Excerpt:
In Colonial times, soap was made primarily from pork fat and a crude form of lye. The lye was tested for suitability by dropping an egg into it. If the egg floated, the lye was too strong. If it sank, the lye was too weak. It had to suspend or sink very slowly to be right. This doesn't quite compare to the computer generated formulas of today. However, it was the pork fat base (not the lye) that made this soap good for washing clothes, but often harsh to the skin