Cure Times for Fragrance Oils in Wax Melts and Candles

Posted by andrew sanderson on

There is lots of talk about cure times and the fragrances from fragrance oils becoming stronger, the longer the wax cures.

We have done a lot of research into this and here are our findings. The pro-cure people may want to look away at this point.

The argument for curing is that the wax and fragrance oil need time to cure which makes the oil bond with the wax. Different waxes are said to need more or less time to cure.

For curing to take place and for the fragrance oil to bond with the wax, every fragrance oil would have to be chemically the same to allow the oil and wax to chemically bond in the same manner. As different fragrance oils have different chemicals and essential oils (in many cases), all oils are chemically different and so for the fragrance oil to bond the wax the same bond could not occur with every oil in the same wax.

There is no reaction happening, no bonding or binding happening in the curing of wax and fragrance oil, not in the chemical sense of the word. This would involve the donation or sharing of electrons in the outer shell of the atom or molecule, an interaction, force or attraction of some type between atoms, molecules or compounds. The mixing of fragrance oil and wax is more accurately described as the mixing of two fully miscible liquids to produce one homogenous liquid. This means the molecules will mix with each other to form a uniform liquid. On cooling the fragrance oil and wax molecules will be ‘trapped’ ie fit together rather than actually chemically bonding or binding. There will be some minor settlement between the molecules but nothing that will significantly affect the fragrance in the finished wax. It is important that the fragrance oil is added to the wax at the correct temperature otherwise the fragrance oil can sweat out of the solidified wax. When making fragranced candles the wax needs to be left to ‘cure’ a day or two to allow the wax to fully solidify (see the technical data sheet for each candle or wax melt wax). A candle is much more complex than a wax melt due to the way that the fragrance is released.

Fragrance is released from a wax melt or candle due to the wax/oil mix being heated. The throw is different between the two due to the way that the oil is released (via the wick or via the melt). However, the principle is the same. The top, mid and base notes are released due to the melt of candle being warmed, giving the fragrance oil molecules the energy to free themselves from the wax. You smell the base notes later than the top notes as the base notes need more energy to free themselves as they are bigger molecules. If the wax and fragrance oil bonded, the reason for argument to cure, the fragrance oil would not be released and would remain chemically bonded to the wax, giving no fragrance as they would chemically be one. You can however put too much fragrance oil in a candle which will give cold throw but no hot throw. This is because no fragrance oil is getting drawn up the wick, the wick can be blocked by too much oil.

The fragrance oil that you put into a melt or candle has the ‘strength’ of fragrance that the perfumiers design the oil to have. By curing, there is no magic reaction which amplifies the fragrance. If this was the case, the chemical reaction would be different for every fragrance chemical and some notes would be ‘amplified’ more than others, giving a fragrance blend that is out of balance with the intended fragrance oil.

We have tested our wax melts at one day and 2 weeks+ and the throw is the same. We asked our fragrance oil manufacturer and a wax supplier what time is needed for curing and they both gave the same answer – around 48 hours for the wax to fully set and the molecules to settle. This is also reflected in the wax manufacturers Technical Data Sheet.

We suspect that curing is part of the mystique transferred from cold press soap where the soap does need to cure. In soap curing the water evaporates and the soap hardens. This is to firm up the soap and to help the soap to last longer. The fragrance can be affected by the saponification process. This does change the fragrance as when the water is reduced, the fragrance becomes more concentrated. As there is no water in wax, this does not happen in wax melts and candles.

Our advice – if curing makes you happy, stick with it. If you cant tell a difference, ignore it.

Link to an example of a technical data sheet (Kerax 4600)


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