- Time: 10 minutes of work, several hours of drying time
- Cost: About $2 per bomb if you make a dozen and more if you add biodegradable glitter—but prices drop if you make a big batch
- Difficulty: Easy
- 8 oz baking soda
- 4 oz Epsom salt
- 4 oz corn starch
- 4 oz citric acid
- Large bowl
- Biodegradable glitter or dried flower petals (optional)
- 2.5 tablespoons coconut oil (or any other veggie oil)
- About 1 tablespoon water
- About 2 teaspoons essential oil (for scent)
- 4-6 drops of food coloring
- Small jar or bowl
- 12-18 silicone molds
First, mix the dry ingredients (baking soda, Epsom salt, corn starch, and citric acid) together in a large bowl. Use the whisk to make sure the mixture is clump-free. Baking soda, also known as sodium bicarbonate, is a key ingredient in this bathtub explosion: When the high pH powder reacts with a low pH acid, it produces carbon dioxide bubbles. Remember those baking soda and vinegar volcanoes you made in elementary school? Citric acid takes the place of vinegar in this chemical equation, but it doesn't react with sodium bicarbonate until it gets wet. If you want, you can add visual decorations like biodegradable glitter into the mix. Just don't use regular-old craft glitter, because it's no good for our friends in the ocean.
Now mix up the wet ingredients (oil, water, essential oil, and food coloring). The easiest way to get this party started is to put them in a jar and shake them up. This is the step where you need to make some important decisions about scent. You can tweak quantity to suit your taste, but you should use about two teaspoons total of essential oil or perfume. Try cinnamon, cocoa, peppermint, or coffee scents for the winter holidays (or a combination of all four to make a mocha-licious bath). Or go with something classic, like a spa-like eucalyptus and lavender mix or a straight-up sugary hit of vanilla extract. The possibilities are truly endless. It's also time to make decisions about color. We recommend sticking to a single hue to avoid accidentally muddying the bath waters. Stick to something like 4-6 drops of food coloring total, but feel free to mix up different pigments.
Slowly add the liquid to the dry mixture. Really slowly. Like a teaspoon at a time. Whisk as you go, and slow down if things start to look fizzy. You should end up with a mixture that just barely clumps together, like damp sand.
Stuff that stuff into your silicone molds, ASAP. You don't want the mix to dry out while it's still in the bowl, which is why you should make sure you have enough molds to make a dozen or more bombs at once. Press the mixture down firmly into your silicone molds of choice.
Let the bath bombs dry. If your mold has a lot of details in it, you might just want to give them a whole day to be safe. Then pop them out.
Throw one into the tub and enjoy the explosive fruits of your labor. Bag the rest up in cellophane and make your friends and family love you forever.