You get a fabulous new fragrance oil from a supplier, a swap, a friend. You try it out in a new batch of soap. No problems! Your soap comes out its normal lovely off-white color as it's poured in the mold. You cover it up and leave it to harden over night.
(Cue ominous music)
But something happens in the night. You come into the kitchen and unmold the soap. You notice that the top of the soap, that has been exposed to the air overnight, is slightly darker - just a tiny bit - than the rest of the creamy off-white soap. You think nothing of it, slice the bars, and put them on the rack to cure.
(Ominous music returns...louder)
The next day, you walk into your soap room (or wherever you have your soap curing), take one look at your soap and are stopped in your tracks - it's brown! Maybe not deep chocolate brown, but definitely brown! The next day...it's even browner...and the next...even browner!
What happened?
You've used a fragrance oil that contains vanilla. There is a chemical component in the vanilla that turns brown when it is exposed first to the lye, and then to the air. It's that simple. If you used a "vanilla" fragrance oil (Vanilla, French Vanilla, Warm Vanilla Sugar etc.), your soap will likely turn a deep chocolate brown over the course of about two weeks. However, I hear you cry, you didn't use a vanilla fragrance! You used "Mint Chocolate" or "Pumpkin Spice" or "Sandalwood"! Many many fragrance blends have a little bit of vanilla in them. It warms the blends, rounds out the base tones. It's a lovely part of the blends - if it weren't for the turning brown part. The more vanilla there is in the blend, the more brown it's going to turn. I had a sandalwood blend that turned a light beige. The Pumpkin Spice blend I used in the pics on the right didn't smell very "vanilla-like" but it had a lot of vanilla in it anyway. It was a medium brown after just two days!
The Solution?
Unfortunately, there really isn't one. For one, be sure to ask your fragrance supplier, or look on the website, for fragrance oil notes. Many suppliers will tell you if the fragrance will discolor. You can also check out the Scent Review Board or the Soap Dish Forum for comments about a particular supplier's fragrance. If there's one you just have to use that discolors, I recommend you just embrace the brown. Make a brown-themed soap. Add some cinnamon or brown oxide to make it even browner. Add a bit of red for a red and brown swirl. Add some gold mica for a bit of gold shimmer in the brown. You can also ladle out a bit of the soap before you add the fragrance oil, and do a swirl with the unscented part. You'll get a white & brown swirl.
There are "vanilla neutralizers" on the market, but I've not had very good luck with them. I think it's better just to know that you're going to have discoloration ahead of time...and plan for it.
