By the 2nd half of the 18th century, the staymaker realized..

… it was the direction of the bones and supporting inside bones that were important, so less seaming was used, and more boning.  These later stays were often covered in plain silk or cotton and were very stiff but subtle in form.  They were shaped using a steam iron.

(Extant: 1765 stays with intricate shaping boning and decorative outer fabric)