The Willem de Kooning blockbuster retrospective at the Museum of Modern Art closed in January, but there is more de Kooning to come for the Modern. While the retrospective was large — about 200 works covering nearly seven decades — it did not include a suite of 24 drawings de Kooning created in 1966, using a Surrealist technique intended to challenge his technical abilities: He made them with his eyes shut. Jan Christiaan Braun, a collector who is a member of the Modern’s drawing committee, bought the drawings from the artist’s estate and has now donated them to the museum. “We have a wonderful collection of de Kooning drawings but we had nothing from 1966,” said Connie Butler, the museum’s chief curator of drawings. “That year was the culmination of his exploration with the figure, particularly using charcoal. Although de Kooning was always thought of as an Abstract Expressionist, I see these drawings as a Conceptual project.” De Kooning described how he held a sketch pad horizontally and drew with charcoal, experimenting with all kinds of challenges: eyes closed; only with his left hand while watching television; with both hands. Ms. Butler said she was planning to show the group sometime next year.