08/31/2026
Monday Moment 🤍
Ever pick up an old zinc canning jar lid and wonder why there’s a piece of white glass tucked inside?
That little insert is commonly called a milk-glass liner, and it had a very important job.
When zinc screw-on lids became popular on canning jars in the late 1800s and early 1900s, food could react with the metal. The glass liner created a barrier between the contents of the jar and the zinc lid, helping keep the food from coming into direct contact with the metal.
The lid still needed a rubber sealing ring to create the actual seal — the milk glass wasn’t the gasket. It was there to protect what was inside.
Eventually, newer two-piece metal canning lids made the old zinc lids and glass liners largely obsolete, but plenty of them survived.
And here’s the fun part for us junkers: sometimes you’ll find an old zinc lid without its liner…and sometimes you’ll find one of those little white glass discs all by itself and have absolutely no idea what it once belonged to. 😉
Just another one of those everyday objects that makes a whole lot more sense once you know the story behind it. ❤️ HAPPY MONDAY!
