Welcome in the wonderfully scented world of fragrance oils!
These synthetic oils are probably the best and less expensive way to add scent to your candles. Furthermore, they will tempt you with an almost endless choice of available scents.
But there are several things you must know before you start using fragrance oils in your homemade candles.
By its chemical composition, paraffin is very close to oil. Just as it happens with oil, if you were to pour water in your double-boiler insert full of melted paraffin, water would head directly towards the bottom of the pan with paraffin floating on it (another reason why it would be excessively stupid to try and put off an oil fire - or a paraffin fire - with water).
Experience will show you that, whenever you see some kind of big bubble rolling underneath your melted wax, it's a drop of water that felt into your paraffin.
You've got it by now: it would be useless to try and use a water-based or alcohol-based perfume in a paraffin wax. Birds of a feather flock together: the only solution is to use oil-based scents.
If you happen to visit websites that sell handmade candles, you will often hear expressions like "triple scented candles".
This means that the candlemaker used three times the industry standard. This standard is 0.5 ounce (21.3 grams) of fragrance oil per pound (450 grams) of paraffin wax.
So in our example of the "triple scented candles", 1.5 ounces (42.5 grams) of fragrance oil were used for every pound (450 grams) of paraffin wax.
That's a lot and it's about the most paraffin can take (3% volume of oil is considered a maximum).
If you use more than 3% oil, your candle could be covered in "snowflakes" (this is also called mottling) under its surface.
As a matter of fact, as this "mottled" effect can be quite pretty, it is often achieved on purpose. If giving your candles a mottled effect is your intention, you should probably use mineral oil instead. It is commonly available and a lot less expensive than your precious fragrance oils.
Be aware that using too much oil will result in a "sweating" or "bleeding" candle, with oil coming out from everywhere! It this happens, don't sweat it: wipe your candle regularly with kitchen paper during a few days until the excess oil is gone. When the bleeding has stopped, your candle should still be okay to burn.
Every oil has a flash point (or ignition point), FP in short. That's the temperature at which it may catch fire. The same applies to synthetic oils.
To complicate matters, a synthetic fragrance oil often contains more than 50 different chemical substances, each one having an influence on the general flash point of the compound. As a result, fragrance oils all have a different flash point, and that has the potential to create some headaches...
Some big differences there.
So what happens if you add a fragrance oil with a 130°F flash point to your paraffin wax currently heated to 180°F?
Nothing. It won't start a fire because the amount of fragrance oil is minimal compared to the amount of paraffin and because the flash point of that same paraffin is much higher.
HOWEVER: your fragrance oil is considered "burned". In other words, its chemical components (along with its scent) are damaged. In most cases, this just means the scent will be non-existant but if you're out of luck, it might just as well reek like a dead rat.
You can see where I'm headed: it is essential to know the flash point of each and every fragrance oil you will be using.
In theory, that piece of information should be found on the label, but it's rarely the case. You should also be able to obtain it from your supplier, even more so if you purchase your fragrance oils online. And ideally, this information must be available PRIOR to purchase.
Be aware that the supplier MUST be able to give you safety informations upon simple request. If he doesn't, simply stop buying there and let him know why. It is not only a lack of professionalism but also a safety hazard.
(Material) Safety Data Sheets, or (M)SDS, are key documents in the safe supply, handling and use of chemicals. They should help to ensure that those who use chemicals in the workplace do so safely without risk of harm to users or the environment.
Every fragrance oil should be documented on its own Safety Data Sheet, created by the manufacturer.
For an example of a Material Safety Data Sheet, click on the Pdf icon.
The one in this example refers to a strawberry scented fragrance oil. As you can see, there's a lot of verbose but I highlighted two important informations: "Solubility in Water : Insoluble" (of course: it's an oil) and "Flash Point : ~150°F". That's what you need to know right there!