Screwdriver underneath and a hammer is my only suggestion. Picture w/help.

try a little squeeze of water at the edge of the tiles and perhaps it will soften the glue and then you can take Slow's suggestion and use the screwdriver and hammer at an angle (almost horizontal). Since you are covering the area with mirror any boo boos won't show. Good luck

A friend of mine came over and made the job easy for me. He was able to pry the architectural piece that was originally placed on a wood plaque, then painted to look all like one piece. This was the part I was after. The mosaic was on bottom wood plaque. I don't know why I didn't think of this in the beginning and therefore wasted time trying to pry off the tiles, while getting a dry grout facial at the same time !

These older architectural pieces like corbels and cornices are sold for a lot of money on eBay, and I wanted to save it badly, so I know I will be able to place it on another wood plaque in the future and make my mirror project.

Thanks for the water tip. I never gave that any thought. If I run into this situation again I will give it a try. Thanks again:)