Oil-in-water and water-in-oil?
The type of emulsion you make isn’t just about how much oil or water we have in a lotion – like, more water = oil-in-water (o/w) or more oil = water-in-oil (w/o) – but about the emulsifier. This emulsifier creates oil-in-water lotions, those in which the oil is encapsulated in micelles floating in a sea of water, not water-in-oil lotions, those in which the water is encapsulated in micelles floating in a sea of oils.
Emulsions have an internal phase or dispersed phase – those things that are inside the bubbles or micelles – and an external phase or continuous phase – those things that are outside the micelles.
The type of emulsion we have is about what’s inside and outside, not necessarily quantity of water or oil in the formula. We need to use very specific emulsifiers and methods to make each type, and we can’t just make a water-in-oil emulsion by having more oil than water in a formula with an emulsifier like Polawax because it makes o/w lotions, not w/o lotions.
Read more in this post about Bancroft’s rule and emulsifiers!