Fit the decorating bag with tip 12 and fill 1/2 full with medium constistency icing. Hold the bag and tip at 90° angle, slightly above the surface of your cake.
Pipe dot balloons by squeezing the bag, applying steady even pressure. As the icing begins to build up, raise the tip with it, but keep the tip buried in the icing. Stop squeezing as you bring the end of the tip to the surface. Lift the tip up and pull away from your piped ball. Use the edge of the tip to shave off any point so your ball is nicely rounded.
Add a tip 2 string.