Combine the lye and water. In separate, non-reactive containers, measure out the lye and water. Add the lye to the water, stirring until the lye dissolves. Set aside in a safe, well-ventilated place and allow the lye water to cool to 100-115 degrees while you melt the oils.
Melt the oils. Add all the oils and butter to a large, non-reactive saucepan and melt over medium-low heat until fully melted. Set aside to cool to 100-115 degrees. This may take an additional hour or so.
Combine lye solution with the oils. (Before blending, prepare your soap mold and have your oatmeal, fragrance, and colors ready to go.) Pour the lye water into the pot with melted oils and combine with a stick blender until “trace” is reached. The batter has traced when a trail rests on the surface of the liquid rather than immediately sinking back it. Add the oats, fragrance, color, and stir by hand.
Pour soap into mold. Immediately pour into the soap mold. Allow the soap to cure in the mold for 24 hours. To prevent gel phase, put it in a cold place such as the fridge. To force gel phase, place it in a warm (140 degree) oven, then turn the heat off and allow to finish curing in the oven.
Unmold and cut into bars. Carefully turn the soap out of the mold. Cut into bars. Place on breathable fabric or wire racks and allow the soap to finish curing at room temperature in a well-ventilated space for at least two weeks. A longer cure time will result in harder, longer-lasting bars.