A trick I use with the CO2 laser when engraving glass is to put a damp paper towel on the surface, it keeps the pieces in place and prevents the micro cracks from becoming too large. You get a much crisper result and don't end up with 10,000 cuts when cleaning up.
If you haven't tried removing the "paint" from the back of a mirror yet, give that a go. It works fantastic and you can even do a multi-color design by etching and filling with acrylic and then etching again. I used cheap dollar store mirrors that were in a picture frame. I suspect higher quality mirrors may have a more metallic coating which can't be removed.