Safety First! Remember to wear your safety equipment and mix the lye water outside.Tell everyone you live with that where you're working is off limits. `Give yourself enough time to complete the recipe.
Prep Ahead: Combine water and kombucha and chill in the refrigerator.
Heat the Fats/Oils: In a large pot over medium-low heat, combine tallow, coconut oil, olive oil, argan oil, and mango butter. Heat until they are melted and incorporated. Remove from heat and allow to cool to 100-110°F.
Mix the Lye-Water: Put on protective gear including a mask, gloves, and long sleeves. Outside, carefully add the lye crystals to the kombucha water and stir until dissolved. Allow to cool to 100-110°F. If oil or lye water cool at different, you can use a cold or hot water bath in the sink.
Prepare the Mold: While the oils and lye water cool, line the mold with parchment paper.
Combine and Bring to Trace: When both oils and lye water are around 100 to 110°F, pour the lye water into the pot of oils. Use a stick blender or hand mixer to mix for 1 to 2 minutes and then let the mixture rest for 4 to 5 minutes. Repeat mixing and resting until light trace.
Mold the Soap: Pour the soap mixture into the mold, cover with a lid or parchment paper and insulate with a blanket for 24 hours.
Cut and Cure: Remove soap from the mold. If it seems too soft to remove, wait another 12 to 24 hours before removing. Cut the soap into twelve 4-ounce bars. Allow the bars to cure for 4 to 6 weeks.