I wouldnt cover the stained glass with it as it doesnt need protection and it ptobly would peel off IMO-I dont know a brand of poly with UV protection, sorry!

Thanks, wacky! I've come to the same conclusion about the glass. It's better not to take the chance that it would peel and look horrible. I think the right answer is to paint whatever I use onto the stone beads.

Polyurethane UV protection is only a short term protection - basically yacht varnish will last a few years then start flaking and need sanding down and replacing. Stone seal might be better as it would just fade away over time, rather than flake and could then be rejuvenated with another coat, but I think you'd do better to just leave it be

Here is a link that might be useful: Mosaic Adhesives and Grouts

I ended up getting a crafter's polyurethane from Hobby Lobby because everything I found at Home Depot was for wood. (That's probably the yacht polyurethane you mentioned, african.) It doesn't say anything about UV protection, but I gave up on that idea. All I can do is the best I can do. I'm going to brush it on the stain flowers before I grout. The only thing the bead store was worried about was fading, and even if the stone flowers fade to white, I think it will still look good.