Many Ball mason jars have a number printed on the bottom of the jar, but this is a mold number that does not indicate the year of production. Rather, the mold number tells you where the jar was positioned on the glass-making machine that was used to produce it.

How do you date Ball Mason jars?

So if you have some old jars, how do you know their true age? If you have a Ball jar, you can date most of them just by looking at the logo. Every few years, the Ball Manufacturing Co changed the logo and if you compare yours to a reliable chart, you know how old it is.