I should have mentioned,I’m making liquid soap. It’s the neutralization process and checking for excess lye.
As far as using glycerin in soap.. I use it all the time when making my liquid deturgent/dish soap. I add it in with the lye water, after the lye and water is completely mixed and clear.
I know about the Zap method but have never used it. I've used Phenolphthalein to test for excess lye for the past year of liquid soap making. Taking a small amount of soap and mixing with boiled and hot distilled H20, cooling it, and then testing with a few drops of Phenolphthalein. If it's pink...