tips for cleaning gloss paint off of window pane?

Higher gloss paint doesn't adhere well to glass, i would get a 4" wallpaper scraper. It's basically having a 4" razor instead of a 1" blade. You'll have it off in no time.

Cleaning Gloss Paint

As noted in the other tip, carefully cut through the paint as close to the frame as you can get with a single edge razor blade without damaging the frame. Next, buy the tool that clamps a single edge razor blade so that you can safely use it. Now, you can shave off the paint without worrying about solvents, etc. Just be very careful with the tool.

Single edge razor blade very carefully. You do not want to use any kind of solvent as it will attack the good paint. First cut the edge along the frame. Now lay the blade flat to the glass and shave to the cut line. This will take time, but it will work. Don't rush or you will screw it up.

I'm assuming someone painted the brass. You can use a paint stripper and follow the directions on the product. This is a big project. When the paint is off the brass will be tarnished. Use brass polish to restore the metal. This is also a big project. If you want it to stay bright spray it with a can of clear laquer.