Add the cetyl alcohol, coconut oil and cocoa butter to a double boiler over medium heat, stirring frequently until all ingredients are completely melted. Once melted, add the melt and pour soap cubes and continue stirring frequently until the mixture is melted and smooth. (If you don't have a double boiler, you can fit a glass bowl into a pan of water.)
Stir the apple cider vinegar, sea salt, baking soda, Vitamin E and Argan oil into the mixture in the double boiler.
Add the essential oils and soap colorant and stir to until well combined.
Stir in the crushed lavender, reserving about 2 tablespoons (optional).
Sprinkle a bit of crushed lavender into each cavity of the soap mold (optional).
Gently pour the shampoo bars mixture into your silicone mold.
Spray the top of the mold with a spritz of rubbing alcohol to dissipate any bubbles.
Allow your homemade shampoo bars to harden at room temperature or in the refrigerator for at least two hours until completely cool. Store the shampoo bars in an airtight glass container until you're ready to use them.
How To Use Shampoo Bars
Lather up the lotion bar in your hands, then wash your hair as usual.