Let me start with a bit of personal history...
As a teen I got interested in some books about natural body products my mom had. They were the Jeanne Rose books "Herbs and Things" and "Herbal Body Book" and for those who know these tomes, you know they are a storehouse of knowledge. I "designed" an all-purpose healing ointment that I have been making for decades (in my late 50's now). Many folks I've given a jar to have told me I shouldsell this miracle. Long story short, I don't because I don't care to jump through the governmental and regulatory hoops. But I have contemplated what sort of product line I might have if I did start a business of natural products, based on this recipe. Soap was one of those product lines I considered and began looking into, even if only for my own family's uses.
During my research for the ointment, I learned that some oils are drying to the skin, and some moisturize fabulously. This info is located in the Herbal Body Book, Table of Oils, pgs 332-333. They are non-drying, semi-drying, and drying oils. These oils all have their various components, such as saturated or unsaturated, oleic acids, linolenic acids etc, and iodine numbers associated with each sort. I glossed over these numbers until my mom gave me a copy of The Soapmakers Companion, by Susan Miller Cavitch, and The Natural Soap Book, also by Susan.
Susan's books explain these numbers as SAP values, or saponification values, which really means, "Saponification is a process by which triglycerides are reacted with sodium or potassium hydroxide (lye) to produce glycerol and a fatty acid salt called "soap." The triglycerides are most often animal fats or vegetable oils. When sodium hydroxide is used, a hard soap is produced" (per google).
I'm still working my way toward making a lye-based soap as I have so many other things I keep busy with, including trawling the permies forums for more info on all things permie!! I fear that short of just doing it, I may never fully understand all the info in these soap-making books I have. But I did want to "add something" to the concept of a new forum for making soaps at home. And I think having a list of books to reference is a start.
“Peace is not absence of conflict, it is the ability to handle conflict by peaceful means.” —Ronald Reagan