I'll work from the bottom and up on the gown.
- The fabric has a twill weave, the skirt is constructed of square pieces and they used the selvage edge instead of hemming the gown.
- The fabric is cut in a circle, leaving some of the threads running on the bias, and the lighter field is the result of some kind of starch/glue that was used instead of a regular hem.
If we move up from the bottom roundel it's possible to see that when the roundel turns into the skirt part, then the box pleats are spaced closer to each other, I would also think that they are deeper.
The variable pleats are also visible here. Compare the very straight and even pleats under the sash/obi to the ones that are more uneven in order to accomodate the curve of the bust.
The gown ends on top in a quite square neckline, with rounded corners.
The sleeves are almost always hidden under the sleeves of the robe.
So to summarize my analysis of the gown: A lot of the shape in the gown comes from manipulating the width and depth of the box pleats. The gown is lined, but not the whole way to the bottom, since no lining can be seen at the edge of the roundel. The roundel itself is heavily starched. The fabric is probably some kind of twill. I have learnt that there is something called silk twill, and I'm really curious if that might be the fabric that was used.
In the next part I'm going to take a look at the sash/obi.