The Portrait of a Musician is the only Leonardo panel painting left in Milan. Traditionally it was thought that it portrayed Ludovico il Moro, Duke of Milan, but when the restorations of 1905 eliminated the repainting and made the hand with the musical scroll re-emerge in the lower part, we began to talk about the portrait of a Musician, now identified with Franchino Gaffurio ( chapel master of the Milan Cathedral), now with the Franco-Flemish cantor Josquin des Prez, both present at the Moro court. More recently, the hypothesis has been advanced that it is Atalante Migliorotti, a Tuscan musician and friend of Leonardo, who came with him to Milan as a singer and skilled lyre player.

This splendid tondo by Sandro Botticelli, executed with a brush tip with a miniaturistic attention, proposes an apparently conventional religious theme (the Madonna and Child), but in reality full of symbolism. Already the same tent, or "pavilion", is one of the most important biblical symbols both in the Old Testament (the "tent of the meeting" as a place of the presence of God), and in the New Testament (in the Gospel of John, to summarize the mystery of the Incarnation, we read: "And the Word became flesh and" pitched his tent "among us"). The two angels who open the "curtain" thus reveal the mystery of the Incarnation: the Son of God who became a child and was born of the Virgin Mother.

Surely this drawing is among the most precious works of the collection and of the city of Milan. It is the largest Renaissance cartoon that has survived and was executed by Raffaello Sanzio, as a preparation for the fresco in the Stanza della Segnatura in the Vatican, which was painted by Julius II. It became part of Federico Borromeo's collection in 1626, when he bought it from the widow of Fabio Borromeo Visconti for the huge sum of six hundred imperial lire, even though it was actually placed on loan at the Ambrosiana as early as 1610. known as the School of Athens, the most exact title would be La Filosofia, as suggested by the allegory of the same name painted in the sail above the fresco in the Stanza della Segnatura, according to a very complex iconographic project. Recognizable, in the center, are the two greatest philosophers Plato (painted with the likeness of Leonardo, with the finger pointing upwards and recognizable because he is holding the Timaeus, one of his works that greatly influenced subsequent philosophy) and Aristotle, identifiable by book of ethics.

This beautiful painting was considered by Federico Borromeo "one of the dearest things I have" and it has been hypothesized that he kept it in his studio in the archbishop's palace, so much so that it became part of the Ambrosian collection only on his death. There have been long discussions on the authorship of the work, but recently it has been stated that "the definition of an autograph replica for the Milanese example is the most suitable". An identical painting, probably the original version seen by Federico Borromeo, is kept in the Prado Museum in Madrid and was donated in 1605 to the Queen of Spain Margaret of Austria by Francesco Maria Della Rovere, Duke of Urbino. From the iconographic point of view, it is interesting to note that the painting totally lacks any source of natural or artificial light, since everything is flooded by the divine light that radiates from the face of the Child Jesus, as indeed narrated in one of the apocryphal gospels.

It is probably the most famous work in the collection of Cardinal Federico Borromeo and is rightly considered a kind of prototype of the "still life". It represents a wicker basket from which fruit and leaves overflow. Many interpretations have been given of it: undoubtedly the extreme realism and the progressively drying leaves make the inexorable flow of time perceptible.

It is undoubtedly the most impressive of the four paintings, the one where the artist's imagination has found greater possibilities of expression. The element of fire is first mentioned in the huge fire. The painter, however, wanted to develop the theme of fire also through the representation of a huge workshop. To produce objects it is necessary to use the force of fire, this time no longer indomitable and destructive, but tamed by the man in the furnace.