Wondering how soap-making scales down: Is there a limit to the smallest batch size? I guess the chemistry is the same, but are there practical limits? E.g. I want to make one or two bars (instead of ten bars) for my first attempt.
Stashgrower, most of the "1 batch" recipes I've seen make 1 loaf pan's worth, which really isn't very much, although still ten bars rather than 1-2. :) You could scale down the ingredients to a point. I think the smallest ingredient is the lye, which in our recipe is still a couple of tablespoons, iirc, so you could go down a bit. You would need a mold to fit a smaller recipe, but maybe a silicone muffin tray would let you make a few smaller bars?
That said, I'm not sure there's any advantage to scaling down. The recipes are really straightforward, and although you can make really nice or less nice soaps, there's not really a way you end up with an unusable product if you're following the instructions, even if you don't know what you're doing. If you were worried about wasting ingredients and wanted to do a test batch, I would just start with a super-simple recipe and get the hang of the process.
The only thing we've ever had go wrong was that the smells fade or we don't like a particular additive (like oatmeal or orange zest or something scratchy). But we still used the soap up; it was still soap. :-)