I have finished the silk warp today and am happy with the results. When I was measuring out the warp it made sense to me to make the warp long enough for two scarves, one commissioned and one made on spec since the work of warping is not a lot more for a longer warp... within reason.
I knew that making the warp that long was potentially dangerous but decided to risk it. The danger was increased with the change I made after cutting off the first 9" after recognizing that I had omitted four threads in one of the stripes. See "Good news and less good news" of a few days ago. The change I made after re-threading most of the scarf was to contrast the warp-faced twill stripes with a plain weave ground in place of the 2/2 twill ground. It was worth the gamble with a 2/2 ground but once that ground turned to plain weave all bets were off.
For the non-weavers among you, the area woven plain weave is used up faster because the warp threads go over-and-under-and -over-and- under. The twill stripes are over-over-over-and-under. the more times a warp thread (the long way threads) intersects the plane of the cloth, the more it is shortened. For plain weave, that happens with every pick but with the twill, every third pick (or pass of the shuttle). The plain weave threads grow progressively shorter and the others tned to sag.
After a time it was clear that this silk isn't as elastic as I had hoped and sagging was becoming a problem. The twill stripes are double-faced twill--so that both sides of the cloth look just the same--and are threaded on eight shafts. I had threaded the ground on four shafts (because it was a 2/2twill initially) so the stripes were threaded on 5--12. To take up the slack I lifted 6, 8, 10, and 12 and put a very smooth dowel-like stick behind the shafts and then lifted 5, 7, 9, and 11 and put in another stick. I repeated the even-numbered lift and inserted another stick which took up the slack very nicely. I used rubber bands--aka The Weaver's Friends--to connect them at their ends and pushed them back toward the warp beam so that they wouldn't interfere with the working of the loom. Of course, every time I advanced the warp, they had to be moved back but that wasn't difficult.
Once I had finished the scarf, I took the sticks out and made the same sheds and put the sticks in at the front of the loom where they worked as spacers to reserve unwoven warp for the fringes. I wove two scarves and still had about 20" left (I was right about the length of the warp) so I put in sticks again before I wove the 20" at the end. It is enough for a very elegant, white-on-white evening bag. I have some white silk charmeuse I bought from Dharma Trading Company (http://www.dharmatrading.com/) that I will use to line it once I have found the proper interfacing. I might even paint the silk or dye it so that the lining will be a nice surprise....
It may be that weavers are not the most inventive people in the world, but I'd be willing to bet that we are right up there with the best of them.
So, there you have it, a nasty problem and an elegant solution. Score one for the weavers!