Dating mason jars
In order to save precious metals like tin and steel for war purposes, people reverted to mason jars to keep food tightly sealed.
Even after the war, mason jars were still being used but this time, for canning and preserving fruits, which became a big fad in the 1950s.
During World War II, glassmakers shifted to selenium as supply for manganese dioxide was limited.
Thus purple jars can be considered to have been made before World War II.
Very rare mason jars have recently fetched up to a thousand dollars, while antique ones can be priced for up to a couple of hundreds online.