There are occassions when you want to create a really neat join between two seamed pieces, especially when this join is at the top of the piece and so very visible. Within my patterns this occurs at the top edges of both the removable shoes (soon to be released) and some of the designs in my 'bags, backpacks and baskets' pattern.
Above is a picture of the top seam that you're aiming to achieve:
And here's a little tutorial on how to work it...
Normally when you cast off you cut the work from the ball and thread this tail through the final stitch on the needle in order to secure the cast off row and prevent it from unravelling. But that creates a little nubbin at the end of the row and can interfere with a neat join when you start to sew an attaching seam.
So instead, when you have your last stitch at the end of your cast off row, cut the work from the ball and pull on the loop of this last stitch, like so:
Keep pulling that loop until the cut tail is pulled all the way through, effectively unravelling half of this final stitch:
Then thread a tapestry needle with this cast off tail end and sew through both arms of the edgemost stitch on the opposite side of the seam:
Then sew back across the gap and down through the stitch that the tail end is emerging from:
In doing this you have replicated a cast off edge stitch to span the top of the seam between the two pieces (see image at the top)
And then you can continue seaming the two pieces together using mattress stitch ( Mattress stitch seaming tutorial can be found here)
I hope this helps you to get neat and attractive edges to the seams at the top of your removable shoes and bags, happy seaming :)
J x