Tiny air bubbles are common in freshly mixed icing because of the whipping motion used to make it. To prevent the bubbles, let freshly mixed icing rest for 10 minutes before tinting, or mix the icing on very low speed for a few minutes to coax out the air bubbles. If bubbles are still visible on the surface of your cookie after flooding, pop them with the tip of a toothpick or a clean needle.