The 37 molds made out of painted plaster, which belong to the Vatican Museums, were created during the 1930s and 1940s as a result of the restoration construction sites carried out during the pontiﬁcate of Pius XI (1922-1939). The latter occurred within the two grand monuments of Ancient Christian Rome. Along with these 37 molds, one must keep in mind that there are approximately another 60, among which there are unpainted and mother molds that recently have re-emerged from museum deposits. These will then undergo speciﬁc restoration interventions.
These works marked the beginning of a new approach to the mosaics, given modern orientation and technical experimentation. Now, the mosaic is not considered the only means for the representation of two-dimensional images.
In fact, the molds, as testimonies of the three-dimensionality of the original artifacts, allow us to acknowledge their innovative technical aspects, while documenting their preservation status prior to the discussed modern integrations. The majority of the mosaic molds that, to this day, are preserved in the Vatican Museums, all originally come from the church of St. Mary Major. That is to say, both from the mosaic cycle of Sixtus III (432-440), and from the medieval decorations of the apse and front; the ﬁrst made by Jacopo Torriti and the second by Filippo Rusuti. Likewise, the molds from the mosaics of the lobby of Sixtus III and from the decorations of the chapel of San Venanzio, created by the Popes John IV (640-642) and Teodoro (642-648) for the safekeeping of the remains of the holy martyrs of Salona, were designed for the Lateran Baptistery. Other interesting reproductions made out of plaster involve technical details on the walls pertaining to the two ancient buildings, which were highlighted during restorations.
Today, after 80 years on display, the historical, educational and aesthetic value of these singular documents ﬁnds a new purpose in a recent staging. This staging takes place in the Pius Christian Museum that houses the collection of Christian Antiquities of the Vatican Museums. In addition, this is a very important research project for the studying, preserving, and promoting of these precious artifacts. This major project, links together the Vatican Museums, the Mosaics Museum of Ravenna (TAMO) and the Papal Basilica of St. Mary Major.