ABSTRACT
A liner backing is used within a cap to provide a cushion between the cap and the glass finish. When compressed it is the critical element contributing to a successful hermetic seal. There is a clear difference between a liner and a gasket in the industrial literature: a liner is a disc which covers the entire inside surface of the metal cap, protecting the cap surface, and extending over the sealing surface. A gasket is a ring only of sufficient size to cover the sealing surface. The inner surface of the cap is unprotected except by the lacquer. Gaskets were usually of rubber, both as separate pieces and as flowin compounds. Other materials, such as composition cork, found occasional use. For home canning rubber gaskets with tabs were used with glass lidded jars and Chase zinc screw caps on Mason jars. The tabs on the gaskets for the Chase caps were removed for the duration of World War II.
