Nick,

    I had to do the same, it had bondo or similar under the paint to fill the imperfections, plus the carbon black layer which over the years becomes damp and then detaches, so much of the top layer paint stripped with careful use of a thin wallpaper stripper blade. Where it was solid I used the fine wet and dry to flatten it down but watch the top layer of glass. I would say 75% of the paint lifted with no problem. 

    Rich T.