Success! I used the simplest of the stitches I'd tried, a star that was just an outline; an ordinary foot rather than a walking foot; tension on 2 and the Janome FMQ bobbin case. That came out fine on the log cabin strips, and I went on to do random lines of stitches on the background of the quilt. Not sure that I'll be able to take a photo, as the thread blends very well with the background, but when I've dealt with the million and one threads I've got to make disappear, I'll try.