In a large bowl, mix baking soda, citric acid, corn starch and sea salts with your hands until well combined.
Add coconut oil, essential oil and coloring and immediately mix to stop any reaction occurring from the wet ingredients blending with the citric acid.
Continue to mix with your hands until color evenly distributed throughout.
Once mixture is adequately combined it should clump in your hands when you squeeze it.
Pack both sides of mold to overflowing.
Join both sides of the mold and gently shift back and forth in small movements while pressing each side of the mold together.
Tap one side of the mold and remove it, then do the same with the other side.
Set bath bombs on a cookie sheet or other similar surface to dry for 8 or more hours.
Notes
If not using right away, gently store in plastic wrap. Because of the citric acid these bath bombs contain they are very susceptible to humidity and moisture.
Yields: 5-6 Bath Bombs (Sprinkle any excess mixture into your next bath)
Recipe by Today I Might... at http://www.todayimight.com/projects/make-bath-bombs/