I did a little reading from "Couture The Art of Fine Sewing" by Roberta Carr, looking for answers to my basting questions. I learnt that short, even stitches, in-out-in-out, similar to gathering should not be used for basting or thread tracing (p 44). To thread trace, take a long stitch, then short, then another long. This is to ensure that the fabric remains flat.
Oh dear, I have already done all that thread-tracing with even stitches. I don't think that I will re-do it. This is a learning process and some of my learnings will no doubt benefit my next couture garment! For once, I have not chosen the world's most expensive fabric for a project (though it is still beautiful), knowing that I would be trying out a lot of new techniques.
Onto basting. Baste with a single thread and no knots. On long seams, tie off loosely at the beginning and end to secure basting (p 46). In the purist form of couture, stitching lines are indicated on the right side of fabric. This allow you to fold one seam over the other and slip baste from the right side for maximum accuracy (p 45). So there is my answer...folding and slip-stitching. I have used this technique for princess seams before.
Of course, all that reading just created more questions. Page 47 reveals that dirctional staystiching is rarely used in couture, and never on necklines as so often recommended, nor on armholes. This is in contrast to the Susan Khalje Threads article I am following (Vol 135) which says to hand-staystitch the neck edge, fold under the seam allowance, and catchstitch it to the underlining.I have also been referring to her Master Class article in Threads Vol 125 which says to machine-staystitch the neckline and armhole edges on the seamlines of both the fashion fabric unit and the lining. Several steps later, the pressed edges of the lining are placed slightly inside the fashion edge fabric, and joined to the neckline and armhole edges with small, firm fell stitches right at the line of staystitches. The Roberta Carr book makes no mention (that I can find) of how linings are attached. If I am attaching the linings by hand, I don't see how I can get a smooth neck edge without stay-stitching before turning? I was going to use a walking foot for the stay-stitching. Well, I guess I'll have a lot of time to contemplate this, as I slip-baste all my seams together...