There's a small problem with auditioning border sizes. . . . I don't actually have the floor space to lay the quilt out or a design wall. I used a twin sized quilt as my back (and pinned like crazy) to do square placement, and then I had excess fabric so I went a little over and made it full. The bed photo is a full sized bed and there's just not enough side fabric so it gets a border. I actually feel like its adding something now, but I don't feel like I can get enough of a feel to eyeball it and if there's a way to figure it mathmatically that would be easiest. .
If you don't think that mitering would add to the picture frame feel I could just not do it. I'm planning on machine quilting around the border and hand quilting branches and leaves in a cinnamon brown that matches the border to reinforce the sun dappled feel of the patchwork, so I want the border to feel as much like a frame as possible, and a nice miter does that. I definately don't want cornerstones.
The idea of a thin rust border is interesting. It would mean more fabric shopping, but I could see it adding to the frame. I could even match it to the pearl cotton I'll be quilting with . . . Or use it to comment the blacks in my patchwork fabric with the brown with a burnt umber color. I'm not 100% sure it's necessary. I kind of ditched the multiple border idea when I bought bunches of the leaf fabric, but now I'm revisiting it. Oh dear!