Safety is important when making soap. Be sure to wear gloves, goggles, and long sleeves. Work in a well-ventilated area. Get someone to watch your kids or pets while you work - you should not be disturbed while making soap.
Place coconut oil in a medium stainless steel pot over low heat. Stir until fully melted. Remove from heat.
In a well-ventilated area, and with gloves and goggles, slowly add lye to water, stirring until fully dissolved. Let it cool.
Allow both the oil and lye solution to cool to 37–43°C (100–110°F). They don’t need to match exactly.
Once cooled, slowly stir the lye solution into the melted oil. The mixture will turn creamy and opaque.
Use a stick blender in short bursts, alternating with stirring, until the soap thickens to light trace (thin ribbons remain briefly on the surface). Blend in essential oils if using.
Place silicone molds on a sturdy tray. Ladle soap into molds, leaving a little space at the top.
Cover molds with plastic or baking paper, then wrap with a towel or blanket. Let rest 24 hours.
Wash all tools immediately with hot, soapy water by hand.
After 24 hours have passed, check your soap. Wooden/cardboard molds: cut when firm. Silicone molds: may take several days to remove.
Place bars on a rack in a dry, cool area with good airflow. Cure 4–6 weeks.