In a large mixing bowl combine baking soda, citric acid and cornstarch.
Melt coconut oil.
Combine coconut oil, baby bubble bath, and essential oils.
Add wet ingredients to dry ingredients. Mix thoroughly.
Add the calendula flowers.
Spray the mixture with the witch hazel until the mixture lumps together. To test; squeeze the mixture in your hands, if it crumbles, add more witch hazel. If it stays together, then it's ready to mold.
Finally, fill the skull mold with the mixture and press tightly. Place a paper towel on one hand and flip the mold onto the paper towel. Place the bath bomb on the counter to set overnight.