Glass objects should be eligible for forging, since the temperatures involved in a forge are more than enough to melt and recast glass.

Also, it should be possible to forge pieces of worthless glass together to make decorative ornaments, which are worth either score or can be sold for spare money.

The room of gems in the Castle should never contain worthless glass. (Unspecified whether it should still contain gray stones, or exclusively valuable gems.)

Colored glass frequency corresponds to its real-life frequency; red, orange, and yellow glass are rare; green and brown common, etc.

Shopkeepers will buy identified glass for the same few zorkmids they will buy it unidentified, rather than refusing to buy it, because it makes no sense that they buy it when the player doesn’t know that it’s glass and refuse to when the player does.

Dwarf and gnome kings will never pick up worthless glass or gray stones on the ground (they continue to pick up all valuable gems).

Archeologists (maybe gnomes too) start the game with all valuable and worthless gems (but not gray stones) identified. If this is too powerful, perhaps they only begin the game with all worthless glass identified.

Special room “ruined church” that contains ghosts, pieces of glass scattered around the floor, maybe an altar, maybe a spellbook, and blank paper/scrolls of junk mail scattered around the floor.