170 Suffolk Street, near Houston Street, Lower East Side Through April 15 Post-Minimalism rarely strays as far from the Minimalist mother lode while adhering to its underlying principles than does the art of Thomas Kovachevich, whose barely there, self-effacing efforts have lately been widely admired by younger dealers and artists. Since the early 1970s, Dr. Kovachevich, a retired physician, has eschewed Minimalism's preference for heavy metals while often embracing its penchant for repeating, literal-minded "one thing after another" compositions. But he has never been averse to letting chance mess with the order of things; in this you could say that he splits the difference between John Cage and Donald Judd with unusual evenness. This is apparent in Dr. Kovachevich's second Lower East Side gallery show this season. The most imposing works are made of nothing but narrow strips of white tissue-thin packing tape, topped by equal lengths of brightly colored grosgrain ribbon, installed vertically to form large, fragile-looking candy-striped rectangles on the wall. They are pinned top and bottom but are otherwise loose. The effect is implicitly pictorial: more early Frank Stella meets Agnes Martin meets Gene Davis than Judd. But the literalness of the pinned-up presentation seems sculptural, as does the way the works change as the humidity rises or falls, and in the process implicates the entire room as a volume. When the air is dry, the tape curls around the ribbons, fogging their colors of pink, orange, yellow or blue and suggesting delicate versions of Dan Flavin's fluorescent tubes. When the humidity rises, the tape relaxes and flattens, revealing the ribbons" hues at full cry. The works amount to an indoor demonstration of an optical condition known as Alpenglow: the intensely colored skies that can occur near mountains because of extremes of humidity and temperature. Here Alpenglow is summoned by means so economically elegant as to be Zen, and with results so visually entrancing as to be beautiful.