All of Paul Sahlin Tiffany's stained glass lamps are real glass. Each stained glass shade is hand foiled with copper foil, and then soldered together by craftsmen. No two pieces of glass are exactly alike. They do have some blisters, seeds, lines, and variations in the surface. These are not defects, but are simply characteristic of hand crafted stained glass.
The art of stained glass is the process of hand cutting sheets of different colored glass in a specific pattern to create a unique design. The glass which is used to make stained glass items has special properties in order to give it the neccessary strength and durability.
All glass is made of sand melted down into a molten state. Stained glass is then poured into sheet form, and hand cut to fit a specific pattern.
"Stained Glass" - glass colored in any of various ways, as of fusing metallic oxides into it, by enameling, by burning pigments into its surface, etc. (webster's definition)
Because of the construction, when a stained glass shade is tapped with an object the resulting sound is deadened and totally different then the sound made by tapping ordinary window glass.