The Studio Art Quilt Associates defines an art quilt as "a contemporary artwork exploring and expressing aesthetic concerns common to the whole range of visual arts, while retaining, through materials or technique, a clear relationship to the folk quilt from which it descends." In other words, not surprisingly, an art quilt is an artwork that is a quilt.
The primary distinction between an art quilt and a craft quilt is originality. Because art is a kind of research into how we see and what we find beautiful, an art quilt should offer something new and original to the artist.
Obviously, what makes an art quilt good is a much bigger subject. But there is at least one absolute requirement that I believe in. An art quilt should exploit the strengths of its medium, rather than trying to imitate some other medium. As John Ruskin wrote, "Whatever the material you choose to work with, your art is base if it does not bring out the distinctive qualities of that material....If you don't want the qualities of the substance you use, you ought to use some other substance."
To me, the strengths of the quilt medium are:
A good quilt is very different but equally striking from far away and close up--from far away, because of the strong design and color; from close up, because of the interplay of pattern and texture with the overall design.
Even though antique quilts were discovered as fine art in the 1970s, it is rare to see contemporary art quilts exhibited with artworks in more established media. Most often they are exhibited with craft quilts in quilt shows, or in special shows for art quilts only.
In her remarkable essay on the subject, Catherine Jones attributes this in part to the notion that some common characteristics of quilts, such as cheerful colors and careful craftsmanship, are more acceptable to the established art world when they come from exotic, primitive outsiders than when they come from well-educated contemporaries.
I particularly like Jones's point that clothing a family and decorating a home are aesthetically formative experiences of a majority of women and a minority of men. These visual experiences are under-represented in fine art, and it would be wonderful if quilters (most of whom are women) could bring them into the mainstream.