Hi Greetings from the UK!
On my 7th attempt at making bath bombs and each time I think I have mastered them until they begin to crack after several hours.
My current dry ingredients are Citric Acid, Baking Soda, Corn Starch & Epsom Salts.
My wet ingredients are essential oil, coconut oil and food coloring.
I have tweaked the recipe and process each time but still at the end they are cracking.