Process

Overview

If Practice is the toolbox, Process is the workflow. How does a painting go from an idea — a commission, an inspiration, a problem — to a finished work? What are the stages? What did Leonardo advise students to do? And what did he actually do himself?

Leonardo's process was legendary, and not always for good reasons. He was famously slow. He accepted commissions and took years (or decades) to deliver. He abandoned works mid-process. He returned to paintings after long gaps. The Mona Lisa may have traveled with him for sixteen years. The Adoration of the Magi was never finished. The Battle of Anghiari was started, experimented upon, and lost.

But his advice to students is remarkably practical: observe first, sketch freely, compose carefully, transfer precisely, paint patiently. And his own process — meticulous planning, iterative revision, and slow, layered execution — was the engine behind the unprecedented realism of his finished works. The gap between Leonardo's advice and Leonardo's practice is itself one of the most interesting things about him.

Observation

The first step. Leonardo insisted that painters must learn from nature, not from copying other painters. Look at the world. Study real faces, real bodies, real landscapes, real light. Carry a notebook everywhere. Draw what you see. His notebooks repeatedly emphasize careful observation of how light disperses and how colors diminish with distance (aerial perspective), guiding artists to modulate tone and hue to achieve depth. The process begins with the eye and the sketchbook.

Sketching and Composition

From observation to invention: the componimento inculto — the "rough composition," a rapid sketch to capture the overall arrangement of a scene. Leonardo advised making many small sketches before committing to a composition. His surviving composition studies show this process — loose, searching, experimental.

The Cartoon

Once the composition is resolved: the full-size drawing (cartoon) used to transfer the design to the painting surface. The Burlington House Cartoon (St. Anne) is a surviving example — a finished, detailed drawing at full scale, ready for transfer. The transfer was done by pricking tiny holes along the outlines and pouncing charcoal dust through them.

Yet even after transferring a drawing onto the panel, Leonardo did not rigidly adhere to it. Infrared reflectography and modern imaging consistently reveal significant changes (pentimenti) under the paint — indicating that Leonardo kept adjusting the composition as he painted. He treated the initial layout as a flexible guide rather than a fixed plan.

Underpainting

After the underdrawing, Leonardo often executed a dead-coloring or underpainting in a monochrome or limited palette. In the unfinished Adoration of the Magi (1481), he blocked in many forms with a warm brown grisaille tone, creating a value structure onto which colors would later be applied. In flesh areas he sometimes used a greenish underlayer (verdaccio), over which rosy flesh glazes would be added to neutralize and create realistic skin tones.

Layered Modeling

Following the underpainting, Leonardo's process involved building up the forms gradually: major shapes first, then increasingly fine modeling, and finally surface details and highlights. Because of his slow-drying glazes, he had to work patiently and out of sequence — often laying aside a work for weeks to let layers cure. Contemporary accounts mention that he would "take years to work through successive layers requiring months to dry."

The Mona Lisa — which he kept with him for years and perhaps never considered truly finished — was the product of dozens of such cycles of layering and waiting, each pass adding more nuance to her expression and the atmospheric background.

The Problem of Finishing

Leonardo's greatest struggle. He saw further than he could paint — or perhaps he saw that finishing meant stopping, and stopping meant settling for imperfection. His unfinished works are among the most revealing things he left us: they show the process frozen mid-step, the scaffolding still visible beneath the art.

Several of Leonardo's major commissions were left incomplete — which, paradoxically, provides modern observers a window into his process. These are case studies of how a Leonardo painting is built.

Saint Jerome in the Wilderness (c. 1480s)

Large areas of the panel remain in underdrawn or underpainted state. The saint's figure is modeled in a monochromatic brown wash, and the background is sketched in with minimal color. We can literally see Leonardo's layering process halted midway: the anatomy of Jerome is fully rendered in light and shade (demonstrating his anatomical knowledge and careful building of form), yet the overlying flesh tones and finer details were never added. The lion at Jerome's feet is only outlined and partially shaded — a ghostly presence that reveals how Leonardo would rough in secondary elements and refine them later.

