When Tom Varner last came to town, in 1996, he had agreed to spend almost a week working with four local strangers to present his own stark and sometimes challenging compositions. That alone would have qualified him as somewhat intrepid–but he’d already earned that description by deciding to play jazz on the French horn. Among the few predecessors and contemporaries he has, Varner stands out for the facility of his technique and the fecundity of his imagination. He makes full use of the instrument’s limited but effective range, which includes explosive rips, nasal, pinched high notes, and a somewhat unmenacing growl, but mostly he relies on his talent for full-blown improvisation, refusing to be limited by his instrument’s traditional role as a symphonic mainstay. His darkly shaded, rhythmically tough music–which belongs to the downtown New York scene along with work by drummer-composer Bobby Previte, the Jazz Passengers, and John Zorn–will again be the focus of his Chicago engagement. The gigs will also reunite the band he co-led last time with bass trumpeter Ryan Shultz; it includes bassist Larry Kohut, drummer Eric Montzka, and altoist Rudy Mahanthappa (who has since moved to New York). When they played together two years ago, these guys jelled pretty quickly into a surefooted but adventurous unit, the frontline horns supplying a burry buzz, each solo seeming to goose the one that came next–and that raises the bar for this installment. Friday, 9 PM, and Saturday, 8 PM, Green Mill, 4802 N. Broadway; 773-878-5552. NEIL TESSER

Art accompanying story in printed newspaper (not available in this archive): Tom Varner photo by Rahav Segev/ uncredited Ryan Shultz photo.