This recently discovered, monumental sheet is a superb example of the draftsmanship of one of the great exponents of Mannerism in Italy. It relates to one of Salviati's most important fresco cycles, that in the private chapel, or Cappella del Pallio, of Cardinal Alessandro Farnese (the grandson of Pope Paul III) in the Palazzo della Cancelleria, Rome. The artist executed the preparatory drawings for the project in the winter of 1548–49 and finished the frescoes before May 1549. The drawing served as a cartoon (full-scale drawing) for the figure of Saint John the Evangelist on the underside of the main arch at the altar of the chapel.

In modeling the figure, the artist rubbed in most of the individual strokes of the chalks to obtain smoky, seamlessly unified tones and a beautiful marmoreal luster. John is seen in the company of his best-known attribute, the eagle, at lower left, but also holds a chalice with a snake. The latter alludes to the priest of the Temple of Diana of Ephesus, who offered John a poisoned chalice to drink as a test of his faith. Miraculously unharmed, John later resurrected two prisoners who had previously died from the same poison.