How to Test Fragrances in Candles

London with Particle Goods started making candles in 2017 and now sells them across the country. We asked her to put all our fragrance oils in candles and share her results. Below, she goes over how to choose a wick, how to test scents, and how to analyze the results.

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Before you start selling your candles, or making large batches of them, it’s a good practice to test all your materials together. A basic testing strategy can take a little work to set up initially, but it will save you time and huge headaches in the long run.

It’s crucial to test any new fragrance or variable you introduce (like a new container, candle dye, etc.) to your product and never assume that it will work perfectly. So how do you navigate the testing process?

The best way to do this is to start with a baseline test. It’s a good idea to use consistent containers for your candles so that you don’t have to go through additional tests often. Begin by choosing your container and wax blend. The next variable we need to solve is wick size.

If you don’t know what size (or brand) wick will work best with your container, I would start by looking at the wick charts provided by the manufacturer or supplier. I like to test at least 2-3 wick sizes from the same brand, so if you’re hoping to try multiple brands, keep in mind that this helps us narrow in while allowing for other variables. 

For this first test, I recommend not using fragrance oil. Once we have a better idea of what wick size you think will work best, you can retest with fragrance. For the first test, I would fill the container halfway with wax. This allows you to see how the candle will burn as the container insulates it further down.

Most containers, like glass and metal, will create more heat as the candle continues to burn further down, so we want to take that insulation into account. For example, a 3” candle may take 4 hours to reach a full melt pool the first couple of burns, and then only 2.5-3 hours at the halfway mark. The key is to find the wick that reaches a full melt pool within 4 hours on the first burn but doesn’t become a raging inferno halfway down. 

Conducting a wick sizing test

Here's how to get accurate results:

• Use a consistent container
• Sample 1-3 wicks from each brand you’d like to test
• Pour from the same batch of wax if possible, filling each container half full
• Allow the wax to cure for 1-2 days before lighting
• Burn the candles at the same time, but spaced at least 3” apart on a level surface and away from any windows or drafts.
• Set a timer (estimate 1 hour of burn time for each 1” in diameter)

The candles that reach a full melt pool (melted edge to edge and ¼” deep) will show you the potential range of usable wick sizes for that vessel and wax type. You may find that 2 wick sizes of the same brand work during this test - this is not uncommon and means you’ll want to test both with fragrance in the next round.

If you’re undecided on wax type, you’ll need to repeat this wick test with any wax or blend variation to find the best wick for each. Once you proceed to the next test, I recommend using the same fragrance oil and usage across all wax types for comparison.

Conducting a burn test with fragrance

Prep

• If possible, pour all your test candles using the same batch of wax to eliminate any variation.
• Label your candle or use a sharpie to write on the bottom. You want to note the following:
  • Wax type/blend ratio (if applicable)
  • Percentage of fragrance used (I always test at 6%)
  • Wick size and brand
• Allow your candle to cure for 3-5 days before the test burn.

Burn

• If you’re testing multiple scents, I recommend spreading them out to different spaces in your home. 
• Light your test candle away from windows or drafts and make sure they are burning on a level heat-resistant surface. 
• Set a timer (remember, 1 hour per 1” in diameter). For the Bramble Berry test, I burned each for 2.5 hours.
• If the candle reaches a full melt pool during that time, move onto the next steps.

Evaluating the results 

• Hot throw: Did the candle smell true to the fragrance while burning, and did that scent extend out into the space? For an 8 ounce candle, expect to fill 8-10 square feet. For a 2-4 ounce candle, expect to smell your fragrance within 2-3 feet. (This is an approximation). If the intensity of the fragrance isn’t very strong, consider retesting at a higher usage rate or with a different wick size. 
• Wick condition: How does your wick look after your burn? Do you see a lot of carbon buildup, which often looks like rounded mushroom tops? This is usually a sign of an oversized wick and means you should try testing down one wick size. If the wick is experiencing a lot of carbon buildup, it means your candle will burn very quickly and may get too hot, which can lead to safety issues.
• Discoloration: After your test burn, allow your candle to cool and evaluate the color. Even if you’re not using dyes, it’s important to make sure you aren’t seeing severe discoloration where the melt pool was. If dark discoloration occurs, this could also be a sign that the wick is too large, and the melt pool is overheating. Some fragrances with a high amount of vanillin may discolor a little bit, but should not be severe.

One note - if you’re using soy wax, you’ll often see bumpy and uneven tops once the candle has cooled. This is normal, and not an indicator of any variable that needs to be changed. 

Testing fragrance compatibility

Once you’ve found the wick size that works most consistently with your desired wax blend and container, you still want to test every fragrance you plan to use! If your original baseline burn test was successful with more than one wick size in your chosen brand/wick type, then test both with your fragrance to determine what works best. Fragrance oil will change the viscosity of your candle, so one wick size may end up not working in this test, or one may work significantly better.

Always test at the lower end of a usage rate so you don't waste fragrance. In my experience, if you’ve done your baseline test properly, any fragrance worth using should produce a good hot throw at 6-8%. More is not always better, and in fact some fragrances can clog the wick if too much is used.

Heavier fragrances (high flashpoint) or those containing vanillin often need a larger wick to draw the fragrance up, as does soy wax. If you’re not getting good hot throw, I find it’s often due to the wick size rather than usage rate.

Some fragrances simply won’t perform well in candles, particularly in waxes with a high melting point. Many essential oils, citrus oils, and herbal oils can produce an off-putting diesel or camphor-type smell when burned. Some menthol and camphor oils can be toxic when burned, or irritate small animals and people with asthma.

Image courtesy of Particle Goods

Always do your research when using these oils, as candle making may not be their intended purpose. Sometimes small amounts of these oils can be blended with denser, higher-flashpoint fragrances to help them perform better, but often it's an indication that they will not be compatible. Ideally, look for fragrance oils that have been specifically formulated for and tested in candle making.

We tested every Bramble Berry fragrance for candle compatibility and rated their hot throw. Scent preferences are personal, so your own results may vary depending on the materials used, but hopefully this gives you an idea of what to expect when working with these fragrances.

Please note that all essential oils were tested singularly, and some that were deemed non-compatible may work fine or better for you if used in smaller quantities or in a blend. We only tested these essential oils on their own. 

When to retest

Knowing when to retest usually comes down to knowing your materials and process. If you’re confident in your baseline test, you shouldn’t have to retest more than once or twice to know if a new component like a dye, fragrance, etc. is going to work.

Often times, fragrances can vary by batch, particularly if they include essential oils. It’s important to periodically test your candles to make sure they are performing consistently.

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