Air bubbles in RI

Air bubbles in royal icing mix are a common but annoying problem. They are formed when air is introduced into the icing.

The bubbles can create icing craters in dried details or unsightly bumps at the top of your crust (see photos below). What starts as a tiny air bubble can quickly become a disastrous dent if you don’t catch it soon enough.
If you notice any air bubbles, pop them with a scribe right away. If you don’t, the air bubble usually pops on its own and leaves a hole in your icing.

It's impossible to get rid of every single bubble in your icing, but there are some strategies you can use to reduce them a lot. Following them should help, but always remember: practice makes progress.

Use the paddle attachment on your mixer instead of whisk attachment. This will allow you to mix your ingredients without incorporating too much air into the icing, causing bubbles. Don't mix your icing for too long or at too high speed - don't go above medium speed on your mixer.
Let it sit. Before you bag your flood icing, allow it to sit in the bowl for a few minutes. The air bubbles will slowly rise to the surface so you can pop them gently with the surface of spatula. The longer you let it sit, the more bubbles you’ll be able to pop.
Massages and helicopters. This may sound ridiculous, but yes: once you place your icing in your piping bags, gently massage the bag to force air bubbles to the top and icing toward the tip. With the bag tied off, you can use the “helicopter method” by gently swinging the bag in a circular motion (like a lasso) to force any remaining air bubbles toward the tied-off end.
Tap the cookie. After you’ve finished applying the icing to the cookie, shake it gently left to right to bring air bubbles to the surface so that you can pop them with a scribe (or a toothpick).
Make the icing thicker. Thicker icing holds bubbles left in your royal icing mix in place so they can’t rise as quickly and won’t poke through the top of your flood.