Figuring out how to construct the shoulder straps was more difficult than I expected. I wanted a way to keep them snug against the body yet also allow some flexibility for movement. A simple tube of fabric pressed flat may have worked, but a should strap like that would almost certainly cut into the shoulders or be too loose. I did not want to have them tie like the 1780 stays, that just didn't seem right, and I also didn't want them to be just plain elastic. We'll know how well my solution works when the corset is finished.
I started by making a 1 inch wide tube of brocade, the same width as the elastic I am using. You can see the elastic will just fit inside.
After the seam allowance was pressed open and trimmed I turned the tube right side out and pressed it flat, so the seam allowance now ran down the center. I sewed the end of the elastic to a piece of twill tape, then pulled the twill tape through the tube of brocade.
I pulled the tape until the elastic was inside the tube under the folded under edge. Then I stitched the across the folded opening sewing the elastic and the brocade together. After flipping the strap-to-be over I stitched the length from the front side 1/16 from each side, securing the twill tape inside to the brocade.
I'll attach the elastic end of the strap to the back of the corselet so there will be two inches of elastic exposed and hopefully the strap will function as planned.