In a medium to large bowl, combine baking soda, citric acid, kaolin clay, and mica. Mix ingredients thoroughly. Be sure to break down any clumps. I find it easiest to sift the ingredients.
Add Rosemary and Spearmint essential oils to dry ingredients.
Slowly pour witch hazel into dry mixture while simultaneously mixing with whisk. Mix until it can be firmly squeezed and hold together.
Pack three tablespoons of mixture into bath bomb press then press onto table or level surface.
Let shower steamers dry for at least 5 hours then shrink-wrap or put in airtight container.