Practice

Overview

All the science and all the content in the world don't matter if you can't put paint on a surface. Practice is about the physical reality of making art — the materials, the tools, the techniques, the recipes, the workshop traditions that Leonardo learned from Verrocchio and then reinvented throughout his career.

Leonardo was an experimenter. He didn't always stick to proven techniques — and sometimes it cost him. The Last Supper was painted on dry plaster using an experimental oil-and-white-lead technique (instead of traditional fresco) and began deteriorating within his own lifetime. The Battle of Anghiari may have been ruined by an experimental varnish technique. His willingness to experiment was both his greatest strength and his greatest practical weakness.

But his notes on technique are invaluable. He articulated theoretical principles that directly informed his practical technique: the unity of light and shade, the importance of soft transitions, the challenge to the Quattrocento practice of outlining figures. As he writes: "Of the edges of shadows. Some have misty and ill-defined edges, others distinct ones." This insistence on "insensible" boundaries between light and dark — learned from observing how smoke or haze makes forms blend at a distance — is the theoretical foundation of everything he does with a brush.

Leonardo was trained in Andrea del Verrocchio's workshop, learning traditional egg tempera and fresco methods, but he soon became an innovator in the materials and techniques of painting. By the early 1480s, Leonardo had fully embraced oil painting — then still a relatively new medium in Italy, pioneered in the Netherlands. Oil offered him advantages crucial to his style: slower drying time, allowing extended blending, and the ability to apply paint in translucent layers (glazes).

The Palette

Leonardo's pigments included the brilliant materials of Renaissance painting:

• Lead white — the foundation of all flesh tones and highlights
• Ultramarine blue — from lapis lazuli, fabulously expensive, reserved for sky and the Virgin's robes
• Vermilion red — bright, opaque, mercury-based
• Red lake — transparent, used in glazes for warm shadows
• Yellow and red ochres — earth pigments, stable and versatile
• Verdigris — copper green, brilliant but unstable
• Carbon black and bone black — for the deepest shadows

But it was how he used them that set him apart. Rather than applying these colors opaquely, he frequently mixed them into transparent mediums to create tinted glazes. For flesh areas, he might lay an underpainting of greenish earth (verdaccio — to counterbalance red flesh tones), then apply multiple thin layers of pinkish and brownish glazes on top, resulting in a translucent, lifelike skin effect. Each glaze was modified with slightly different pigment or more medium to modulate warmth and hue.

Lead Oxide and Experimental Priming

Leonardo was an inveterate experimenter with his materials. In the ground layer of the Mona Lisa, researchers found the presence of plumbonacrite, a rare lead carbonate compound — essentially a byproduct of lead(II) oxide (litharge) reacting in oil. A 2023 chemical analysis confirms that Leonardo's base-layer recipe was distinctive: he likely dissolved lead oxide powder in linseed or walnut oil by heating the mixture, creating a thick, honey-like paste that dried faster and formed a firm ground.

Such a medium would suit his slow-working, layered approach perfectly — a stable, fast-drying foundation on which to build his weeks-long glazing cycles. As Carmen Bambach notes, this finding "attests to Leonardo's spirit of constant experimentation as a painter" — using chemistry to achieve artistic ends.

The same compound was later found in samples from The Last Supper's wall preparation, indicating Leonardo used a comparable technique there: oil with lead additive on dry plaster.

Surface Preparation

Leonardo preferred wooden panels (often poplar) primed with a fine white gesso and occasionally an off-white or grey imprimitura (base tone), which provided a stable, smooth ground for his detailed work. The preparation of the surface was itself a craft — the unglamorous foundation that underpins every masterpiece.

Leonardo's sfumato technique (from fumo, meaning "smoke") leveraged the properties of oil to the fullest. He would mix pigments with a high ratio of oil medium and often a resin or drying agent, creating a thin, translucent paint. This was applied in extremely fine layers on the panel, sometimes only 1–2 micrometers thick each, building up subtle tone gradations.

Modern scientific analysis has confirmed just how minuscule and numerous these layers were. In the shadows of paintings like the Mona Lisa and Saint John the Baptist, Leonardo applied 30–40 micrometers total of tinted glaze, accomplished through perhaps dozens of ultra-thin coats that are "rich in organic medium with low pigment content." Each layer contributed a slight shift in tone, and together they produced the hallmark gentle transitions from light to dark — no visible boundaries, just as Leonardo prescribed.

