pot metal

an alloy of copper and lead, formerly used for making plumbing fixtures, bearings, etc.

cast iron of a quality suitable for making pots.

a low-grade nonferrous alloy used for die casting.

Glassmaking.

Origin of pot metal

First recorded in 1685–95

To give satisfactory colour the best of pot-metal glass is essential.

Windows, A Book About Stained & Painted Glass |Lewis F. Day
Observe that this yellow stain is neither an enamel nor a pot-metal colour, but literally a stain, the only stain used upon glass.

Windows, A Book About Stained & Painted Glass |Lewis F. Day
The joyous sparkling tone of Tours lights proves a skillful use of pot-metal yellow.

How France Built Her Cathedrals |Elizabeth Boyle O'Reilly
Here the transparent glass is the window; and the design, whether in pot-metal or in enamel, shows more or less against the clear.

Windows, A Book About Stained & Painted Glass |Lewis F. Day

The pieces that are yellow all over may, I think, be assumed to be pot-metal.

Stained Glass of the Middle Ages in England and France |Hugh Arnold