Later in his career, Hammons has explored the sculptural medium in creating pieces. In his 1970's "Spade" series included works such as "Bird" (1973) where the jazz musician Charlie Parker is evoked by a spade emerging from the mouthpiece of a saxophone. The name of the piece reflecting Parker's nickname of "Yardbird" or "Bird". Similarly, there is "Spade with Chains" (1973), where the artist employs the provocative, derogatory term, coupled with the literal gardening instrument, in order to make a visual pun between the blade of a shovel and an African mask, and a contemporary statement about the issues of bondage and resistance. In his seminal piece, "African-American Flag" Hammons tackles the topic head-on. The piece depicts the American Flag in the Garvey Colours of Black, Red and Green (Pan-African Colours), these colours also being used in the UNIA Flag. The importance of this piece is demonstrated in its status as part of the permanent collection of the Museum of Modern Art in New York. A copy of the flag is hoisted at the entrance of the Studio Museum in Harlem.