When I put a treasured quilt on a bed, I make sure the sheet below has plenty of overlap so that it covers the top edges of the quilt when you sleep. The most dirt comes from direct contact with your body, so to minimize the soil from your arms going out over the top of the quilt the sheet helps a lot. I don't wash my quilts so often when I use that method of keeping them clean in the first place. Some of the old timers basted a really wide strip over the top of their quilts for the same purpose, (about a foot wide).