Mix the dry ingredients first (Epsom salt, baking soda, cornstarch and citric acid), using the whisk. Mix well to ensure there are no clumps.
Distribute evenly into 4 small bowls
If your coconut oil is not in liquid form, melt in microwave for about 30 seconds.
Mix the wet ingredients in a jar, one color at a time. The measurements would be 1 ½ teaspoons coconut oil and ¾ teaspoon water, plus 2 drops of soap colorant. Secure with lid and shake well.
Very slowly add each color of liquid mixture to each bowl of dry mixture, about a few drops at time, while whisking the entire time. If you’re not pouring slowly enough, the mixture will start to fizz and you don’t want that to happen, because then you will need to start over again with all new ingredients.
Once all of the liquid has been poured into the dry mixture, mix very well until the color is consistent.
Fill the molds with the mixture (see process photos for examples). In one half of the egg, use one color to fill halfway, then add another color, stuffing it firmly to fill that half of egg. Repeat this process with the other two colors, filling the other half of the egg.
Secure both parts of the plastic egg together and let set. I always give it about a day, just to be on the safe side.
Carefully release bath bombs from eggs and put into an airtight container, or individual cello bags. The eggs can be tricky to open, so you can carefully and slowly use a butter knife to help open the gap between the two halves of the egg.