The painting presents two different moments of the Christological story, arranged in a tripartite representation through a monochrome quadratura.
The protagonists of the Annunciation are represented at the extremities: Mary on the left, genuflected on her knee and with her arms crossed at her chest, is caught in the moment of daily prayer in front of the open book. Her attention is distracted by the sudden arrival of the archangel on the right, towards whom the woman turns her eyes.
Gabriel enters the room with his wings outstretched and his rich fluttering damask robes, bringing the Virgin a lily, the symbol of his purity, and the announcement of the Incarnation of the divine Word, which takes the form of the dove of the Holy Spirit, accompanied by the ray of light that radiates into the humble domestic interior from the open window.
The Last Supper
In the central frame, fragmentary, the episode of the Last Supper is recognizable: around a table that has been laid, of which only a portion with a glass and a loaf of bread survives, the apostles are represented with worried expressions and questioning glances, following Christ's announcement of Judas' betrayal. The latter can be identified in the character at the lower edge of the composition, isolated from the group and depicted, as usual, from behind; more problematic is the identification of the other apostles, while the figure of the Redeemer, who was at the center of the scene, has disappeared completely: today it is a large gap in the pictorial surface.
The illusionistic quadratura
To unite in a coherent structure the two episodes of the Annunciation and the Last Supper is a sculptural illusionistic frame decorated with rosettes, herms, scroll friezes and the faces of winged cherubs, inhabited by two full-length angels who, like theatrical curtains, seem to want to introduce the Virgin and the archangel Gabriel in the central episode.
In the center of the stone molding is a fragmentary MDCX [...] date that re-emerged during the most recent restoration: an important chronological handhold that allows the fresco to be dated between 1610 [MDCX] and 1649 [MDCXLIX] and 1690 [MDCXC] and 1699 [MDCXCIX]. Considering the style of painting and that the monastery of S. Caterina was finished by 1627, when the nuns took possession of it, it is possible to conclude that the fresco was painted starting from that year and probably by the first half of the 17th century.