The deep burgundy oil on canvas, one of the artist’s color field paintings, is expected to bring $35 million to $50 million at Sotheby’s in New York in May.

The proceeds will also be used to create a new endowment fund for future acquisitions.

Neal Benezra, the museum’s director, said the board last fall established a new strategic plan that “calls upon us to really begin work on diversifying our collection.” With a total acquisition budget of $3 million, Benezra added, the museum depends on donations and cannot compete in the highly escalated art market.

The Rothko has not been exhibited at the museum since 2002 nor lent since 2008, Benezra said, whereas his monumental “No. 14” from that same year remains permanently on view.

Peggy Guggenheim donated Rothko’s “Slow Swirl at the Edge of the Sea” in 1946, where it remained until the museum asked the artist to swap it for a more contemporary example, receiving “Untitled” in exchange.