The ex-king of Naples' library possesses a Book of Hours, on the illuminations of which (Vasari tells us) Giulio Clovio spent nine years. It certainly is a marvel of human patience and misdirected skill; the text was written by a famous scribe named Monterchi, who was specially renowned for the beauty of his writing.
An interesting little volume on this subject has been published by Eug. Müntz, La Bibliothèque du Vatican, Paris, 1886; it deals chiefly with the growth of the library during the sixteenth century.
Fra Sebastiano was called "del Piombo" from his office as superintendant of the pendant lead seals, piombi or bullae, which were attached to Papal Briefs and other documents, one class of which were called Bulls from their lead bullae.
See Montault, Livres de chœur des églises de Rome, Arras, 1874, p. 9.
The Fitzwilliam Museum possesses two noble vellum choir-books of this class dated 1604 and 1605. Though the miniatures are poor, the writing of the text and the music might well pass for the work of a fifteenth century scribe.