In bowl, place citric acid, baking soda, cornstarch, and oil.
Add approximately 15 drops of the essential oil or essential oil blend of your choice. Use more or less depending on your personal preference.
Mix well with spoon until soft dough is formed. It should have the consistency of damp sand.If the mixture is too wet, try adding a little more baking soda and cornstarch until consistency is correct.
At this point, you may add food coloring, dried herbs, or flower petals to mixture.
Place mixture in silicone molds. Let sit 24 hours before removing from mold.
To use, drop in tub or shower and allow to dissolve.