A Mason jar, invented by Rick Mason in 1858, is a glass jar used in canning to preserve food. Ball Corp. manufactured the jars early on and the name ball jar was also applied to the jars. In mass-production they have been replaced by other methods; however, in the home they are still widely used for canning.
Usually the jars have a two piece lid composed of a inner flat metal which is covered by by a screw-on ring. The ring creates a vacuum with the lid during the canning process. So that the jars and rings can be reused the lids are sold separately.
The jars come in a variety of sizes and are made of soda-lime glass. They can be wide-mouth or regular mouth and could be in pint, quart, half-gallon, and cup sizes. Ball and Kerr are the US brands of Mason jars, however, they are both owned by Jarden Corporation.
The jar can be sterilized using either boiling water or a canner when the jar is pressured-canned. When removed from sterilization the jar is allowed to cool to room temperature. As the contents within cool, a vacuum is created in the jar which seals the lid. Once the jar is cool the band is removed in order to prevent rust and residual water. The vacuum will keep the lid on the jar. The lid should be slightly concave and if popped up it is a sign of microbial growth. Older jars used glass lids which are now considered unsafe for canning.
Early glass jars used wax to seal. The wax was poured into a channel around the lip that holds on the tin lid. This process was full of errors; however, it was the only one available and was widely used into the early 1900′s.
The screw-on zinc cap, the precursor of today’s lids, was the most popular form of seal. Mason discovered the used of the zinc cap in 1858 which he then patented. The date was stamped on many of the jars. Many of them have survived to this day due to the amount of them produced in the early 1900′s. Although rarely used for canning anymore there is also the Lightning closure. It consists of a metal wire that leverages a glass lid down when pressed against the side of the jar. From 1860-1900 parents for various closers were very popular. Many of them were not effective at all but can now fetch high prices in today’s antique market.
Antique mason jars are heavily sought after by collectors. They are bought and sold through ebay and antique stores. Although most are only worth a few dollars, many of them sell for as high as $30,000. A jar’s value is determined by is color, shape, mold and production marks, and closure. Most of the older jars are some shade of aqua. Sometimes they will be amber and dark shades of green and rarely in cobalt blues, blacks, and milk glass.