In a large bowl, combine the Epsom salt, cornstarch, baking soda and citric acid. Stir the ingredients together using a whisk.
In a separate small bowl, mix together your wet ingredients: water, fragrance and food coloring.
Now slowly whisk in the wet ingredients to the dry ingredients a little at a time. Don't dump the whole thing in at once because you'll ruin the fizz.
You want to get the mix to a "clumping" consistency. If it seems to be a little dry, add a drop or two of water at a time and continue to mix.
Use your fingers to test the consistency. Pinch a bit between your fingers. Does it stick together? Yes? Then you're ready to put it into your mold.
I fill them to the top and then I slide a butter knife across the top to clean up the excess around the mold.
Get out those sprinkles and start shaking them on! I just put sprinkles on the tops of my bath bombs (which are technically the bottoms).
If you feel like the tops of your bath bombs are still a bit too "powdery," you can always spritz the tops with a little water.
Now you wait. Like an overnight wait. I'd say at least 12-14 hours for sure - 24 hours if you want to be certain that they'll pop out of the molds for you with no problems.
Notes
Mix Wet and Dry Ingredients Gradually: When combining the wet and dry ingredients, it's essential to do so gradually to avoid activating the fizz prematurely. Slowly whisk the wet ingredients into the dry mixture a little at a time, ensuring thorough incorporation without causing excessive fizzing. This gradual approach helps maintain the integrity of the bath bombs' fizzing action and ensures that they retain their shape during the molding process.
Achieve the Right Consistency: The consistency of the bath bomb mixture is crucial for successful molding and fizzing. Aim for a "clumping" consistency where the mixture holds together when squeezed between your fingers. If the mixture seems too dry and crumbly, add a drop or two of water at a time until you reach the desired consistency. Be cautious not to add too much water, as this can cause the mixture to become too wet and lose its ability to hold its shape.
Allow Sufficient Drying Time: Patience is key when making bath bombs, especially when it comes to drying time. After molding the bath bombs, allow them to dry for at least 12–14 hours, preferably overnight, to ensure they are fully set and hardened. If you want to be extra cautious or live in a humid climate, consider allowing them to dry for up to 24 hours. Proper drying time ensures that the bath bombs hold their shape and release their fragrance and fizz effectively when added to the bathwater. Once fully dried, store the bath bombs in an airtight container to preserve their freshness until ready for use.