I use the Flynn method with the diagonally pieced back when I am using only one material for the backing. It really looks nice.
When I use different materials I just do a pieceworked backing. I just play around with various rectangles and squares and such til I like what I see. I have used graph paper or EQ6 very rarely as it just seems to flow and work.
Quilt and fabric designer Carrie Nelson of Miss Rosie's Quilt Co. pieces many of her backs and usually has an area with a printed verse or such strategically placed on the back. Her backs are as beautiful as her quilt tops!
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