Cotoss Stained Glass Panel, Tiffany Handcrafted Art Panel is slight heavy than you expected, as it is made of real stained glass.

But when you knock it, it sounds like plastic. That's why?

Because of its special manufacturing process.

Each glass piece is cut by hand, then polish the edge before wrapping the copper foil. The edges of the glass pieces are wrapped with adhesive copper tape (copper foil).
Then putted together in a mould according to the pattern.
At last, using soldering material to weld each glass at a very high temperature.

The Stained glass is Much Heavy than Plastic, and couldn't been burned, normal knife couldn't cut them. Easy to Check it.