How old is this clear (mason fruit?) jar with empty keystone
Trying to date this jar. Initial research says the empty keystone is for Rosso who was a wholesaler and not a manufacturer. This particular keystone seems to be tied to mason fruit jars as well, although I don't know if Mason would be a general term or a brand here. It has a horizontal diamond pattern design around the top & bottom of the body of the jar. The bottom of the jar is marked: (top line) JM 4616; (center line) 7, empty keystone. Any idea what the JM or numbers mean and what period this is from? Thanks!