TAOS (AP).- A Taos museum is about to open an exhibit by an abstract painter who was a quiet fixture of the local community but who was well-known in the art world for her seemingly simple and muted grid paintings. “Agnes Martin: Before the Grid” opens Feb. 25 at the Harwood Museum of Art in Taos. Martin, who died in 2004 at age 92, would have celebrated her 100th birthday in March. Each of her paintings is a unique exercise in perfect scale and proportion. The show at the Harwood is the first large posthumous exhibit of her work and the only one to highlight such an extensive collection of paintings and drawings that predate the grids that made her famous. It took a small team of curators about two years to unravel the mystery of her artistic beginnings. Playing detective,