I was thinking about this in the shower this morning so I'm glad you replied. Yes I understand that in the true definition of the term superfat or lye discount is that portion of the saponifiable oils which are left unreacted. Maybe a different term is in order. "Active fat"? "Effective superfat"?
What I'm getting at is let's say a fragrance oil or an EO blend is mixed with almond oil as a carrier. If that happens to be a fairly strong FO we would mix it in at .3 or .5%. We do not figure our recipe with that in mind. But when we add the fragrance the oil is absolutely there to have whatever impact it will. At .5% there's not much and it's likely within the margin of error for any given batch. At 2.5% it starts to become significant when we ponder why lather behaves differently.
I'm trying to get used to a new pair of contacts or I'd go looking for a particular thread where we discuss this. Basically with hot process you get to choose which oil is expressed in the superfat because the saponification is done at the end of the cook. Let's say you decide to use your mighty expensive argan oil for your superfat. You add it in the oils up front at that 2.5%. For the sake of argument let's say it saponifies to the same degree as the others. If your superfat calculation is 2.5% the superfact makeup is a mixture of all the oils you've used at the ratios you've used them.
Now, your very expensive argan oil which you intended to be your very nice superfat at 2.5% is really 2.5% of 2.5% = 0.0625% of the unreacted argan oil in your superfat. If you fully cook your soap and then add the superfat at the end, you get to choose what oil is used to moisturize your face. You really get 2.5% argan oil.
Good question.
The short answer is to not leave anything behind. The long answer is as complicated as you want to make it. Let's say you weigh everything into one bowl first before going to the crockpot. Arguably when you transfer that over, anything left is a representative mixture of your original blend so all of them are "left behind" in equal percentages.
Another way would be to weigh everything into the crockpot. My scale has a 2KG capacity at 0.1g resolution, so I can do my 1lb batches that way. If you are making 100g batches you can weigh them into a screw-top food storage container and use that in a bain marie as your cooker. I made a bunch in just that way. I used a scale with 0.01g resolution when I did those.
There's also a method by which chemists very accurately weigh small amounts into containers too large for the more sensitive scales. In his book, Dr Dunn calls this "weighing synthetically." You measure slightly more than you need in a container of a size which is suitable for your smaller scale. Let's say you need that 2.5g. You put ~5g in a small cup (the exact amount is not necessary yet), put your dispensing device (a pipette or an eye dropper) in the cup and tare it. You dispense into the large, heavy container an amount that leaves the scale saying -2.50g when you let the pipette or dropper rest back in it. Now you have exactly 2.50 grams if you were careful. At least you had the potential to weigh that much.
By the way, I was hoping someone else would say it so I wouldn't always be "that guy" but nobody did. :silent: Try crafting your soap without the clay. A lot of folks have found that clay does not add anything to a well crafted soap - and there are a lot of shavers (me included) who will not use a soap with clay in it. It's worth an experiment at least.
