Tiffany Studios made many lamps of the same design with different glass. Following are four examples of 16″ diameter Colonial table lamps.
The example above was built with striated (streaked) glass. The color is flat and unattractive. I would rate it a 5 on a scale of 1-10.
Example 2 has dichroic (two-color) glass, which is one color unlit and another color lit. The unlit color is awful, a 3. Since I don’t have a photo of it lit, I have no way to determine how nice it might be, but it’s sure to be nicer.
Example 3 is less common, as it’s green. The glass is very nice, with extensive mottling. I would rate it a 9.
The example above has fiery rust and orange mottled glass. It’s a spectacular example that I would rate a 9.8.
If you’re in the market for a Tiffany lamp, check the glass. Sometimes a great example of the same lamp can sell for 2-3 times or more of the value of a lesser example. It isn’t the only criterion you should look at, but it’s certainly important. Buy what you can afford but always stretch for the better examples.