The Mid 1770s (1774 - 1776)
Seated Woman in Profile, 1774; MMA 1975.1.655
The woman is wearing a striped jacket and petticoat; the jacket's sleeves have turned-up cuffs and are below the elbow, and her apron is as long as the petticoat. Her kerchief is worn over the jacket, and her cap is tightly fitted to her head, with a double ruffle around it.
Detail of "Le Bain", 1774; MMA 33.56.32
This servant woman is wearing a long European-style bibbed apron, which hides her bodice. Her gown is pulled up over a flounced petticoat. The stripes on her sleeves run horizontally, and her sleeves cup her elbows, with ruched cuffs and bows. She wears a ribbon choker.
The Music Party, Louis Rolland Trinquiesse, 1774; Alte Pinakothek
The young woman in the foreground is also wearing a polonaise with a bow sewn to the place where the skirt has been pulled up. Her elbow-length sleeves have box-pleated trim as a cuff, with a bow sewn to the inside of the elbow over the trim. The box-pleated trim is along the edge of the skirt, and up the front of the bodice as well. There is a delicate fly fringe around the hem of the flounce on the petticoat, and a transparent, short flounce around the outside of the gown's skirt, the bottom of the sleeves, and around the neckline.
Portrait of an Elderly Woman with her Daughter, Vallayer-Coster, 1775; Bowes Museum, Barnard Castle B.M.329
The mother, on the left, is wearing a sacque with a gathered or pleated trim that meanders down the robings and the front of the skirt of her gown, across the stomacher in rows, around the bottom of the petticoat, and above the ruffles on the sleeve. There is a large bow on the top of her stomacher, and her kerchief is small enough to cross at the base of her throat and reveal her chest. Her daughter, on the other hand, is much more modern: the trim on her sleeves is ruched, and her bodice meets at the top of the stomacher and runs down to the side of her waist. Her gown is probably a polonaise, trimmed all the way around, with a bow sewn to the place where the skirt is rétroussée.
Detail of "Two Ladies in the Newest Dress", 1775; LWL 775.06.01.02
Both of these ladies are wearing rétroussée gowns; the one on the left is an anglaise and the one on the right is a sacque. (Or a piémontaise - the fashion plate of which, you will note, is from 1778 but depicting a dress of 1775.) Both also wear ribbon chokers and have a row of meandering gathered trim at the bottom of their petticoats: the lady in the sacque, however, has more trim creating a diamond pattern on the front of her petticoat and between two rows of gathered trim down the front of her skirts. She also has trim on the lower part of her robings and on her flared cuffs. The lady in the anglaise has three rows of trim on her sleeves and a very small self-fabric ruffle on the end. She may also have a small pin holding the back of her kerchief to her gown.
Detail of "A pleasing method of rouzing the doctor", 1775; LWL 775.08.31.01+
This serving woman's bodice does not have a stomacher, but does not actually close center front: it laces over her stays, with her kerchief tucked into the lacing and under the fronts. Her sleeves are shorter than those in the portraits of fashionable women, but are trimmed with box-pleated dress fabric.
Detail of "A Bagnigge Wells scene", 1776; LWL 776.00.00.28+
This fashionable woman is wearing a gown with narrow, gathered trim on the robings and down and across the stomacher in a T-shape, with slightly broader, ruched trim down the front of the skirts and across the front of her petticoat. There is a bow on each of her (flounced) sleeves, and at the top of her stomacher.
Mme de Saint-Maurice, Joseph Siffred Duplessis, 1776; MMA 69.161
Madame is dressed en déshabille, in a peignoir and a whiteworked muslin apron over a pink silk petticoat. The peignoir is attached to some sort of sleeveless underbodice with a compère front.
Detail of Queen Charlotte with Charlotte, Princess Royal, Benjamin West, 1776; Royal Collection RCIN 404573
Queen Charlotte is wearing a gown which closes at the neckline at center front with a large bow, and falls away to the hips. There is a kind of flat, broad collar around the neckline of the gown. The stomacher is trimmed down the front with a gathered strip, and the collar, neckline, and bodice fronts are trimmed with a flounce. Her sleeves have curved gauze cuffs, with bows on the inside of the elbow. She is also wearing a long muslin apron, a strand of pearls, and a small kerchief, gathered with a ring or pin.
During the middle of the decade, everything began to shift. Nearly all the styles appear in conjunction with each other - triangular stomachers, diamond-shaped stomachers, compère stomachers (I believe that this is the earliest soldily-dated picture I've seen with a compère front). Not only was the older style still worn in general, it was still considered fashionable - although it might be that this was a class-related issue. The triangular stomacher-front appears in prints, which were created by middle or working class artists, while the polonaise-style front appears in portraits, on people who were certainly wearing them when they were painted. There are textual mentions of the polonaise from 1774, but even in 1781 the polonaise had a strong class association.