Castor oil will speed up the rate at which your soap will get to trace - so we usually leave it out of recipes that require complex swirls or designs. All of the soap recipes in Sandy Maine’s book, “The Soap Book” are made with 44% vegetable shortening (Crisco), 28% coconut and 28% olive oil. If it’s good enough for Sandy Maine (of SunFeather Natural Soap Company), it must be pretty good. (Note: Her book was published before the controversy over cottonseed oil arose, though. (See above.) She may have reconsidered.)