You'll have noticed by now that the armholes of the gown's bodice are a very unusual shape to modern eyes: they're positively elliptical, eye-shaped perhaps, and very off-the-shoulder.
In the 1660s the sleeves were attached in an equally unusual fashion. Instead of sewing them on flat around the bottom and gathering around the top as we might do nowadays, most of the sleeve was attached "flat" around the bottom and front of the armhole, leaving all the bulk gathered at the back into cartridge pleats between the top of the shoulder and the back point of the eye shape. This made the sleeves very "poofy" towards the back.
In the painting (right: detail of The Music Lesson, C.1662, Jan Vermeer van Delft) you can see this in action, with all the fullness at the back. It's important to keep this shape as much as possible in order to get the right silhouette, so we'll be emulating this method.
1. I used a different sleeve pattern from the one in your Reconstructing History pattern, but it's a fairly easy one to draw on a large sheet of paper. Draw the grid (below left) first, then draw in the pattern (below right), using the grid as your guide. Since the sleeve is cut so big and then pleated to fit, this is a one-size-fits-all-adults pattern. To complete it, add a seam allowance all round.
Click to enlarge
If you're making the gown for a child, you may need the pattern to be a smaller size. You may guess, for example, that your child is about half adult size - try using the same grid but halving all the measurements. Then use those numbers to draw the pattern.
If you doubt that the sleeve pattern will work for you, I suggest experimenting with a piece of scrap fabric by making a "mock-up" sleeve and adjusting it as necessary.
2. Cut the sleeve out twice in fashion fabric and twice in lining fabric. Don't forget that the sleeves will need to be mirror images of each other! Also, DON'T cut the muslin undersleeve yet.
3. Sew each fashion fabric piece to each piece of lining, right sides together, down the straight edges only. Turn them the right way out and press.
4. Machine baste along the top and bottom edges (ie. sew as normal with your usual seam allowance, but with a long stitch.)
5. Tip: You may find it tough to get the sleeves the right way up (I did too!), so compare them to the pattern carefully and stick a safety pin in the seam allowance to indicate the top. (You could even include a scrap of paper saying "TOP!") Do the same to mark which is the left sleeve and which is the right, also to save frustration later!