With this amount of dry goods I would add about 2 tbsp of liquid (any combination of oils, melted cocoa or shea butter and even some water or witch hazel).

Sift all your dry ingredients together and add the salt if using. (The salt adds a bit of "shine" to the ball and helps soften the water).

Slowly drizzle some of the liquid into the dry mixture while continuously moving the dry goods around with your hand (a rubber glove is recommended). Add more liquid at intervals mixing well in between each addition. Once the mixture is "formable", press into the two halves of your Bath Bomb mold; Then press the two halves together being careful not to twist them together.

Let sit for a few minutes and then unmold. Let them air dry overnight. If the ball sticks to the mold and comes apart you may be able to rescue it by adding some more dry ingredients to the mix.