Wicking Eugenol Candles: Soot, Tunneling and a Test Method
There is no spice-oil wick rule. We found no source that says eugenol, or a clove-type blend, needs a bigger or smaller wick than any other fragrance, and we publish no wick grids of our own. What does exist is a method: change one thing at a time, burn each candle in cycles, write down six readings and let the symptoms tell you which way to move. This guide is that method, with the sourced numbers and the reasoning behind each step.
Start from the symptom, not from the oil
The wick guidance we read from Supplies for Candles, a UK candle supplier, gives these moves. Treat it as one supplier's guide, not a standard.
| What you see | Likely direction | Then check |
|---|---|---|
| Tunnelling, or no full melt pool by hour 3 to 4 | Wick up one size | Does the pool reach the container edge in the stated time? |
| Heavy mushrooming, soot on the vessel, very tall flame | Wick down one size | Flame height; the guide calls about 10 to 15 mm stable and moderate |
| Melt pool too deep, or vessel uncomfortably hot to hold | Wick down | Container temperature at the end of each burn |
| Wick that burned well in unscented wax now struggles | Suspect the fragrance load or an oil that clogs | Repeat the series with the new load |
Why fragrance load shifts the answer
The same supplier guide says higher loads often need a bigger wick, lower loads can raise burn rate, and "even a 1 to 2% change can impact performance." It also says "heavy vanillin or resinous oils can clog a wick" and that some essential oils burn hotter. Eugenol is not named in it, so whether our material belongs in the clogging group is unknown. Reasoning from the fuel picture: the wick draws liquid wax up by capillary action, and anything dissolved in that wax changes its viscosity and what reaches the flame. An oil that is heavy, high-boiling or reactive might change how well that works. That is a mechanism to test, not a finding.
Here is the sensitivity as arithmetic. Suppose you pour 300 g of wax at an 8% total load: 300 x 0.08 = 24 g of fragrance. If eugenol is 10% of that blend, it contributes 2.4 g, or 0.8% of the wax weight. Move eugenol to 20% of the blend at the same total load and it contributes 4.8 g, or 1.6%. The total load did not move, but the share of one material doubled. Against a supplier statement that a 1 to 2% change in load matters, a swap in blend composition is reason enough to re-run the wick series. The numbers are illustrative, not a recommended recipe, and we have not tested any blend.
The wick series, step by step
This is the procedure from the Supplies for Candles guide, with the two points that matter most for a spiced blend.
- Pick three wicks. Your estimated size, one size down and one size up.
- Hold everything else constant. Same wax batch, same fragrance percentage, same vessel, same pour temperature. Only the wick changes.
- Label and rest. Container size, wick, pour date, fragrance and load. The guide says not to rush this. Its rest times vary by wax: paraffin 24 to 48 hours, some soy blends 10 to 14 days, a coconut blend 7 to 10 days. IGI 6046 notes at least three days. Use the wax maker's figure.
- Burn in 4-hour cycles with a full cool-down between. Continue through the candle's life, not just the first burn.
- Record six things after each burn: melt pool diameter, flame height, mushrooming, sooting, container temperature, time to full melt pool.
- Pick the wick that reaches a full melt pool by hour 3 to 4 without soot or a hot vessel. If two qualify, take the smaller.
For starting points, a supplier's lab notes on IGI 6046 say that for a 3 inch (7.6 cm) container the largest or next-largest wick in most series did best, containers over 3.25 inches may need double wicking, and one wick series mushroomed even when sized properly, so trim between burns (CandleScience). That was one wax and unrelated fragrances. It tells you the order of magnitude of testing, not what to buy.
What soot studies say about wicks and waxes
Two papers help set expectations, neither involving eugenol. In a 2021 chamber study of five pillar candles with different waxes and wicks, the authors reported that "the wax and wick composition strongly influenced emissions of BC [black carbon], PM2.5, and particle-phase PAHs", and that short-lived strong peaks of soot appeared directly above the flame under "stressed burning" with fluctuating air velocities (Andersen et al., Indoor Air, 2021). Their point is that the entire burn matters, and that preventing stressed burning can lower exposure. The practical consequence, reasoning from that design: run your wick tests in still air, then run one more burn in a mild draught and see how the flame behaves.
A separate study of 24 chamber runs combined four waxes and five fragrances (Salthammer et al., Environment International, 2021). It reported that the exposure scenarios calculated from the emission rates were mostly well below indoor guidance values, with exceptions for nitrogen dioxide, acrolein and benzo[a]pyrene in some cases. The abstract does not say which fragrance ingredients drove which result, and eugenol is not named. We cannot tell you from either paper that a spiced blend sooted more than a floral one.
Wax changes the answer too
A wick sized for paraffin is not a wick sized for soy. A 2002 study of hydrogenated soybean oil candles reported that paraffin candles gave off "a considerable amount of soot" while soywax candles gave little or none, and that soywax candles burned more slowly (Rezaei, Wang and Johnson, J Am Oil Chem Soc, 2002). Burn rate differences are why one wick series cannot be carried across waxes. Our wax comparison sets up the side-by-side; run the wick series inside each wax separately.
Unattended burning and who to ask
A wick test means burning candles for hours. ASTM F2417's scope page says the candle specification does not replace "adult supervision, close monitoring, fire detection, alarm or suppression systems, and use of candles away from combustible materials" (ASTM F2417-24). Do not leave test candles burning unattended, put them on a non-combustible surface and keep a means of putting out a fire nearby. See our flash point guide for the wax-pot side. If you sell candles, how you test, label and document them is a question for a product-safety specialist or attorney. We sell eugenol oil only; wicks, waxes and containers come from candle suppliers, who can usually give you a starting wick chart for their wax.
What this guide does not claim
It does not say a particular wick works for eugenol blends, that eugenol soots, or that it clogs. We have no burn data. It also does not claim that every spiced candle needs a larger wick. Our spiced candle post deals with loads and rest times, and the wax melts guide covers the flame-free format where wicking is not an issue.
Our eugenol oil is sold undiluted, so every percentage above is arithmetic you do on your own scale. Weigh it, write it down and let the burn log, not a rule of thumb, pick the wick.
Sources & Further Reading
- Supplies for Candles. The complete guide to wick testing. suppliesforcandles.co.uk
- Andersen C et al., 2021. Emissions of soot, PAHs, ultrafine particles, NOx and other health relevant compounds from stressed burning of candles in indoor air. Indoor Air. pubmed.ncbi.nlm.nih.gov/34297865
- Salthammer T et al., 2021. Measurement and evaluation of gaseous and particulate emissions from burning scented and unscented candles. Environ Int. pubmed.ncbi.nlm.nih.gov/33964641
- Rezaei K, Wang T, Johnson LA, 2002. Combustion characteristics of candles made from hydrogenated soybean oil. J Am Oil Chem Soc. europepmc.org/AGR/IND500743523
- CandleScience. Lab notes: IGI 6046 coconut paraffin candle wax blend. candlescience.com/learning
- ASTM International. F2417-24, Standard Specification for Fire Safety for Candles (scope page). store.astm.org/f2417-24