The Smithsonian and the Getty Research Institute are among the cultural institutions that will soon be able to display a unique archive of images of black Americans in the 20th century.

The four million prints and negatives of the Johnson Publishing Company's archive have been acquired for US$30m (€26.8m, £24.6m) by a consortium of foundations, including the Ford Foundation, the J. Paul Getty Trust, the John D. and Catherine T. MacArthur Foundation and the Andrew W. Mellon Foundation.

Johnson Publishing Company was the publisher of the iconic Ebony and Jet magazines, and the archive features images used in these titles, as well as unpublished works created by staff photographers and freelancers. The photographs depict historically significant moments such as Coretta Scott King at her husband's funeral, and the mutilated body of 14-year-old Emmett Till – the victim of a lynching in 1955 – in his coffin, as well as "slice-of-life" moments and intimate images of artists, celebrities and political activists.

The archive is, according to Darren Walker, president of the Ford Foundation, a "national treasure and one of tremendous importance to the telling of black history in America". He added: "We felt it was imperative to preserve these images, to give them the exposure they deserve and make them readily available to the public."

Lonnie Bunch, founding director of the Smithsonian National Museum of African American History and Culture – where the archive will be displayed – said: "Ebony and Jet magazine helped shape our nation's history, allowing Americans of all colours to see the full panorama of the African American experience.

"Together, our organisations will ensure these images, stories and the history of these publications are well-preserved and available to the public and future generations."