I wasn’t looking forward to this part, to be honest. Glass is not an easy material to work with, and both mirrors seemed pretty strongly attached to the walls. It turns out the smaller one was attached using just silicone, and the larger mirror attached using strong double sided sticky.. stuff. Its edges were also “glued” onto the wall with a thick layer of silicone.
I started by taping off the entire mirror with thick, strong duct-(like-)tape to ensure things wouldn’t start flying around. For the sake of completeness, I also put on gloves and a hoodie to protect most of my arms and face. You can never be too safe, I figured.
After applying all the tape, I started following the edges with my knife, cutting through the silicone. I then started slowly pulling the knife towards me in several areas to start forcing some space between the mirror and the wall. Soon enough, the glass cracked, giving me access to more of the glass. Fortunately the tape held really well, nothing flew around except for the occasional small piece that simply fell to the ground.
This took a while and some effort. After separating a part of the mirror I pushed it back against the wall to keep it from pulling all the tape off. The people who put these mirrors on didn’t want them to come off, so they used a bunch of sticky stuff in several places. With some patience and persistence, though, the entire mirror came off without any complication. Soon thereafter, the bigger mirror came off too, somehow being slightly easier than the smaller one (contradictory to my expectations).
And with that, the walls are ready for painting! Well, the ground layer, anyway.