Portrait of Francesco Maria del Monte
Ottavio Leoni (1578–1630)
The strong bond of affection between Don Antonio and Cardinal Del Monte is clear from their extensive correspondence and gifts to each other. In addition to their passion for alchemy, the two shared a strong interest in glassmaking technology. There is a chance that the cardinal met glassmaker Antonio Neri in Florence; in 1602 he visited the Casino di San Marco, where the glass foundry was located and he returned in 1608, although by then Neri was in Antwerp. Del Monte's biographer Zygmunt Waźbiński offers, "It is very likely that Cardinal Del Monte, with his interest in glass, had known then (in 1598) the [future] author [Neri] of L'Arte Vetraria." 
Del Monte collaborated with Niccolò Sisti, the grand duke's glass foundry master at Pisa, where Neri also worked for a time. Sisti often provided Del Monte with glassware for Medici customers within the College of Cardinals in Rome. The cardinal's patronage also brought many glassmakers in Rome to the appreciation of the papal court. After his death, Del Monte's will shows that at his main residence, the Palazzo Madama, he maintained an entire room, "gabinetto dei vetri" [cabinet of glasswork] that housed five hundred pieces of glassware. It cannot go without mention that he was also the proud owner of what has become one of most celebrated pieces of ancient glass, now referred to as the Portland Vase.
There are indications in Neri's 1600 manuscript that he visited Rome. If so, it is hard to imagine him not seeking an audience with the cardinal, either at his villa on the Pincio, overlooking the city or at the Palazzo Madama, now offices of the Italian Senate. The palazzo was appointed in fabulous luxury and arranged to accommodate a constant flow of dignitaries from around the world. The villa, on the other hand, was where the cardinal's alchemy laboratory was located. This was a more secluded retreat where the cardinal could entertain guests with more discretion.
|Michelangelo Caravaggio, c. 1597|
According to Gian Pietro Bellori, the early biographer of artists, Caravaggio executed the oil painting sometime between 1597 and 1600.  Depicted in the mural are the three brothers Jupiter, Neptune and Pluto: the masters of the universe. The image is a double allegory of the three basic chemical substances of Paracelsus (salt sulfur and mercury) and the four Aristotelian elements (air, earth, water and fire). Jupiter with the eagle stands for sulfur and air, Neptune with the seahorse stands for mercury and water and Pluto with the three-headed dog Cerberus stands for salt and earth. Jupiter is reaching out to move the central celestial sphere in which the sun (fire) revolves around the earth. 
The villa was a relatively secluded retreat where the Cardinal could entertain guests discretely, including his friend Galileo–Del Monte and his older brother Guidobaldo helped land Galileo the chair of mathematics at the university in Pisa. This is also where Galileo demonstrated his telescope for interested dignitaries in Rome. It would be interesting to hear the astronomer’s comments on Caravaggio's tribute to heliocentrism.
 Neri 1612.
 Bellori 1672, pp. 197-216.
 Wallach 1975, pp. 101-112.
*The material in this post first appeared in a different form on 27 Nov. 2013 and 4 Jul. 2014.