Sift the baking soda and citric acid into a bowl and mix well. Add the carrier oil and essential oils (plus any colouring if you are using it). Use your hands to combine the mixture, rubbing it between your fingers to evenly disperse the wet ingredients. You’ll know your mixture is ready when it sticks together/packs down and can keep its shape. It will still look kind of dry, but if you take a handful of the mixture and squeeze it, it should pack easily into a ball. If your mixture is too dry add a few more drops of carrier oil and mix again.
Now grab a mould and place a couple of spoonfulls of mixture in it. Push the mixture down firmly to cover the bottom of the mould as this will ensure your mixture is compacted well and cause less breakage. If you are using a soft silicone mould, be careful not to push so hard that your push the mould out of shape. Continue to fill your mould, pushing down the mixture and compacting it into place. Compaction is an important step as it may mean the difference between hard or crumbly ‘bombs’ once they are dry.
Set the bath bombs aside to air dry for 24-72 hours. If humidity is high at the time you make your bath bombs, consider drying your bath bombs in the oven on the lowest setting with the fan on for an hour or so.
When they are sufficiently hardened, they should release from your moulds fairly easily, if they are still wet, they will not fall out with ease.
Notes
Wearing gloves is recommended.Store in a plastic zip-lock bag.