Rather than taping over air bubbles in your photoresist film, which can be time-consuming, use a non-PVC sandcarving film such as LazerMask. This type of sandcarving film does not require you to tape over air bubbles or use a wire wheel brush; however, if you are using standard photoresist film and have an air bubble in the artwork image, using a wire wheel brush is necessary and speeds up the process in comparison to taping.
Simply roll the brush over the design and press down with your fingers to remove the trapped air. Note that if the air bubble is in the blue or red part of the sandcarving film, you do not need to cover it with tape.
-Liz Haas, Rayzist