The drawing is from Janet Arnold, and the picture is not the same dress, but it is the same cut.  Weird, right?  I have no idea which museum it’s in.

From about 1780.

Lauren’s edit: the extant is from Manchester Galleries (c. 1780-90). They seem to actually be the same gown - same color, same pattern (except in J.A., it’s described as “a woven striped design of tiny orange and bright pink crescent shapes” and in Manchester City Galleries, it says “figured with rows of red spots”), same design, same cut, same year span. I don’t know if the “Gallery of English Costume” is the same as Manchester City Galleries (I googled it, and the first to come up was that, but it still wasn’t the exact wording), but the dresses are remarkably alike.

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