Mix your dry ingredients (baking soda, cornstarch, Epsom salt, and citric acid) together. You can find citric acid most likely around the kitchen aisle with the mason jars and canning supplies.
Mix 5-10 drops of your desired color of food coloring in a spray bottle with water. Make sure your spray bottle has a misting feature because you will need it. Now you want to lightly mist your dry ingredients. I bolded lightly because it is important that you don't over mist. Your mixture will bubble itself up before you even get to use it in the bath. Mist lightly and then mix around, rinse and repeat until you get the desired color. I mixed my ingredients in a 9x13 pan and misted lightly and kind of folded it in like a cake.
Drop-in a few drops at a time of your favorite essential oil and mix around. If you want it to be stronger, drop in a few more drops.
Now that your mixture has its color and scent you are ready to mold your bath fizzies. I used a muffin tin but you can use any type of mold you have available. Fill your molds and allow them to dry for 24 hours. Once your molds are dry you can pop them out and they are ready to give as gifts or use for your own relaxing bath.