These are so much fun. They fizz in your bathtub!!
1 cup Citric Acid (available at home brewery supply stores, health food stores, and soap making suppliers.)
1 C Baking Soda
½ C corn starch
½ C Light Oil (olive, grape seed, sunflower, etc)
Epsom Salts, fragrance*, herbs, or coloring if desired.
Mix all ingredients together to form a slightly wet powder. The only trick here is to get the mixture wet enough to hold together without setting off the citric acid fizz. If you squeeze some of the mixture in your fist, the powder should hold its shape after you open your hand. It should be the consistency of sand you would use to make a sand castle. If your mixture is too dry, add additional oil very slowly until you obtain the desired consistency.
Pack into molds and let sit for several hours. I personally use muffin tins or plastic Easter eggs. You can purchase bath bomb molds online, but in the spirit of being as green as possible, I just use whatever I already have on hand.
That's it! These are a huge hit as gifts.
*I recommend using essential oils rather than fragrance oils. My current favorite blend contains lemon, rosemary, and gardenia essential oils. I don't have a set amount of each oil that I use, but I typically will do highest amount of lemon oil followed by a little less rosemary and even less gardenia. So perhaps something like 10 drops of lemon, 7 drops of rosemary, and 5 drops of gardenia. It smells wonderful.