Roxbury, 22 November 1955 - Institutional correspondence Alexander Calder's letter to Willem Sandberg, dated 22 November 1955
Madrid, 4 February 1988 - Internal institutional documents Reply from Spain's Ministry of Culture regarding the questions put forward by Andrés Ollero in the Congress of Deputies
Roxbury, 12 January 1956 - Institutional correspondence Alexander Calder's letter to Willem Sandberg, dated 12 January 1956