Milan, 4 August 1953 - Institutional correspondence A letter from Fernanda Wittgens to Willem Sandberg, dated 4 August 1953
Milan, 12 August 1953 - Institutional correspondence Fernanda Wittgens' letter to Willem Sandberg, dated 12 August 1953
Milan, 7 October 1953 - Institutional correspondence A letter from Fernanda Wittgens to Willem Sandberg, dated 7 October 1953
May - July 1992 - Institutional correspondence Loaned works at the Museo Nacional Centro de Arte Reina Sofía in conjunction with the rearrangement of holdings between the Reina Sofía and Museo Nacional del Prado
Madrid, 8 February 1995 - Internal institutional documents A loan approval form for the exhibition Picasso: The Love and the Anguish. The road to Guernica