Okay. What exactly is "sugar syrup"? Is this something you buy already made? Or is this something you make by adding sugar to water?
It's also called simple syrup. You make it yourself exactly as you said.
edit: You don't need to use sugar syrup to make soap -- just dissolve the sugar in water or water-based liquid. Make sure the sugar is fully dissolved before adding the lye. Then there's no need to worry about the water added by using sugar syrup.
But this is purely a preference thing -- the soap maker gets to choose which works best for them.
I'm adding the syrup as a percentage of total batch weight. Maybe I should change it to percentage of oil weight?
The basis (fat weight vs batch weight) isn't super critical, as long as you use one or the other consistently. See below for why people usually use fat weight for soap making, however, rather than batch weight.
I really wanted to know if you're using a percentage to get the weight of syrup or if you're adding an absolute weight so I could give you an intelligent answer. Many soap makers struggle with math, and avoid percentages like the plague, so I never assume how "mathy" a person is.
Most soap makers who are comfortable using percentages will use the fat weight as the basis, rather than total batch weight.
Batch weight changes as soap cures and loses water due to evaporation. It also changes from recipe to recipe if you change the lye concentration or add/subtract other additives. Fat weight remains constant. So if you want a consistent basis, fat weight is a better choice versus batch weight.
It's like using bakers percentages" when working with a bread recipe -- the amount of water and salt and yeast are based on the flour weight, not on the total weight.
