Yesterday I made the petticoat and set the sleeves on the riding habit jacket.

The petticoat is worn over panniers. I don't have very big ones, but I wanted to try the drawstring sides method seen on this petticoat from the Met:
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Robe à la Française, detail - 1760-70, French - the MET
The idea is that the length and fullness of the petticoat can be adjusted over the panniers, and you should be able to wear this type of petticoat over different size panniers, or no panniers at all.

I made the petticoat the same way as usual, with the sides open, but I left about 10 inches free on front and back, each side, and stitched in a drawstring. The waistbands stop short of the gathered lengths, so they form a hole on each side.

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American Duchess Historic Shoes Blog

American Duchess Historic Shoes Blog

It seems to have done the trick - hem looks level, yay!

Next it was time to get set the sleeves in the jacket, and, of course, I ran into problems. The sleeve heads were 19.5 inches around, and the armscyes considerably less. I wanted a smooth cap, so I took off the armscye through the underarm and the back, then eased the sleeve head ever so slightly with a gathering stitch. Mission accomplished there, but I'm going to reduce the sleeve head on the pattern before I sew with it again.
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Now the whole ensemble is wearable, but it needs the trim (the best part!). It's certainly not perfect - my velveteen fabric was difficult to work with, and I can see this pattern working much better in wool - but I'm decently pleased with it, so far. :-)
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