Activated charcoal is a great colourant for soap. From grey through to black it is a versatile additive to have in your kit.
Colloidal Oatmeal is an incredibly soothing additive
French clay is gently exfoliating and adds a silica element which can help with locking in moisture.
Titanium dioxide a brightener, great to use when adding micas
Tussah silk adds an incredible silkiness to the soap lather
Pumice the great exfoliant!