I'm going to be making a cake later this month where bottom tier is will be the ocean. The cake will be covered in fondant and I want to pipe waves. I want to use buttercream because i will already have buttercream for icing the cake and I don't really wanna make a batch of royal icing just for the waves.

I've never actually put buttercream on top of fondant before and I wonder if it will leave grease stains that spread beyond the edge of the buttercream, if that makes sense. So, can I get away with that or MUST I use royal icing?

I've made waves on fondant using buttercream and never seen any seeping grease stains.

Rae