Howdy EfEmDee and everybody else,
It's always fun finding a cache of jars...no telling what treasure you may end up with!
Gunther is right, very "generally" WWI is considered by many to be the 'cutoff' date for manganese use. But for many reasons, we sometimes see jars even into the 50s and 60s that turn purple instead of yellowish suggesting manganese in the glass.
Mainly it was impure cullet though that caused this. Cullet is broken glass that must be added to the raw material glass batch in order to make it melt properly. The cullet acts somewhat like a catalyst and gets everything going. Cullet sources could be almost anything glass (bottles, jars, window glass, etc) so it would be extremely difficult to control the purity or manganese content of the cullet itself.
Definitely a nice way to get into jar collecting! And personally, for home canning use, I trust the older jars moreso than their new counterparts. The glass is usually much thicker in the older jars, and so long as the lip is chip free, they'll seal just as well today as they did 100 years ago! []
Bob
It's always fun finding a cache of jars...no telling what treasure you may end up with!
Gunther is right, very "generally" WWI is considered by many to be the 'cutoff' date for manganese use. But for many reasons, we sometimes see jars even into the 50s and 60s that turn purple instead of yellowish suggesting manganese in the glass.
Mainly it was impure cullet though that caused this. Cullet is broken glass that must be added to the raw material glass batch in order to make it melt properly. The cullet acts somewhat like a catalyst and gets everything going. Cullet sources could be almost anything glass (bottles, jars, window glass, etc) so it would be extremely difficult to control the purity or manganese content of the cullet itself.
Definitely a nice way to get into jar collecting! And personally, for home canning use, I trust the older jars moreso than their new counterparts. The glass is usually much thicker in the older jars, and so long as the lip is chip free, they'll seal just as well today as they did 100 years ago! []
Bob