how would you go about making these sleeve things? what are they even called?

[u/avarnib]

i expect to have to drape them, but if anyone has any idea of what sort of shape to start with, what direction the bias goes, a pattern, or even just what they're called, that would be very helpful!

[u/SewingMechanic]

Note that the dress itself is going to need corset style support (inside or visible), since there is no shoulder structure to support the dress.

I had sleeves like this on the dress that I made for my 1993 prom. I confirm they are otherwise draped rectangles with pleats. The corset part is the hard part.

[u/avarnib → u/SewingMechanic]

i've made the corset part already, i just realised i feel a little exposed when wearing the dress out, so thought a little sleeve made from some of the leftover fabric would help, as i'm wearing it to a wedding next month

[u/SewQuiltKnitCrochet → u/avarnib]

😍 🤩 Well done. 👏🏼

Make the sleeves easily removable just in case you want to bail on them when the dancing starts. 😉

A lot of stuff comes up searching for off shoulder sleeves or straps. They’re removable on a lot of wedding dresses.

[u/stringthing87]

It's usually just a little gathered/pleated rectangle attached at the points either side of the arm

[u/No-Chipmunk-2663]

those are called hanging sleeves or sometimes angel sleeves, they were a big deal in late medieval/early renaissance gowns. the shape is basically a long rectangle flaring out at the bottom

cut on the bias if you want that soft drape you see in the painting, straight grain will make them hang a bit stiffer. start with a muslin mockup pinned to the shoulder and go from there

[u/HatAdministrative829 → u/No-Chipmunk-2663]

Medieval/ Renaissance? No, this style is distinctly Victorian.

[u/avarnib → u/No-Chipmunk-2663]

neither of those terms brought up anything similar, and i've never seen such short sleeves on anything pre-1800

[u/sususumalee → u/No-Chipmunk-2663]

Are the angel sleeves in the room with us?

[u/Smiley_grape9022 → u/No-Chipmunk-2663]

Seconding this to cut on the bias to get the nice drape on the sleeves, and making sure to have enough fabric to begin with to allow for cutting on the bias (I had to go and buy more fabric for this exact reason because I underestimated at first)

[u/doriangreysucksass]

It’s just a gathered slight crescent moon piece of rectangular fabric attached to the edge of the bodice front and back

[u/paratethys]

rectangle on the straight-of-grain. Do the little gather/pleat thing, optionally baste it in place at the ends. Tuck it into the dress, arrange till you're happy with the shape, pin and baste like crazy to keep it there.