Yesterday I showed my third version of Ottobre Woman's Everywoman's Favorite Cardigan from their 5/2009 issue. Oh, you didn't see it?
I've purchased two Ottobre Woman magazines (love them, but I don't feel a need to own every one of their bi-yearly issues) and it seems to me that OW is very fond of using shaped, topstitched facings. Me too! They add nice interest to the design, they make for a very sturdy and neat construction (as opposed to a binding or band) and they eliminate any chance of the facing not staying right where it should at all times.
Ottobre mentions understitching the facing after applying it, but then they don't provide much guidance for topstitching. If the topstitching is to be a simple straight stitch, it's possible to topstitch from the wrong side, using the edge of the facing as your guide. But if you want to use a twin needle, that won't work, since you must stitch with the right side facing up for the two rows of stitching to be visible on the right side. I really want the topstitching to echo the shape of the edge it follows, but since it is two inches away from that edge, it's difficult to make the stitching line smooth by establishing a guide based on the edge.
I like to machine baste the facing in place from the wrong side, using as long a stitch length as possible (5mm in this case) and very slippery thread. Sulky rayon works very well for this. Since I don't machine embroider, I don't begrudge the Sulky for this use.
After the facing is basted, I follow my basting line using the twin needle and matching thread on the right side.
The slippery thread is easy to remove, even from a knit.
Oh, I should mention that I nearly always use the walking foot with the twin needle on knits. Experience has shown that the walking foot vastly reduces or eliminates skipped stitches.
Even though I'm usually no fan of basting, and this method does involve rethreading the machine, it's totally worth it for the quality of the results.