To make bath bombs successfully, have ingredients ready to mix. Choose your moulds carefully and have, at least, 2 molds ready for filling. Read the instructions first so you know what you are doing. Carefully measure out the wet ingredients (if you have too much, you will end up with "slop", and, if that is the case, just dry the product out and leave it loose (it will still work!).
To Start: Combine the baking soda, citric acid, cornstarch, and borax.
Melt the cocoa buter in a microwave safe measuring cup or over low heat in a small pot. Add to the baking soda mixture. Combine the mixture and add the essential oils. Mix well. Mixture should hold together when you make a ball.
Working quickly, press the mixture FIRMLY into your mold, making sure the edges are clean. Leave the mixture in to the mold for a couple of minutes, then pop out. While one tray is drying, work on the other (I put a small cutting board over top of the mold, flip over, then lift the mold off). Let bombs dry overnight undisturbed. Once dried, place them in a decorative bag and tie with ribbon.
To use: Drop 1 bomb into your tub and relax.
~Or~ leave the mixture in the mixing bowl for 24 hours, periodically mixing the ingredients, breaking up the clumps. Once the product has dried out, place in a nice decorative bag with a colourful ribbon. Makes nice gifts.
Helpful Hints: Your favorite perfume could be used in the bomb. Realize that while it is messy, wasteful, and considering how expensive perfumes are -- but it can be done. Remove the sprayer nozzle and spray into a measuring cup the desired amount Because perfume is so concentrated, use 3/4 - 1 tsp, or until you are satisfied with the smell.
I have used large ice cube trays that I use just for bath bombs. When picking a mould you want something that is not too big (you end up wasting product) and soft edges (the bombs end up too fragile with sharp angles). When the bombs are in the molds, and I have pressed firmly down, I will run a sharp knife along the bottom of the mold to get a clean, flat edge. You can put lavender flowers, rose petals, etc in your mixture, but sometimes it ends up clogging your drains, so think carefully about what you are putting in the bombs -- if you put too much dried fowers in the bomb may not come together.
Commercial bombs have lots of hidden ingredients it them that are not necessarly good for the skin, like Sodium Laurel Sulphite -- which gives you the "bubbling action" You get nice bubbles, but this product (in its raw state) will actually burn the skin.