Easy Bath Bomb Recipe (see image of how bath bomb badder should look like in your hand when ready to use your mold)
In a bowl combine the dry ingredients (the first four listed above). Whisk to remove any clumps, arrowroot tends to be clumpy. In a small bowl stir together the wet ingredients which include the oxide color (the last four ingredients listed). Combine with the other ingredients. Slowly pour the liquid mixture in with the dry mixture, whisking as you go. If you see the mixture fizz or foam, you may be adding the liquid too quickly. Once all the wet ingredients are combined with the dry, take a small amount in your hand and squeeze it together. It should stick together fairly well in one or two big chunks. If it's still too powdery to hold together, just add a tiny bit more water and mix until it does hold together. It should feel like wet sand but on the dry side.
Then fill each half of your bath bomb mold with the mixture until it's just overflowing a little. Press together, then gently remove one side of the mold. Once you are ready to remove the other side, gently invert the bath bomb so the uncovered side is facing down, then gently remove the other half of the mold from the top. The keyword, if you haven't noticed, is gently. These can fall apart on you very easily if you're not careful. If a bath bomb does crack in half while you're removing it, you can gently press it back on top of the other half, or remove all the mixture back to the mixing bowl and start the molding process again. I had this happen to a few, so don't fret, it's easy to fix.
Once they are completely out of the mold, allow them to dry out for 8 hours or overnight. Once very dry, you can wrap them in plastic wrap and store in a dry place until you're ready to use them, or you can gift them to friends.