If I pipe some lines with black royal icing and let them dry, will the black run if I come back and paint inside them with food coloring and vodka?
I didn't know if hitting the black royal icing with the wet vodka would make the black run or not. Or maybe since it's dry it wouldn't? I'm not sure.
it should be fine
It will be fine. That's how I did my stained glass cake.
Once royal icing is dry, it's DRY. When you do floodwork nothing bleeds, right? Same principle applies.