Sometimes an art market “moment” emerges purely by accident; more often it’s a product of foresight and careful planning. Right now, the market for works by Helen Frankenthaler, who died in 2011, seems to be at the beginning of a moment of its own. Over the last three months, the Museum of Modern Art had five of its large Frankenthaler works on display in the museum’s soaring atrium. In mid-April, the Kunstmuseum Basel will open the largest European Frankenthaler exhibition to date, titled simply, Helen Frankenthaler. But both shows are just stepping stones to a major traveling centenary retrospective scheduled for 2028, organized by the curator Harry Cooper at the National Gallery in Washington, D.C.