To quote Wikipedia:
A mantua (from the French manteuil ) is an article of women's clothing worn in the late 17th century and 18th century. Originally a loose gown, the later mantua was an overgown or robe typically worn over stays, stomacher and a co-ordinating petticoat.Here's the picture actually used in the article.
The earliest mantuas emerged in the late 17th century as a comfortable alternative to the boned bodices and separate skirts then widely worn.
The mantua featured elbow-length, cuffed sleeves, and the overskirt was typically drawn back over the hips to expose the petticoat beneath. In the earliest mantuas, the long trained skirt was allowed to trail.
The mantua was originally a loose gown, rather rectangular in construction. There's a darling example on a 1690s doll that clearly shows its blockiness, the folds on the edges, and how it doesn't even meet in front.
Wikipedia claims that the mantua evolved into formal court dress of the 1700s. Cassidy's research on court dress, however, indicates that only English court dress developed from the front-closing mantua, while French court dress was a fossilized form of earlier 1600s dress, with separate back-fastening boned bodice and skirt. If I recall correctly, in Kendra's class on 18th century dress variations, she traced the sacque (robe à la francaise) back to the early 1700s robe volante. I think the robe volante, with its loose shape and geometrical pattern, came from the mantua when its skirts were not draped back. (I'd welcome corrections on any of this!)
The mantua was originally worn open, showing the separate boned bodice and petticoat beneath. Gradually the boned bodice evolved into stays. From being a complete dress bodice, the fine fabric and decoration was limited to the front, and then vanished from sight as it was covered by a separate stomacher.
Back to the original question. If the time period is right, and the silhouette is similar, why is this portrait of the Duchess of Somerset so clearly not a mantua?
The time period is right, and there are similarities in the silhouette, but there it ends. Compare to this portrait of 1693, which shows a non-informal mantua.
The bodice is not open in front over stays or stomacher; it is likely back-fastening. The sleeves are very short, not longer than the elbow. The neckline is nearly off the shoulders, not up close to the neck. (That point of construction is integral to the mantua.) And the skirt is only draped back slightly, not folded back on itself so the reverse is visible.
So what does that make it? Similar contemporary pictures are of royalty, and/or the most formal of all forms of dress.
Queen Anne, ca. 1700.
Marie Anne de Vaviere, Dauphine, "end grand costume":
"en grand costume"
Get it? The Duchess is in court dress! The robe/train she wears, the flash of ermine on her right shoulder, and the coronet by her left elbow all support that view.
Corsets and Crinolines claims that c. 1690s-1720s court dress retains the earlier fully boned bodice, without stays, that was ordinary in the mid-1600s. That means that the "Majestic Mantua" has far more in common with the opulent gowns of the Charles II court than with the mantua and the sacque. Thankfully, the ladies of the Charles II group on LiveJournal have already done a great deal of the research on this type of garment!
More to come! First, materials, and then how I'm planning to construct this.