The 1740-50 Mantua from Cut of Women's clothes, diagram XIV is not a true mantua, but a mid-century English Gown. Sleeve flounces vs. cuffs date it more toward the 50's than the 40's, though both styles were worn throughout the century to varying degrees.
Cuffs dominated the early part of the century, while flounces were Queen from mid-century on.
The back is cut all in one & pleated to fit. The front has one single pleat each side.
Sleeves are generous, but if you have large upper arms, add a bit to width & height as some of the sleeve becomes the shoulder cap.
The gown should be worn over a small hoop or paniers; basket paniers should not be worn with this gown, though they would be better than nothing. Hip pads or a small rump would also be acceptable.
Bobbi, I've outlined the parts that you will have to finish.
For everyone else, this is a bare sketch of a tutorial & you must have some sewing experience because these are not step-by-step instructions. By no means is this the only way to sew this type of gown & variations in style will demand different steps.
1. Stay stitch all edges
2. Sew backs together, press, stitch seam over or welt
4. Mark pleat lines for front & back with tailor's chalk
5. Sew CB seam together, press. Set aside
6. Sew front darts. Welt seams
7. Back Pleats:
A: lay out back on table & pin pleats in place
B: line up lining & CB seams, pin in place.
C: pin side seams of dress & lining together.
D: carefully fit lining to dress, pinning critical points together (shoulder, sleeve points) & pleat the excess lining so fabric lays flat.
This shows how to ease the lining fabric into pleats (try several different lay-outs to see which works best for your lining).
E: hand stitch lining fabric in place, catching only lining layer.
At this point, set dress on a dummy to check the fit & make sure pleats are laying well.
F: Machine / hand stitch CB seam, side-back pleats of outside through all layers, including lining. DO NOT stitch pleats nearest side seam yet. If you like, you can stay stitch all around the outside, stopping before you get to the side back pleat at the bottom.
G: Set aside.
8. Front lining:
A: sew lacing & boning tabs together with buttonholes or eyelets and a boning channel to help the front lay flat.
B: sew front facing to front lining, turn & topstitch.
C: sew lacing tabs to inside of front lining.
D: stitch lining to fronts from armhole to front-skirt.
E: Set aside.
9. Sew side skirt to side back using French seams or welted seams.
10. Sew side skirt to side front skirt - leaving 9" open for pocket slits. Or place a placket where you want pocket slits to be once you've located them (this will depend on how wide your panels are).
11. Sew side front to side back on bodice. press & welt.
This is what the dress looks like right now...
12. Pleat skirt to bodice & stitch. Pleats should all face toward the side. Mark Center of the slit & skirt, then pleat toward that.
13. Pin outer back pleat to skirt while on dummy over proper undergarments.
This is really important!
Stitch outer back pleat down.
14. Stitch shoulder seam from armhole to neck point (allow pleat to fall free & be set in place later).
This is the dress at this stage.
A: sew side seams of sleeves & linings, press.
B: sew bottom & top edges of sleeves & linings together, right sides out.
C: Sew hem on flounces. Stitch flounces together in place.
D: Gather & stitch flounces onto bands.
E: Sew band onto bottom edge of sleeve. Turn other edge over & stitch that.
Decide if you want a clean edge or topstitching on the outside. This will tell you what side to stitch the band on first & what side to finish last. If you want topstitching showing, stitch to the inside first as seen here. If you want hidden stitches, stitch to the outside first & slip stitch the band on the inside.
F: set sleeve in armhole & stitch in place.
Once you check the fit & position, make a 2nd stitching line on the inside of the first (toward the edge of the seam allowance) to reinforce the seam & tack down the pleats. This helps take pressure off the outer seam & reduces fraying if you toss it in the wash.
Here is the dress at this stage.
16. Front Pleat
A: Pin lacing tabs back. Pin pleats in place (on table or dummy)
B: Starting at bottom front up to sleeve cap, stitch through lining, STOP at sleeve cap (first white dot).
C: Topstitch single layer of fold to end of sleeve cap (red dots). Stop. (White is shown continuing on - DO NOT continue yet).
Note on image: this shows the white arrow going down, go up from CF.
Ironed back facing.
D: Pin back facing in place & adjust front pleats (the unstitched part on the back shoulders) to meet squarely so no raw edges show.
E: Continue stitching through all layers of pleat beyond the sleeve cap.
F: Topstitch back facing through all layers along sides & bottom. Overcast through lining layer only on the inside (you can do this now or when you stitch the front facing).
17. Turn facing over & pin in place on front pleat. Pin carefully. Stitch through bottom layers, do not catch top pleats (IE, your stitching should not show except at the very bottom where there are no pleats). This is best done by hand. Check how it lays on a dummy.
18: set up dummy or have a friend help you pin the hem to length over hoops, paniers, etc. Stitch hem.
19: press all pleats in place.
How to lace the stomacher:
1. lace from bottom to top either cross or spiral.
2. pin stomacher to outside of lining facing.
3: pin front facing to stomacher on inside, weaving pin in & out.
Tabs on the stomacher may be helpful.