Is it possible to do "marbeling" on a rolled buttercream cookie? Seems like it would only work if the cookie was wet.
I can only think of two ways to do this with RBC, and since I've never used the medium, it's just a guess! One: Don't completely mix in the food color. Leave it streaky, then roll out. Two: lay strips of different color icing next to each other. Twist together, then roll-out. My best advise is to experiment. Hopefully, someone else will be able to give you a better answer!
Is this like what you are talking about:
If so, this is what I was told about how it was done:
"It took awhile, but it was fun. I just colored some RBC the different solid colors...red, orange, yellow, green. I added some cocoa to make the colors richer (could have used brown food coloring, but I was tired of staining my hands at that point). I then broke off little teeny pieces of each colors and sort of smushed them all into a ball, then rolled and cut. I rerolled the scraps and those definitely had a more marbelized effect the more I worked with it...I'm not sure which I liked better. Both effects were pretty, but different. I brushed on a little gold Luster Dust afterwards too. Let me know if you have any other questions. It really was easy...just time consuming."
I was also told of this technique with fondant. I would think it would probably work the same with rolled buttercream.
"I marble my fondant by taking two or three colors, rolling it out in log shape and kind of braiding it around the other color. Then I just roll out with a rolling pin until I get the desired look. It's really easy!"