I have the same problem. Have you tried cleaning yours? I have painted an old one but I used the wrong color and ruined it.
With seeing pictures, my guess is the dullness is more than likely from rain and its deposits. I would clean with a mild soap on a soft sponge. I use Dawn blue dish washing liquid for everything like this, to cut the build up.
Regular window cleaner should also work.
If washing like Becky suggested doesn't bring it back, try buffing it with any cheap toothpaste and a soft cloth. This works on restoring car headlights and will probably work on your piece. The toothpaste has a very mild abrasive which cleans and buffing it with the cloth should polish your gazing ball.
Becky, Debi -- I'll try both = thanks. I have tried washing it but not with Dawn - which seems to have numerous uses.
@Arlene, please let us know what works for future reference.
I "resurfaced" my ball this summer by gluing on the glass stones you can get at Dollar Tree. I used silcone caulk to attach the stones all over the ball. I love it!
@Bwarner50 I may do this as a last resort - thanks but really want to restore the luster if possible.
You can get stuff specifically restoring headlights at an automotive store.
I'll try this -- thanks Eileen.
Maybe some wax like polishing furniture and I just thought about using some rain X afterwards to protect the finish.
Hope it helps !