Stomachers are a triangular and stiff piece of fabric that is used to connect the two sides of a gown or jack around the front. While this clothing panel may have begun as a functional implement, the 18th century gave rise to it as a fashionable piece. Robes a la francaise were known as open gowns due to the fact that they were "open" to reveal the stomacher. Stomachers could be sewn into the garment or they were attached to the reverse of the bodice and could be removed. The overall effect displayed a perfectly flat chest, for a ladies' midsection should be smooth and almost cone-like. These accoutrement's were usually lavishly adorned with embroidery, ribbons, or even fancy jewels. In the middle of the century there was a trend for rows of bows descending the stomacher, these were called en échelle or ladders. Judging by her portraits, Madame de Pompadour was quite a fan.
Here are some surviving stomachers which show just how elegant and amazing these accessories could be.