Check the jar from top to bottom. The Kerr name will be embossed on the glass. There are some general guidelines to approximate the date of a vintage Kerr jar between 1915 and 1930. The finish on a fruit jar can tell you roughly about the date it was made.

How old are my Kerr canning jars?

Look for the Kerr name, which is embossed onto the surface. Observe the finish of the jar. If the base is smooth at the jars lip, it was made by a machine after 1915. A rough base means the jar was made between 1900 and 1930.

Whats the difference between Ball and Kerr?

The same is true of glass jars. All the arguments about the difference in quality between one brand and another is only perceived differences. The glass is made in the same batch, the only differences are the molds - whether they say Ball or Kerr is only cosmetic.