Carnations are a great flower for using up any leftover royal icing you may have, because they can be made in almost any color imaginable (florists dye them all sorts of unnatural colors for whatever season's at hand; you should, too!). You'll need a large flower nail, a parchment square for each carnation, a non-toxic glue stick, a Styrofoam block (to act as a third hand), a rose tip #104 or straight tip #150 (specifically called a Carnation tip by Wilton), a piping bag filled with stiff-consistency royal icing in any color you like, and a dusting pouch filled with a 50/50 mix of powdered sugar and cornstarch.
like the rose is prone to do). You can speed up this process by placing the balls under a desk lamp. If you're using tip #104, pipe the first few stand-up petals in the center by holding the wide end of the tip against the ball and moving the tip in an up-and-down motion (tip #150 is symmetrical; it doesn't matter which edge is against the ball).