A 1–2 micron glaze is about 1/50th the thickness of a human hair.

The Fingerprint Technique

Leonardo likely blended these glazes not just with delicate brushwork but also with his own fingers. Contemporary accounts by Giorgio Vasari suggest that Leonardo would often smooth and diffuse wet paint with his fingertips, literally feeling the form as he painted. This tactile technique would explain the imperceptible gradations in works like the Mona Lisa's cheeks — effects difficult to achieve with a brush alone.

The use of fingers for blending has been borne out by forensic evidence: a fingerprint was detected in the paint surface of the Lady with an Ermine, and numerous scholars note that Leonardo's soft finish in flesh tones could result from gentle finger smudging.

Layer Recipes

A landmark 2010 study used synchrotron X-ray fluorescence (XRF) on seven Leonardo paintings in the Louvre, quantifying layer thickness and composition. Different paintings showed different glaze "recipes" — some enriched with manganese (from umber), others with copper-based glazes — suggesting Leonardo tweaked his mixtures for each desired effect. This correlates with historical anecdotes that he was continually searching for the perfect shadow mixture.

Lead White Control

In The Virgin and Child with St. Anne (Louvre), a 2020 study using photoluminescence mapping found that the sky was built with two distinct lead white layers — the crystalline forms differed (one more cerussite, one more hydrocerussite). This suggests Leonardo may have deliberately used two grades of lead white: a coarser, faster-drying one below and a smoother, luminescent one on top. The study concluded that "Leonardo… had knowledge and control over pigment scattering properties" — meaning he understood how different particle sizes would affect the look of the paint.

The Last Supper — The Experiment That Failed

The prime example of Leonardo's practical boldness — and its consequences. Unwilling to work within the fast-drying constraints of true fresco, Leonardo devised a new process: he prepared the refectory wall with a double layer of drying oils and white lead priming, essentially trying to turn the wall into an "oil painting" surface.

This allowed him to paint slowly and make revisions, achieving remarkable psychological depth and chiaroscuro akin to a panel painting. Technically, however, the experiment failed: "because the pigments did not chemically bond with wet plaster, the paint layer was fragile from the moment it dried."

The Last Supper's rapid deterioration — noticed within decades — is a direct consequence of Leonardo's quest for artistic effect. He traded permanence for the freedom to layer and blend on the wall. The long restoration (1978–1999) used microscopic and chemical analysis to differentiate original paint from later overpaint, finding that only about 20% of the surface retained Leonardo's original paint.

Drawing Materials

Silverpoint, chalk (red and black), pen and ink, charcoal. Leonardo used different drawing materials for different purposes: silverpoint for precise studies (the medium doesn't erase), chalk for soft tonal studies, pen and ink for rapid sketches and detailed diagrams. His choice of medium was always deliberate — matched to the purpose of the drawing.

Mona Lisa (1503–1519)

The supreme demonstration of sfumato practice. Leonardo applied countless thin oil glazes, particularly in the corners of the eyes and around the mouth, to blur contours and create lifelike softness. Under magnification and X-ray analysis, these areas show multiple layers of semi-transparent paint with finely ground pigments, yielding the smoky modeling of her enigmatic expression. The 2023 plumbonacrite finding confirms that even the primer was engineered.

Lady with an Ermine

Forensic evidence of finger-blending: a fingerprint was detected in the paint surface, confirming the tactile technique described by Vasari.

The Last Supper (1490s)

Experimental dry-wall technique — remarkable psychology and chiaroscuro achieved at the cost of durability. Only ~20% original paint survives.

Virgin of the Rocks & La Belle Ferronnière

Subjects of the landmark XRF scanning study that quantified Leonardo's glaze layers and pigment compositions across multiple works.

The Virgin and Child with St. Anne

The 2020 photoluminescence study revealed two different grades of lead white — evidence that Leonardo controlled pigment particle size for optical effect.

Adoration of the Magi (unfinished)

Reveals the underpainting stage: warm brown grisaille, verdaccio under-layers, the value structure before color. Cleaning in 2012–2017 removed centuries of darkened varnish and revealed the underdrawing with unprecedented clarity.

St. Jerome (unfinished)

Shows the monochromatic brown wash stage — the saint's anatomy fully rendered in light and shade, yet the overlying flesh tones and finer details 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.