RE: Air brush on butter cream cake?

Not sure I fully understand your question, especially about the ruffles. But you can airbrush on a firm buttercream cake. Here is a video that explains…. https://youtu.be/Z-7U_-LKKFc
Here is another tutorial that’s a little more involved. https://youtu.be/6euKTK3hbAQ

Creativity is God's gift to us. Using our creativity is our gift back to God. Clarky's Cakes 😎