measure.
Testing can also expose the curing patterns for a particular candle.
For example, if a candle is burned for 4 hours one day after being poured but wasn’t substantially cured there will be evidence in subsequent burns.
The middle generally hardens last, and the later burns will reveal how much softer it is in the middle compared to the outside.
It can easily be misdiagnosed as tunneling, but is actually from not curing long enough.
How long should you cure your candles?
Typically, longer cure times are better.
Why?
Most people burn their candles irregularly, leaving them un-burned for weeks at a time. Depending on your wax, your wick test may be misleading if your first burns happen before the suggested cure time for your wax which can impact candle safety.
Suggested times are rules of thumb. They aren’t scientifically derived, but rather the collective opinions of many candle makers over the years.
Your mileage may vary.
Final thoughts
Most candle makers would prefer a shorter cure time, but this is a symptom of impatience.
In reality, most candles created for others will not be burned in the first 24 hours, regardless of cure time.
Add to that the length of time it takes to burn test, which can sometime take weeks.
Even if a candle throws well the first couple burns, if it peters out and fails to generate anything worthwhile later it’s a failed design.
Although some candles end up in customer hands very quickly, most candles suffer from a bout of shelf life.
Shelf life is a good reason to postpone burn testing until the minimum time before a customer has the candle to ensure results reflect real life use cases.
Doubly true for vegetable wax, which continuously changes throughout its life.
The general rule of thumb for testing soy wax is 1 – 2 weeks, but as close to 2 weeks as your patience allows. Also consider that each lot of wax is different given the variability in soybeans, which can radically change curing behavior at times.
Curing is also directly impacted by the fragrance oil in the design.
Some FO is designed for use in all wax while others are brought to market as-is. The various properties of fragrance directly impact the performance in binding capabilities in different wax types.
Some fragrances may take longer to bind with certain waxes, requiring a greater curing period.
Regardless of what you believe the right answer is for curing, testing is the ultimate standard for safety and performance.
