Central Art Supply Co. was little more than a nook next door to the State Theater until May, when it moved to a 4,000 square-feet space down the road at 1114 Central Ave. Now eight times as large, the store is poised to challenge chain-store rivals like Pearl and Michaels, but it hasn’t strayed from the philosophy that an art supply store should be, in some sense, a work of art. The new space, like its predecessor, features meticulously designed modular shelving and loft-style details like exposed ducts and galvanized aluminum doors. Owner Claudia Strano Jennings, a self-taught artist and furniture designer, made the lime-green resin panels that decorate the bank of cash registers. Supplies are high-end but almost always on sale; working artists with tax I.D. receive a 20 percent discount; students and members of the Arts Center get 10 percent off.