Most “mysterious” candle problems are not caused by the wax or fragrance: they are often related to wick selection.
Choosing the right wick means choosing the right combustion engine. If it is undersized, you may get tunnelling and a small melt pool. If it is oversized, you may get an excessively high flame, soot and excessive consumption.
This guide provides a practical method for choosing candle wicks using technical criteria, whether you make candles as a hobby or produce them to sell.
What does a wick actually control?
A suitable candle wick should:
- Feed a stable melt pool.
- Maintain a consistent flame without excessive smoke.
- Burn safely and predictably.
The wick carries fuel — liquid wax — towards the flame. This means anything that changes the viscosity or hardness of the system, such as wax type, additives or fragrance, can change the wick choice.
Which variables change wick sizing?
1. Usable diameter of the container or candle
- For a container, use the internal diameter as your reference.
- For a mould, consider the maximum diameter or width of the candle.
2. Wax type
Soy, paraffin and vegetable blends behave differently. Some waxes require a wick with greater fuel-delivery capacity, while others work better with a more moderate option.
3. Fragrance load and fragrance type
Fragrance changes the combustion system. Two identical candles with different fragrances may require wick adjustments.
4. Colourants and additives
Colourants and additives can also alter combustion. If you change the formula, validate the wick again.
5. Candle type
- Container candle: look for a controlled melt pool, stable flame and reasonable consumption.
- Moulded candle: look for an even burn compatible with the shape and hardness of the wax.
How to choose the wick step by step
Step 1. Define the complete candle system
Record:
- Candle type: container or mould.
- Diameter.
- Base wax.
- Fragrance percentage.
- Use of colourant or additives.
- Burn-test objective.
Step 2. Choose several candidate wicks
Work with three sizes around the initial estimate: one slightly smaller, one central and one slightly larger. This lets you compare results without changing other variables.
Step 3. Test under comparable conditions
- Same room.
- No draughts.
- Same curing time.
- Same initial wick-trim height.
Step 4. Evaluate how the burn develops
Do not judge only the final result. Observe different stages of the test and record:
- Size and development of the melt pool.
- Flame height and stability.
- Presence of smoke or soot.
- Mushrooming on the wick.
- Persistent tunnelling or overheating.
What does a good melt pool mean?
In a container candle, the goal is not to achieve a full melt pool as quickly as possible if that creates an excessive flame or soot. Look for progressive development, a stable flame, little smoke and reasonable consumption.
How to correct typical wick problems
Problem 1. Tunnelling or a melt pool that is too small
Common causes:
- Wick too small.
- Harder or more viscous wax.
- Diameter too large for that wick.
What to try:
- Move up one wick size.
- Check the actual container diameter.
- Revalidate the wax, fragrance and wick combination.
Problem 2. Soot or blackened walls
Common causes:
- Wick too large.
- Flame too high.
- Excess fuel in the melt pool.
What to try:
- Move down one wick size.
- Review trim height.
- Check whether the formula needs a different wick family.
Problem 3. Unstable flame
Common causes:
- Draughts.
- Wick not well suited to the formula.
- Insufficiently homogenised mixture.
What to try:
- Control the test environment.
- Improve homogenisation.
- Try another wick size or type where appropriate.
Problem 4. The candle goes out by itself
Common causes:
- Wick too small.
- Formula too heavily loaded for that wick.
- Insufficient melt pool.
What to try:
- Move up one wick size.
- Review fragrance load and compatibility with the wax.
Burn-test template
- Diameter: ___
- Wax: ___
- Fragrance (%): ___
- Wick: ___
- Curing time: ___
- Result: melt pool, flame, smoke, walls, stability and consumption.
Common wick-testing mistakes
- Using different containers in the same comparison.
- Changing several variables at once, for example wick, fragrance and wax.
- Not documenting results, which prevents consistent batch repetition.
- Trying to achieve a full melt pool too quickly, even when the flame becomes excessive.
Frequently asked questions about candle wicks
How do I know if the wick is too small?
If there is persistent tunnelling, a small melt pool and a weak flame, the wick may be undersized.
How do I know if the wick is too large?
If there is soot, a very high flame or excessive consumption, the wick may be oversized.
Can fragrance change the wick I need?
Yes. Different fragrances and percentages can alter combustion and require adjustments.
Can you choose a wick without testing?
Not reliably. A chart or initial recommendation helps narrow the options, but the burn test confirms the choice.
Which matters more: wax or diameter?
Both are important. Diameter determines the power required, while wax, fragrance and additives fine-tune the system behaviour.
For consistent results, choose the wick methodically: diameter + formula + burn test.
