The two nationally known artists of “Interstitial Spaces: Julia Barello and Beverly Penn” have several things in common. Both use unusual materials; Barello uses X-ray and MRI films while Penn works with bronze castings. Both create large, elaborate wall installations from small, seemingly fragile forms. Both investigate life cycles and nature. And both explore the empty spaces, or interstices, in their structures. Each woman has several solo pieces in the show at Houston Center for Contemporary Craft, and together they created Submerged, a wonderful wall installation that runs the length of the gallery, made up of free-form shapes cut from X-ray and MRI films and long, delicate seaweed-like plants made from bronze and steel. 10 a.m. to 5 p.m. Tuesdays through Saturdays, noon to 5 p.m. Sundays. Through September 1. 4848 Main. For information, call 713-529-4848 or visit www.crafthouston.org.