I was wondering if anyone could give me any tips on how to pipe swirls on buttercream?  Does it have to be done with buttercream or can I use royal icing?  Customer wants it very smooth and clean looking.......Cake is setting up in the fridge right now,figured someone out there would have some helpful tips.  Thank you!

AI tend to use an imprinted so that I know exactly where the swirls will be placed and that they will be uniform. Bc or royal - your choice.

So you can use royal icing on buttercream?  I was planning on using an imprint on the cake first and then go over it.

I would use bc, just so I didn't have to make up another batch of something.  Why couldn't you use ri on bc?