Bibliothèque nationale de France, Département des manuscrits, Français 5227, fol. 3v.
Marilyn Perry provides a description and the historical interpretation for this device or impresa of Pope Clement VII in her article: “‘Candor Illaesvs’: the ‘Impresa’ of Clement VII and other Medici Devices in the Vatican Stanze,” The Burlington Magazine, 119, no. 895 (1977): 676-687
CANDOR ILLAESVS–Whiteness undamaged, innocence unharmed–is the motto inscribed on the white banner which curls around a tree and a trunk supporting a crystal ball in the pope’s impresa. Rays of the full sun, shown passing the crystal, are concentrated on two points: one hits the tree, which bursts into flame, while the second, lighting upon the white ribbon, produces no effect. … the device is explained for us by Paolo Giovio who, after a lifetime in Medici service, wrote as an apologist for the pope’s memory in his book on ‘the mottoes, and designs of arms and of love which are commonly called Imprese‘. The CANDOR ILLAESUS emblem, Giovio reports, was invented by Clement’s treasurer, the Florentine Domenico Buoninsegni, a man who ‘willingly fancied about the secrets of nature. He discovered that the rays of the Sun, passing by a ball of crystal, so intensify and unify according to the nature of perspective, that they burn all objects except the very whitest. Pop Clement, wishing to demonstrate to the world that the innocence [candore] of his soul was offended neither by slanderers nor by force, used this impresa during the time of Hadrian VI when his enemies plotted against his life…’ While not without inherent flaws, as we shall see, the emblem was deserving of particular praise in Giovio’s opinion for its elegance.
(For complete notes and annotations as well as extended interpretations, please refer to Ms. Perry’s article.)