Leonardo Da Vinci, detail of Compositional Sketches for the Virgin Adoring the Christ Child (recto), 1480–85. Credit: The Metropolitan Museum of Art, New York, Rogers Fund, 1917 (17.142.1)
A study by the Metropolitan Museum uses non-invasive technology to uncover the hidden materials and techniques in six Renaissance drawings, revealing new details about the masters’ creative process.
A team of researchers from the Metropolitan Museum of Art in New York has managed to look inside six extremely valuable Renaissance drawings by Raphael, **[Leonardo da Vinci](https://www.labrujulaverde.com/en…
Leonardo Da Vinci, detail of Compositional Sketches for the Virgin Adoring the Christ Child (recto), 1480–85. Credit: The Metropolitan Museum of Art, New York, Rogers Fund, 1917 (17.142.1)
A study by the Metropolitan Museum uses non-invasive technology to uncover the hidden materials and techniques in six Renaissance drawings, revealing new details about the masters’ creative process.
A team of researchers from the Metropolitan Museum of Art in New York has managed to look inside six extremely valuable Renaissance drawings by Raphael, Leonardo da Vinci, and Perugino. The study, whose results are now being published, employed an array of non-invasive analytical techniques to reveal material details and execution methods that had remained invisible to the human eye for more than five hundred years.
Until now, the artistic media used in these works had only been assessed through visual examination. This study demonstrates how non-invasive scientific methods can uncover aspects of artistic production that would otherwise remain invisible, enriching both the technical understanding and the historical interpretation of art, the article states.
The research focuses on four drawings by Raphael, one by Leonardo, and one by Perugino, analyzing everything from the preparation of the paper surface to the complex layers of red chalk, metalpoint, and iron-gall inks. The work was motivated by the upcoming exhibition Raphael: Sublime Poetry, which will take place at the Metropolitan Museum in the spring of 2026.
Raphael, Madonna and Child (recto) Nude Male (verso), ca. 1506-07.a Visible light image (recto). b Visible light image (verso). c Combined Fe (orange) and Pb (white) distribution maps. d Pb (white) distribution map showing the use of Pb metalpoint in the male figure. Credit: The Metropolitan Museum of Art, New York, Rogers Fund, 1964 (64.47)
The drawings are more than finished works; they are windows into the artist’s working process. During the Renaissance, masters continuously experimented with forms and compositions, defining details of gesture, light, and shadow. This study confirms that these sketches were critical arenas of invention and artistic experimentation, not merely preparatory steps.
To explore these secrets, the scientists did not use destructive methods. Instead, they combined advanced microscopy, multispectral imaging (capturing light from ultraviolet to infrared), Raman spectroscopy, and powerful X-ray fluorescence (XRF) mapping. This latter technique makes it possible to create elemental maps that show, for example, the exact distribution of iron from a red chalk or lead from a highlight across the entire surface of a drawing.
The findings: layer by layer, stroke by stroke
The results, organized by type of material, paint a fascinating picture of technical mastery.
Raphael’s red chalk: In three drawings by Raphael—Studies of the Christ Child, Small Head, and Virgin and Child (recto)—the analysis confirmed the use of an iron-rich red chalk, a natural oxide that requires no binder. Elemental maps showed iron and, in some cases, manganese, a naturally associated component. Raman spectroscopy identified the material specifically as red ochre.
The study details how Raphael varied the pressure and angle of the chalk stick: fine, defined lines for contours, and soft, diffuse strokes to create shading and volume, demonstrating exquisite control of the medium.
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Perugino, Study of a Kneeling Youth, 1500.a Visible light image, where the blue arrow indicates the location of the details shown in (d) and (e). b Ca (white) distribution map showing the brushstrokes in the application of the bone ash preparation, where the blue arrow indicates metalpoint stylus incisions in the preparation layer as illustrated in Fig. 8. c Hg (red) distribution map reflecting the use of an amalgamated Ag metalpoint. d Detail of visible light image, showing lines of metalpoint (brown) and of the C-based black medium (black). e Detail of infrared image corresponding to the same area as d, illustrating the black C-based medium and the transparency of the Ag amalgam metalpoint. Close examination of the strokes shows how Perugino manipulated the character of the drawing via the angle and pressure of application. Credit: The Metropolitan Museum of Art, New York, Bequest of Walter C. Baker, 1971 (1972.118.265)
Hidden lead white highlights: In Studies of the Christ Child, ultraviolet fluorescence imaging revealed a surprise: the presence of touches of lead white applied with a brush in areas of greatest volume in the figures. These highlights, intended to emphasize three-dimensionality and the direction of light, are not visible to the naked eye.
