Step 5: Unmold and let dry
You can use all sorts of things to make your bombs; muffin tins, ice cube trays, candy molds, Aunt Magnolia's denture case . . . whatever makes you happy.
This batch didn't make quite enough for five bombs, and the humidity levels made the batch start to puff up, so I quickly stuffed what was left of the batch into my "bath cookies" mold. Note: When using things like silicon trays that surround the seltzer mix, or any mold with a lot of details, the mix must stay in the mold until dry, or it will crumble when you try to take it out.
Once they are completely dry, store bath bombs in an airtight container or bag. High humidity will make them activate. Because we used oil and water and no preservatives, you want to use them within about 6 months. Assuming you can keep them for that long. Igor demands payment in immediate fizzy baths, but you may have better luck actually getting to *use* yours.
When you're ready to use one, just drop it into a warm bath, and relax.