“Step by Step,” an elegantly mounted exhibition at McKenzie Fine Art, concerns itself with art-making as a form of accretion, a process in which rigorous and often labor-intensive procedures allow for organic expressions of form. Austin Ballard, Ron Janowich, Jim Osman, and Raymond Saá are the featured artists, and it’s a testament to the consistency of the gallery’s curatorial eye that four very individual talents come off like peas in a pod.