I'm hoping this is the appropriate place to post this. This may be an odd question but I was hoping someone here might be able to help or maybe point me in the right direction. I am a hobbyist hand made soap maker and I enjoy doing various experiments with soap; testing different ingredients and what not. (I have a YouTube channel if you are interested: https://www.youtube.com/channel/UCmXiwZrRhCOfnHS7SnHOfDg). Recently one of my contacts wrote me and asked about calendula (pot marigold). Soap makers occasionally use botanicals in soap (either for specific qualities they are trying to produce in the soap...or simply for label appeal or because it's pretty). Because soap uses a strong base (lye) it creates a harsh base environment and most botanicals will turn brown. Calendula is an exception, it maintains it's bright yellow/orange color. The question I was asked, and was hoping someone might help with, is why does it maintain its color where others turn brown? If you don't know the answer, are you aware of another blog or forum or even a specific contact that might help? I'm glad to do additional research on my own, but I'm not sure where to start. Thanks so much for your time and guidance.
Though not related to soapmaking but rather food colouration, this seems like a good place to start: Maintaining Colour Stability. I would then attempt contacting Dr. David Lee, who wrote Nature's Palette: the Science of Plant Color. If you can't find an email address online, then someone from the US National Tropical Botanical Garden will know how to get a hold of him, as he is a former director of The Kampong.
