Okay, I have only used royal icing on my dummy cakes but I'd like to do a dummy cake in BC because I'm wanting to practice a cake I need to make in the near future and since it will be completely in buttercream I feel like I'll get a better feel for it if I practice it in BC as well.....okay, my question is, once I practice it, can I just use dishdetergent to wash it and it will be fine to use royal the next time?? I'm concerned that there might be a greasy residue left and that I won't be able to use royal on my dummy again. Any advice??

Yes you can use buttercream on your dummy cakes... Will you be able to do royal next time NO... Your going to have to get another dummy just for that.... YOU can go to your craft store and just get cheap foam to play on also...

I would think that if you use the dummy with buttercream...then wash it real good, let dry and cover with contact paper, then you could use the royal icing on that!