I am outlining a class I'm going to teach on HLB theory. There seem to be a million sources on the internet to explain how to calculate the HLB of a (nonionic) surfactant in order to match it to the "HLB" (or more correctly the "required HLB) of the oil that is going to be emulsified. However, I am having great difficulty finding an explanation of how the required HLB of an OIL is determined in the first place. I can find lists of the required HLB of various commercially important oils but not how they were determined! Was it just trial and error? Was it the inverse case - the HLB of the surfactant that successfully emulsified the oil was known so that HLB was assigned to the oil? This would seem to be a fundamental principle in this area of surfactant science but I'll be darned if I can find the information. Anyone have an explanation or an example of a method for determining the required HLB of an oil?