.. steel! In 1856, inventor Bessmer applied new technology to the teeny rings. By this time, women were trusting the metal grommet, and were open and willing to try a new type of metal.
(Featured the new steel grommet on an extant corset. Below, a late Regency/early Victorian corded instead of boned “light” corset with old fashioned shoulders and early metal grommets – the shoulder straps and light boning would die quickly in the late 1850’s)