Combine all dry ingredients (except color) in a bowl. Whisk until evenly mixed.
Combine all wet ingredients (except color) in a small glass vessel (a shot glass works perfectly).
Very slowly, stir the liquid mixture into the dry mixture, whisking as you go. If you see lots of fizzing, you’re going too fast. If you’re using food drops for coloring, add them now.
After all ingredients are evenly combined, the mixture should feel like damp sand. To test it out, put a small amount in your hand and squeeze. It should stick together in 1–2 big chunks once you release your hand. Add a few more drops of water if it doesn’t. Once you reach the desired consistency, mix in the color powder (if using).
Fill each half of your mold with the mixture until it is a little over-filled, but don’t pack too densely. Loosely sprinkle some more of the mixture on each half (this helps the two sides meld).
Press the halves together firmly and hold for a few seconds. Gently remove one side of the mold.
Place the bath bomb mold side down and allow to dry for about 20 minutes. Carefully remove the other side of the mold in a gentle twisting motion. (Pro tip: Bath bombs can fall apart very easily, but you can remold one side or re-mix the whole ball and start over if you need to.)
Let sit for a few hours (or preferably overnight) until bath bomb is totally firm, then enjoy a soothing cannabis-infused bath and let your stress melt away!