Their appearance under UV light suggests that the pigment was originally bound with a drying oil that, over time, has become more transparent. XRF mapping confirmed the presence of lead in these areas. This finding offers insight into the artist’s original intention.
Iron-gall inks: a variable chemical fingerprint: The characteristic golden-brown ink of many old drawings is often iron-gall ink. The study analyzed its use in the Study of a Nude Male Figure (on the verso of the Virgin and Child) and in Lucretia by Raphael, as well as in Leonardo’s drawing. The maps show that iron is the main component, but its “recipe” varied.
While in Lucretia the ink contained mainly iron, in the Study of a Nude Male Figure and in Small Head manganese was also detected, and in the latter, zinc as well. These differences reflect natural variations in the iron vitriols (sulfates) used and in historical recipes, which combined galls, an iron mineral, and a gum such as gum arabic.
Leonardo da Vinci, Compositional Sketches for the Virgin Adoring the Christ Child. a Visible light image, b False-color infrared image, where iron gall ink appears as red in the areas where it was more heavily applied, and metalpoint shows in black. c Photomicrograph showing the heavy iron gall ink application in the area indicated by the blue arrow in (b). Original magnification: 30×. Credit: The Metropolitan Museum of Art, New York, Rogers Fund, 1917 (17.142.1)
In Lucretia, the analysis went further. Beneath the final ink drawing, a preliminary sketch executed with a carbon-based black medium (such as charcoal or lamp black) was discovered, identified by Raman spectroscopy. In addition, on the verso of the sheet, a layer of this same black medium was found, friable and applied densely.
This, together with the presence of incised lines on the recto, is clear evidence that the drawing was used as a template to transfer the design to another surface using a method known as “pouncing” or tracing, a common practice in workshops.
The world of metalpoint: This technique, which uses a metal stylus on a prepared paper, yielded some of the most technical findings. In Raphael’s Study of a Nude Male Figure, XRF mapping revealed leadpoint lines (which require little preparation) beneath the iron-gall ink, showing the process of initial sketching followed by reinforcement.
Perugino’s drawing, Study of a Kneeling Youth, showed a highly visible sheet preparation based on bone ash (rich in calcium and phosphorus), identified by Raman spectroscopy. On top of it, Perugino used a stylus made of a silver–mercury alloy (silver amalgam). Mercury was detected by XRF, and spot analysis confirmed the presence of silver.
The use of amalgamated silver may have been underreported due to the difficulties of identifying it without chemical imaging, the study notes. Raking-light microscopy showed how the stylus even physically incised the preparation layer, demonstrating its malleability.
Leonardo’s pink preparatory layer: Leonardo’s drawing, Compositional Sketches for the Virgin Adoring the Christ Child, presented one of the most complex systems. The sheet was prepared with a colored layer of a pinkish tone. Raman analysis identified the pigment as minium (red lead), a red lead oxide, mixed with bone ash and particles of calcium carbonate.
Dyeing preparations with tones such as pinks, violets, greens, blues, grays, and reds expanded the artist’s options, the article explains, acting as a mid-tone that broadened the available range.
On this base, Leonardo first drew with a metalpoint of silver amalgam that also contained some copper. He then overlaid and continued working the composition with iron-gall ink, rich in iron. The elemental maps make it possible to distinguish, for example, that the sketches of babies in the lower central area were made only with metalpoint (they appear in the silver and mercury maps, but not in the iron map), while in other areas both media overlap.
This technical study of drawings by Raphael, Leonardo da Vinci, and Perugino demonstrates how the integration of non-invasive analytical techniques can enrich our understanding of Renaissance drawing. The images, chemical maps, and molecular analysis revealed complex layering strategies and material choices—often invisible to the naked eye—that speak both to shared conventions and to the individual preferences of these artists.
The study concludes unequivocally: Without the application of advanced imaging and mapping techniques, some of these observations, including the specific use of amalgams in metalpoint and the material compositions of preparatory surface treatments, would have remained undetected. This research affirms the essential role of scientific analysis in uncovering the material choices of Renaissance artists and offers a model for future studies at the intersection of conservation science and art historical research.
SOURCES
Centeno, S.A., Mustalish, R. & Ramsey, L.M. Materiality and techniques revealed in drawings by Raphael, Leonardo da Vinci, and Perugino. npj Herit. Sci. 13, 597 (2025). doi.org/10.1038/s40494-025-02175-y