 Prior to Mason's innovation, jars had a flat, un-threaded top, across which a tin flat lid was laid and sealed with wax.It was messy, unreliable, and unsafe – if the wax was not applied properly it allowed deadly bacteria to thrive in the jar.Mason's easy and re-usable jars made home canning procedure's popular among American settlers, homesteaders, and even in urban homes, but most Mason jars were manufactured by competitors after his patent expired in 1879.