The rich stucco decoration of the vault frames the frescoes created by Dosso Dossi in 1532. In the centre are putti as seen from below; on the sides, the four cardinal virtues (Justice, Fortitude, Prudence and Temperance), and the coats of arms of Charles V and Pope Clement VII de’ Medici. Much lower are two stuccoed coats of arms belonging to Bernardo Cles as bishop and as cardinal.
The seven liberal arts are frescoed in the lunettes, each discipline portrayed by persons from ancient times. The black marble fireplace, from which the room gets its name, was made in 1927 to replace the 16th century original that was lost.