@Tara_H you can try adding a few drops of PS80 to the bomb before tossing it into the tub. I haven’t tried that but read a post by someone who said it works. I use some PS80 mixed into a paste of water and baking soda to scrub away greasy residue on sinks and tubs.I tend to use quite saturated colours in my soap and haven't had any issues with residue. The only mica traces of any kind are from an early batch of bath bombs which I coloured with mica and also used coconut oil, they leave an unfortunate yellow greasy rim in the bathtub