1482–1499 - Milan I—The Sforza Years: Stability and Scale

Where was Leonardo in 1494? He was at the Parish of Saints Nabore and Felix in Milan, recording the burial of a lady named Caterina, almost certainly his mother.

The "Sforza Years" snapshot tracks a period of unprecedented professional scale, where he served Ludovico "Il Moro" Sforza not just as a painter, but as a "General Architect" and master of court spectacles.

Household Accounts and Salai (1482–1499) In 1482, Leonardo moved to Milan, famously offering his services to Ludovico Sforza via a ten-point letter emphasizing his skills as a military engineer. In 1490, a ten-year-old boy named Gian Giacomo Caprotti, whom Leonardo nicknamed "Salaì" (the little devil), entered his household.

Leonardo’s notes on Salaì are among the most intimate records of his daily life, listing the boy's misdemeanors: "a thief, a liar, stubborn, and a glutton". In July 1493, Leonardo notes that "Caterina came to stay," followed by a detailed list of funeral expenses in June 1494 for "Chatarina de Florenzia," who died of malaria at age 60.

Forensic Chemistry of the Last Supper Recent synchrotron X-ray analysis conducted in 2023–2024 has yielded definitive chemical signatures for Leonardo’s Milanese palette. Analysis of the ground layers of "The Last Supper" (c. 1495–1498) revealed the presence of a rare compound, plumbonacrite ($Pb_5(CO_3)_3 O(OH)_2$), alongside shannonite ($Pb_2 OCO_3$).

This confirms that Leonardo was treating his oil with lead (II) oxide (Pb O) to create a thick, fast-drying paint suitable for the humid environment of the refectory at Santa Maria delle Grazie. These findings redefine our understanding of his technical "experimental failure" as a calculated but risky chemical innovation.

The 1499 Route Reconstructed Instructions for follow-up investigative agents: "Reconstruct the exact route Leonardo took from Milan to Venice in late 1499 following the French invasion. Cross-reference the movements of Luca Pacioli and Salaì.

Track the brief sojourn in Mantua and identify the specific rooms in the Castello di San Giorgio where Leonardo produced the portrait of Isabella d'Este. Locate documentary evidence of his consultation with the Venetian Senate regarding the defensive works on the Isonzo river.".

The Sforza Track Geo-Location: Milan. Specific residence: A house near the Porta Vercellina, later receiving a vineyard from Ludovico Sforza in 1499. Primary patron: Ludovico Sforza. The Workbench: Started: "The Virgin of the Rocks" (Paris version, 1483), "Lady with an Ermine" (1489), "The Last Supper" (1495).

Abandoned: The "Gran Cavallo" clay model, destroyed by French archers in 1499. Scientific Breakthroughs: 1490: The "Vitruvian Man" and the beginning of systematic anatomical dissections. 1492: Extensive studies on the flight of birds and aerodynamic principles. World Context (Collision Point): 1499: The invasion of Milan by Louis XII of France.

Leonardo’s world collapses as his patron is overthrown, forcing him into the most itinerant and "action-oriented" phase of his career.