Fraying
 

I've recently made a quilt top in the 'Square dance' pattern. There are close to a million tiny pieces, and I'm very proud of it. Here's my problem: I've decided to make it into a duvet cover by sewing a sheet onto the back of it, like a very large pillow case. The pieces all have 1/4 inch seams, and I fear it would ravel in the wash. Is there a product that I could spray onto the back, or iron onto the back, that wouldn't make it too stiff yet would make it less likely to ravel? I would, of course launder it right side out.
The reason I wanted to turn it into a duvet cover was to avoid quilting it. The pinwheels are about 3 inches and the 4 arms of the pinwheels are about 1/2" x 1" and about 1 1/2 inches long. In order to make the pinwheels 'pop' I would have to quilt around the outside of each and every pinwheel, and that's more than I think I'm capable of. I thought that if I could 'glue' a sheet to the underside of the top I could avoid having to quilt it.

That's a whole lot of work not to finish it. I think I'd rather save up and have it longarm quilted than do something like that to it.

you can purchase a fusable interfacing- press that to the back (it is what is used in collars/cuffs of nice shirts=ect. it stays in - there are different weights-choose a lightweight one- it has fusable on one side- the other side is a lightweight fabric-a little like a dryer sheet-but different-
it stays soft- and would protect your seams without really adding weight or bulk. visit joannes-or a store like that and ask for a fusable (stay in) interfacing- they will know what you need

I agree with ckcowl that a lightweight fusible interfacing would be a good bet. There are some that have a tricot fabric - like a light knit, that stay flexible when applied.
I'd also suggest adding another layer of sheet. So that the quilt top and one sheet make one closed pocket, and then the extra layer of sheet makes the duvet pocket. This will reduce the friction between the duvet and the back of the quilt top.