Why test fragrances? Fragrances can wreak all sorts of havoc in soap making due to the many different components that make up a fragrance. Fragrances can discolour soap, can raise the temperature during the saponification process, can increase acceleration and cause seizing, just to name a few possible problems. But don’t think essential oils are any different, these issues can also arise when using particular essential oils! Here, I’ll be discussing why and how these problems are caused and how to prevent them. And as an extra bonus, I’ll post the results of the Candlescience Skin-Safe Fragrances, available from Pure Nature, that I’ve tested in the past month, to help you choose the right fragrance for your next project.
The main problem for soap makers is discolouration in soaps. The discolouration is usually caused by the ingredient vanillin, which the primary component of the vanilla bean extract, the bit that gives vanilla its unique scent. Fragrances that contain vanillin will inevitably turn to brown. How much the discolouration and how quickly a soap will turn brown, depends largely on the percentage of vanillin a fragrance contains. Fragrances with a high percentage of vanillin, 10% or more, will turn to a dark brown, whereas those with only a small amount, less than 1%, will only discolour slightly and often only after some time has passed, which is why fragrance testing takes a while. You only know the full extent of the discolouration after a soap has been completely cured. Incidentally, discolouration also affects melt and pour soap bases and other skin care products. The reason for the discolouration, as it often is, is caused by the villain oxidation. Oxidation occurs when chemicals react with the natural oxygen present in the air. You could, of course, try and wrap your soaps airtight, but that would only work for a limited time and only with melt and pour soaps and lotions. Cold and hot process soaps need to cure, which can only happen if they’re unwrapped. And curing causes discolouration…. see the dilemma?
In the above two pictures, you can see vanillin at work. The picture on the left was taken after 1 day of curing, the picture on the right after 5 days. Discolouring will continue until the whole soap has become the same colour as the edge. Vanillin discolouration is a totally natural process, and you cannot prevent it from happening. But there are chemicals that can slow this process down. They don’t completely eliminate the discolouration, but can stabilise the fragrance and postpone the discolouration for several months. Now if you’re like me, I’d like my soap to keep looking like it did when I gift or sell it, and having it turn brown in someone’s pretty soap dish after half a year seems a bit misleading to me. Nevertheless, if you would like to explore this option, the product is called Vanilla Colour Stabiliser, and it works by counteracting the oxidation of the vanillin, but as I mentioned before it won’t last for ever. The longest I have seen it working was about half a year.
The much better solution is to work with the discolouration. If you know the fragrance will turn your soap in a shade of beige, caramel or brown, use this in your design. You can leave a small portion of your soap unfragranced, which keeps parts of your soap white. For example, adding a white swirl or white layer in your otherwise brown soap. A fragrance that only discolours slightly can be ‘coloured over’ with other colours, such as oranges and reds. However, remember that some colours don’t mix well with brown shades. Green, for example, mixed with brown will result in a rather unpleasant shade. And lastly don’t forget that often those fragrances that contain high percentages of vanillin, tend to be fragrances that we naturally associate with warm, brown colours anyway: creme brûlée, chocolate, and anything vanilla or custard-like.
Check out this cool Pumpkin Spice Soap, which uses the fragrance to enhance its design.
If you absolutely do not want your soap to discolour in any way, I suggest you choose a water white fragrance – fragrances that are clear in colour, contain no vanillin, and do not cause discolouration. More about this next week!