Today I'm going to show an alternate method to elasticize the back of your Winifred dress. Instead of going the elastic in a casting route, you can use elastic thread to create lines of smocking.
It's a super simple method that also gives you some extra visual interest to the back. The smocking will work well with the ties and a buckle, or you can leave them off as I did.
You'll need some elastic thread - I'll be using Gutterman brand, tailors chalk/disappearing ink, an empty bobbin and the back pattern pieces of your Winifred dress. Before adding smocking to your dress you'll need to sew the CB seam, press and finish the edges. On my example I've removed the CB seam by cutting the back on the fold. This works well if you have wide 60" fabric. Just be sure to remove the seam allowance from the pattern before cutting or your collar won't fit.
1. Hand wind your bobbin with the elastic thread, putting a little bit of tension on it as you wind. It won't take too long because the elastic thread has a thicker diameter.
2. Put regular thread in the top of your machine and set the stitch length a little longer than you usually use for seams. I've set my machine to a 3 stitch length.
3. On your back dress, draw a line in chalk or disappearing ink between the two lower waist notches. Mark the beginnings and ends of the lines about 1" away from the edges. This keeps the smocking out of your seam allowances when sewing up the side seams.
5. After completing the first line of stitching, you will use the edge of the presser foot as a guide to stitch the rest of the lines. Each line of smocking will be 1/4" away from the other.
Pull the the fabric flat as you stitch another row to keep a uniform look.
6. Continue stitching the parallel lines of elastic thread until you've stitch up to or a little past the upper waist notch. Once you are done trim the thread ends close to the fabric.
7. Set your iron on a high steam setting like cotton. If you have a steam burst button use that as well. Place the iron next to the smocked fabric, but not on it, and let the steam hit the elastic thread. The steam will make the thread gather in to it's fullest extent.
Give the smocking a few good steam bursts across the entire length of the back and let the fabric cool off. Once it's cool you're ready to move on to the next construction step.