It got so hot the lye melted a hole in the bottom of the plastic and ran all over the place. Ice water will also help prevent this from happening. I like using lye like this because the chemical reaction between the lye and carbon dioxide in the air forming sodium carbonate won't go into suspension in the water. It settles out in the bottom of the container, keeping it out of my soap. Soap made from lye, or sodium hydroxide, makes solid soap.
Potassium hydroxide makes liquid soap.
When adding the lye water to the melted fats, stir the mix in only one direction as you pour in the lye water. Pour it slowly so the water stream is no larger than the diameter of a pencil. Stirring in one direction only spins out the lye stream into a very thin thread. Adding the lye water in this way should should prevent it from settling out in the bottom of the pot. After you've added the water, quickly stir the mix in a figure 8 motion.