There is some good information here from “apartment therapy” on How to Clean A Quilt, especially vintage quilts which require much more careful handling. The bit about cleaning a wool quilt with snow is very interesting. I wonder, though, how you clean it if you live where you never get snow.
For an old white or light quilt, you also might try laying it on clean grass in the sun to brighten it. I remember reading once that this was an old method for brightening white clothing and it was claimed that it really did work. Of course, you wouldn’t want to do this often with a quilt of any age!
If you have an old quilt that is poorly put together be sure to use extra care in cleaning it. If you have a local quilt shop you may want to contact them to find out if you can get any special help with it or if there is someone locally who specializes in cleaning antique quilts.
One thought that comes to mind is that some wedding dress shops have means and ways for cleaning vintage fabrics because they are sometimes called upon to restore an old dress for a wedding. If you have an old quilt that is velvet or silk or some special fabric you may want to contact local wedding shops to see if you can get some professional help from people who know what they are doing. Ask to see photos or examples of vintage items they have cleaned and restored. However, if they act at all hesitant or like they don’t know what they are talking about, don’t trust them with your quilt (or wedding dress).