To make lye soap from scratch, you’ll need lye, water, and fats or oils such as coconut oil, lard, or olive oil. First, mix the lye and water in a non-reactive container, preferably a heat-resistant glass or ceramic one. Once the lye has dissolved, heat the fat or oil in a separate pot until it melts. Then, slowly pour the lye solution into the melted fat, stirring constantly. The mixture will begin to thicken and eventually reach “trace,” a point where the soap mixture can hold its shape. Once it has reached trace, pour it into soap molds and let it sit for a day or two before cutting it into bars. Let the bars cure for several weeks before using them.