The Kerr Economy and Kerr Self Sealing jars were developed in 1903 by Alexander H. Kerr, who founded the Hermetic Fruit Jar Company that year. Kerr utilised the patents of Julius Landsberger from San Francisco for a metal lid with a permanently fastened composition gasket. These jars were a milestone for home preserving. The Economy jar had a wide mouth for easy use. In 1915, Kerr made a smaller, flat metal disc lid. It fit on top of a Mason jar and could be used with other canning jars.
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. If the finish on the base is smooth on the lip of the jar, it usually means the jar was machine-made after 1915. If the jar is rough and jagged at the base, it was machine-made between the early 1900s to 1930.
Check for mould seams. Jars that were not machine-made have other characteristics. Jars that were free blown without the use of a mould were finished by hand. These jars typically have a number embossed on the bottom called "mould numbers." It usually referred to the glass blower and his team. If there is a mould seam it means the jar was made after 1915.
Check for the style of the jar. If it has small scars on the bottom and has a modern design, it was probably made after 1930, when machines were more efficient.
Look for additional information to indicate modern Kerr jars. Today's modern Kerr jars are all machine-made. Typically embossed on the jar is the date of manufacture, plant location, job number, and other information.
The Kerr lids have gone through several evolutions since 1903 and should never be reused for canning. They are supposed to be used only once and then discarded.