I picked up a couple of old blue glass Ball Mason jars at the Goodwill yesterday. Two of them have number marks on the bottom. I heard somewhere that you can date the jar by these marks but I can't figure out how. Anyone heard this before and know how to crack the code?
The jars are pretty cool- one is huge, about 1.5 qts- and they all have their original zinc or glass bail lids. I love using them for storing dry goods; they're so much nicer to use than plastic containers.