Corsets - the Shape of a Lady

The corset was an essential part of a woman's attire in the 18th century but the term "corset" was not invented until the 19th century - before that it was known as a "stay". The stay was such an important part of a woman's attire that even very poor women were supposed to wear them - prostitutes would wear loose stays to signal that it could easily be removed if a customer wished it. The purpose of the corset was to create a small waist as well as tightening the bust and enhance the breast - almost like a push-up bra. In the 18th century the stay was considered a part of a lady's underwear but it had previously been a part of the visible dress. Now, it was worn over a shift or a chemise and so was not in direct contact with the skin.
At the very beginning of the 18th century the stays were long in the front (forming a "V") but remarkably shorter at the back.

To make sure that the corset would stay in place and constantly provide the lady with the desired small waist it had to be made out of rather hard materials. A gentlewoman's stay would consist of several layers of linen which had been stiffened with a sort of paste. Besides, several "channels" would be hand-sewn into the linen - the channels would be stiffened with whalebone. Towards the end of the 18th century the old-fashioned stays - that would be very stiff and painful to wear - had been replaced by a more relaxed style that would put focus on the breasts. Horace Walpole noted that a lady had been severely bruised by her corset!
Even though the stay was considered an integrated piece of underwear it would still be lavishly decorated with silks. When wearing a corset a woman could not bend forwards at the waist but it was actually very healthy - it would mean that women would always lift with their legs thus sparing their backs.

Pretty example of an 18th century stay (Metropolitan Museum of Art)

A rather good description of how a stay was laced

                

                   French, between 1735-1770