On September 25, 1975, the Vatican issued a set of three stamps to commemorate the fifth centenary of the foundation of the Vatican Apostolic Library, which has housed the collection of manuscripts and printed books owned by the Vatican since the fifteenth century.
The 100-lire stamp features a portrait of Sixtus IV, and its source is the Latin Codex 2044. A dark green ink printed the image on a pale green background. Alceo Quieti designed and engraved the stamp.
1,550,000 stamps were issued in panes of forty. They are perforated 13 1/4 x 14. IPS, Rome, printed the stamps using the offset process in two colors and chalcography on white glossy paper.
Reference:
"5th Centenary of the Foundation of the Vatican Apostolic Library." Vatican Notes 24, no. 3 (October-November 1975): 2.