Adoration of the Magi (c. 1481)

This large panel was abandoned when Leonardo departed Florence for Milan, leaving it in an intermediary state. Cleaning in 2012–2017 removed centuries of darkened varnish and revealed Leonardo's underdrawing and underpainting with unprecedented clarity.

In the cleaned image: fully modeled figures in the foreground (the kneeling Magi and attendant figures have detailed form in brown monotone), while some background elements remain merely sketched. The rearing horses in the central background — previously obscured — emerged as beautifully modeled forms in brown underpaint. The restoration unveiled numerous pentimenti and adjustments: multiple positions of a horse's head, changes in the placement of figures, architectural details like steps and ruins with construction workers sketched in.

Scholars noted that the improved legibility "permits better understanding of the artist's working methods" — we can see how Leonardo layered ideas and pigment alike, building up narrative and forms together. The Adoration stands as "one of the most important testimonies to the artist's working style."

Leonardo wrote extensively about how to train as a painter — a complete curriculum scattered throughout the notebooks:

1. Study geometry — the mathematical foundation
2. Then perspective — how space works on a flat surface
3. Then proportion — the ratios that govern the human figure
4. Copy drawings from a master — learn technique by imitating good work
5. Draw from plaster casts — learn to see three-dimensional form
6. Draw from life — the transition from copy to observation
7. Study anatomy — understand what lies beneath the surface
8. Study light — how illumination creates form
9. Practice every day — the irreducible requirement

His influence on later artists was as much about how to paint as what to paint. His pupils and followers in Milan — Boltraffio, Luini, and others — tried to imitate his sfumato and careful layering, spreading his technical legacy. And his example set a new standard: that a painting is built, not merely painted — constructed with the same meticulous care one might devote to an engineering project or scientific experiment.

Advanced scientific examinations have shed new light on Leonardo's process, often confirming historical accounts while adding precise chemical and structural detail.

Pentimenti Revealed

In 2019–2020, the Louvre released new infrared reflectography images of the Mona Lisa, revealing previously unseen preparatory lines and changes. The position of one of her fingers was shifted, and the transparency of her veil was altered — subtle pentimenti indicating Leonardo refined these details during painting. The National Gallery in London conducted similar studies on their Virgin of the Rocks, finding sketch lines beneath the paint showing a different pose for the Infant Christ, later covered over.

Chemical Fingerprints

The 2023 synchrotron X-ray diffraction discovery of plumbonacrite in the Mona Lisa's ground layer provided the first chemical confirmation that Leonardo incorporated lead oxide into his painting medium — physical proof of his experimental process. The same compound was found in The Last Supper's wall preparation.

Pigment Mapping

Synchrotron X-ray fluorescence (XRF) scanning has allowed scientists to non-invasively "peel back" paint layers of masterpieces. A landmark study on seven Leonardo paintings in the Louvre found that he consistently applied 20 to 40 microns of diluted oil glaze in shadowed flesh tones, with different "recipes" for each painting — some enriched with manganese, others with copper-based glazes.

Authentication

Technical analysis has also helped clarify which parts of Leonardo's paintings are by his hand. The Salvator Mundi attribution examined whether the layering, pigment types, and underdrawing style matched Leonardo's known practice. Certain features — handling of flesh glazes, the presence of lapis lazuli in shadows — were cited as consistent with his repertoire. Thus, technical forensics has become an essential complement to connoisseurship.

Adoration of the Magi (unfinished)

The most revealing process document — underpainting visible, pentimenti abundant, the 2012–2017 cleaning revealed the full architecture of Leonardo's method.

St. Jerome (unfinished)

Shows the monochromatic under-layer before color application — the layering process halted midway.

Burlington House Cartoon

A full-scale cartoon ready for transfer — the composition stage frozen in final form.

The Last Supper

Vasari's account of Leonardo staring at it for hours without painting. The experimental wall technique. The struggle between process ambition and material limitation.

Mona Lisa

Sixteen years of work; the process as the product. Infrared reflectography (2019–2020) revealed finger shifts, veil changes, preparatory lines — a dynamic evolution from initial draft to final image.

Virgin of the Rocks

The National Gallery version: infrared and hyperspectral studies revealed a different initial pose for the Infant Christ, later covered. The Louvre version: XRF mapping quantified the glaze layer structure.