Happily, *this* sashing fabric choice made the cut (uh .. oh, a pun!). The ribbon stripes have been removed, pressed and put away for some other project, yet to be determined.
The *REAL* sashing is now being sewn to all those hundreds and thousands and inkle-dillion diamonds. (Not really, but it sure feels like a gazillion.) The setting triangles for each diagonal row are cut out (since I hadn't done them previously), I stack all the diamonds for the row on top of each other then chain stitch them to a sashing strip. They look rather like a banner. :-) The seam allowance is pressed towards the sashing strip and they are then cut apart and re-stacked on each other.
Then the diamonds (which now have a sashing segment sewn to them) are sewn together to form the diagonal row.
The seam allowance is pressed towards the sashing.
A new, long sashing strip is cut and sewn to the newly sewn diagonal row. I have reached the point where a single WOF cut from the sashing fabric isn't sufficiently long enough for the diagonal row. I need to piece the sashing. The seamline should (ideally) align with the sashing segment seamlines for visual continuity. My first attempt (the green dashed line) was almost good enough. I think next time I'll try Sharon Schamber's glue basting tip.
Continue onwards, ad infinitum. This sashing fabric looks very much like the original sashing fabric (of which I didn't have enough), so DD#2 is pleased. I'm pleased that she is pleased. We are both pleased with each other. Isn't that nice? :-)