We all like to see our antique lamps sparkle and shine. Sometimes we may be tempted to do something that eventually produces unwanted results. Begin with a thorough cleaning to avoid applying anything over surface grime. Many times it is the presence of grime that creates a dull appearance. But before beginning, inspect the globe carefully and check for any hairline cracks.
Wash the lamp with warm, soapy water. When cracks are present in glass globes, apply pressure sparingly, moving gently across the surface, going in the same direction of any crack, and avoid pressing inward (as in squeezing the globe) which could compress the glass and cause the crack to spread.
Remove dust, dirt, and grease film, and then rinse with warm water. A dab of the soap you are using applied directly to stubborn spots can help to release the build-up. Full-strength white vinegar can also be used. Employ nothing more rigid than your fingernail to rub really difficult spots.
Rinse thoroughly and allow to dry completely. Use rubbing alcohol or white vinegar and wipe to remove any soap film, first testing a small and inconspicuous area of any painted artwork to ensure its integrity. Set aside and allow to air-dry.
At this point, a coat of clear lacquer or spray may serve to protect the painted globe and provide the bright, shiny surface you wish to achieve. While this is a relatively simple procedure when disassembled in the shop, lamps on display in the home are a different situation. The gentle application of wax may be a better solution, and any name-brand carnauba wax will suffice. Just observe the same precautions as mentioned previously for cleaning.
One simple thing I try to remember when working with vintage and antique items: Less Is Best.