They used some sort of mastic (adhesive) for the tile obviously. You would need to use a scraper and scrape it all off. Sides, probably 1/2" away from the insert and top at that current mastic line is what I would do.

Unfortunately, it won't scape off without leaving residue and taking off the black paint.

You can always repaint the fireplace if some of the black paint comes off while scraping. Use heat proof paint, intended for refurbishing older fireplace inserts like yours. You would probably have to paint the entire surround for an even, intentional look.

I am concerned the tile won't adhere properly to the metal, but I sure cannot leave it exposed as it stands. Scraping it off took a lot of the black finish off.

Keep in mind some sort of edge or bullnose to finish off the tile. Make sure to install it properly - with the correct trowel size and mastics etc - not blobs of adhesive. As long as the surface is prepped properly, you should have no problem. The other tile stayed on there just fine.

Good luck!

Lori,

I am assuming you will be overlapping the wall and black metal with your tile. There is not enough metal area to be concerned about the adherence. Thin-set will work just fine for typical tile. With that said, just ask whoever you buy the tile from what the appropriate adhesive would be for your application.