Recently, I was out metal detecting and discovered a milk glass jar lid insert unlike any I've seen before, and I'm having trouble finding anything out about it, what it was used for, what time period it may have been used, etc. It's a 2 inch glass insert, still with part of the matching zinc lid on it. I think it's one of the coolest finds I've ever made, but would love any help at all on getting more information, pictures if what it might have been used for, etc.
Here is a picture of it, with the zinc portion, next to a regular size white glass insert like you would typically find for most mason or ball type jars.
There is no embossing on it at all. It's completely free of markings. At least now I know what they are called and what to look for. Until I found this, I never knew these existed. Now I need to find a jar to match it up with so I can have a complete display.