It started out as a recipe... At least as much of a recipe as you can have when you are not entirely sure what oils are in the used fry oil -- probably soybean, cottonseed, corn, canola, and various animal fats... From there, it became more of wing it thing to see what would happen if different things got added to it since I did not consider the first iteration as hard enough for a hand soap. It only got to about fudge type hardness initially. If I had never achieved a hard soap, it would not be a deal breaker though. Since it was just for my own use for cleaning grease and such off my hands, I could just cast it into a large open top container and rub my hand across the top of it when I needed to wash my hands. Kind of somewhere between a liquid and a bar soap, I guess...
The 2nd batch that I made with a single vegetable oil hardened up noticeably better, although since I didn't know what type of vegetable oil it was, I might not have had enough lye. Regardless, it worked and my wife seems to like the way it makes her skin feel -- she tends to have dry skin and normally ends up putting tons of lotions on after a shower.