"All such type of production on slate and glass, then on semi-precious stones and mirror, forms a major corpus in its own right, utterly different from painting on canvas, wood or fresco, while acheeving a precious quality, even an almost mysterious rarity in some cases; it then ceases at the end of the Baroque style, only occasionally beeing resumed in the XVIII and also XIX centuries".

In 1997, Zeri expresses his views on the subject in these words; they were a head of the times in that field, and feature in an interview with Anna Zanoli for a documentary on the Vittorio Giulini Collection, the most important private one for paintings on stone and glass (Federico Zeri presenta una collezione di dipinti su pietra, 1997, 62').

Zeri's broad overwiev outlines the history and collecting features of painting on stone and glass wich he "links to a kind of love for the unusual, bizzarre, tipycol of the post Renaisance age". He dates their origins from Sebastiano del Piombo lesson and the courtly models for late 16th century roman altarpieces on stone. He examins the spred of such peaces in the venetian and centro-Italian collecting. Not just Italian Schools but also northern masters, holland or germanic area, international Mannerist explore the artistic potential of the oil on alabaster, lapislazuli, djaspro, amethyst, agate, marble, onix, slate.

His notion of works on stone forming a genre a part is mirrored in the Zeri Photo Archive classification in which nearly 500 Photos of paintings on stone and glass are grouped as a separate nucleus, autonomous from the painting sections.
For the most part black and white prints, they were mainly  taken by  the Milanese photograpich studio Perotti in the 1980s and 1990s to document works in the Giulini collection.
Zeri consultancy was fundamental in putting together that collection. He assisted by the youthfull Alberto Protopapa who, a letter in the collection reveals, used to supplie Zerui with photos of the latest acquisitions by the milnaese collector. Zeri's guiding hand was behind protopapa not just in studing or curating the Giulini collection but, as of 1990, in creating a photographic survey aiming to provide sistematic, all-inclusive documentation of painting on stone: the project was rudely interrupted when Protopapa died prematurely in 1993. Comprised of 377 photos fully catalogued and consultable online alongside Zeri's own collection, the Protopapa collection includes a wealth of paper documents providing essential infomation evn on works not documented in photype form.

Taken as a whole, the Zeri and Protopapa collections are highly rapresentative of this output asit has come down to us, especially samll-format works designed forcollects and devotional pourposes. What is missing are the large stone altarpieces produces for roman churches, the photosof wich Zeri included in the Italian painitng section as mentioned in small folder od documentary material within the Protopapa collection.

The painting on glass nucleus documents 69 works largely kept in private collections or having gone at the market. Side by side with works of low technical qualiy, the photos document the extraordinay artistic level attained in this field by the school of  Luca Giordano at Naples with the paintings by Carlo Garofalo that were destined to the King of Spain.  The collection also contains slides illustrating the rare series of Still Lifes on glass signed by Giuseppe Ruoppolo, as well as the finest of 18s works, such as The music lesson, which Zeri expertise attributes to the workshop of Pietro Longhi.

The documentary whose Zeri showes his ideas never went pubblic, beeing designed for the collector's own private ca.... It would nevertheless give a  gi..... outline for the Giulini's collection exhibition that opened at the Milano Palazzo Reale in 2000, Pietra dipinta. Tesori nascosti del 500 e del 600 da una collezione privata milanese, this  sp....ed at a series of international studies that culminated in the recent projects promoted  by the Galleia Borghese in Rome.