Remember to use painters tape to protect the mirror while sanding and painting.
I'm using a course sand paper because the finish is high gloss and it looks like it has been sealed. Depending on the finish of your mirror, all we are trying to do is ruff up finish so the paint you decide to use will grab on to frame. Now I will head to the garage to look for sand paper. This could be an adventure all on it's own. If I do not return.....someone please notify my better half that I'm somewhere in the North/East corner.