candidate: The 31 artists in the exhibition included Walter Darby Bannard , Jack Bush , Gene Davis , Thomas Downing , Friedel Dzubas , Paul Feeley , Sam Francis , Helen Frankenthaler , Sam Gilliam , Al Held , Ellsworth Kelly , Nicholas Krushenick , Alexander Liberman , Morris Louis , Arthur Fortescue McKay , Howard Mehring , Kenneth Noland , Jules Olitski , Ray Parker , David Simpson , Albert Stadler , Frank Stella , Mason Wells , Emerson Woelffer , and a number of other American and Canadian artists who were becoming well known in the 1960s .