Firecracker and I stopped by a garage sale last weekend. I'd given her 50 cents before we left, so she could choose something. She came home with these:
Of course, what little girl could turn down a red flowy shirt with a heart made out of little bits of shell...never mind that it was a few sizes too big. She wanted to wear it right away, but it kept slipping off a shoulder, so it needed to be fixed...and right away.
It turned out the collar had a fairly wide facing (is that what it's called) on the back of the collar. I snipped a little slit, so I could put elastic through it.
Then I pinned the facing to the shirt with the elastic as close to the seam as possible.
Next, I sewed a casing with the elastic already inside it.
Then I pulled the elastic until it was as gathered as I wanted it to be and sewed short seams to hold the elastic in place.
The finished collar looks like this. I used 1/4 inch elastic. A slightly thinner elastic would have been even better, but this is what I had on hand.