Lamps made from stained glass are a familiar sight today. They are often called Tiffany lamps but that is a misnomer. An authentic Tiffany lamp is one manufactured by the Louis Comfort Tiffany Studios in New York City between the early 1850s and the mid 1930s. Real Tiffany lamps were expensive, making them available mainly to the wealthy. They can still be viewed in the White House as well as Mark Twain's home in Hartford, Connecticut. Today, genuine Tiffanys are scarce, increasing their worth exponentially.
Learn about Tiffany lamps. Study books like Nancy McClelland's "The Lamps of Louis Comfort Tiffany." If possible, visit museums featuring Tiffany's work, including The Morse Museum of Modern Art in Winter Park, Florida. Talk to antique dealers and collectors whose area of expertise is authentic Tiffanys. Check out websites like Antiquetiffanylamps.com.
Study the lamp for identifying marks. Check the lamp for maker's marks, that is a mark of some sort identifying the piece as a real Tiffany. An authentic Tiffany might have a narrow bronze tag soldered to the bottom rim of the shade with TIFFANY STUDIOS NEW YORK stamped on it. Another mark Tiffany sometimes used were the initials L.C.T. CO. impressed on the bottom of the lamp's base. Look to see that all letters are arranged in a straight line and all in capitals. If not, the lamp is most likely a fake, manufactured after 1930.
Examine the glass shade. Look for variations and bubbles in the texture of the glass. True Tiffany lamps were handcrafted, and each piece of glass was unique and contained imperfections. Factory produced lamps will be smooth on the outside because the glass is machine made. Notice the pattern. True Tiffany patterns often reflected things in nature like trees, flowers, hummingbirds and even insects.
Inspect the craftsmanship. Tiffany used only the best materials, such as handcrafted glass for the shades and solid bronze for the base. A lamp that is cheaply put together with uneven soldering and a lightweight metal base is likely a fake that has been mass produced.