Art historians display something close to mystical reverence when discussing possible finger and palm prints on Leonardo da Vinci’s paintings, but other such personal marks have received little attention in fine arts research. Džemila Šero, who worked on documenting finger marks on artworks for her postdoc research at the Centrum Wiskunde & Informatica in Amsterdam, offers an explanation for the fact that these marks have frequently been neglected and scarcely reported in museum records: ‘It’s probably because curators lacked the means to properly document them, other than just photographing them, and there was no possibility to effectively compare them to other marks.’

Hovering Putto

Šero’s work resulted in a standardized procedure for scanning various marks found on the surface and inner walls of terracotta sculpture using 3D micro–computed tomography, published in Science Advances. While this method needs more sophisticated equipment than standard photography, and experts who know how to process and interpret the data, it provides a more detailed and objective ground for comparison, with the ability to digitally enhance images to make the proper calculations. ‘On our test object, the terracotta sculpture Study for a Hovering Putto attributed to Laurent Delvaux from the collection of the Rijksmuseum, we identified eight partial fingermarks on the visible surface, five in inner voids, and three impressions that we interpreted as toolmarks.’

Šero and her team have proposed a method to interpret these marks, based on research in forensic archaeology that focused on such marks on ceramics. Changes in ridge breadth and ridge density are mainly influenced by advancing age and the typical differences in body shape and size between males and females. Research suggests that there are three more or less distinct age groupings that can be ascertained on the basis of finger marks: one group of prepubescent children, a group of adult males and a mixed group of adolescents, adult women, and men.

This seems a rather course division, but Šero explains that it is valuable information to have when considering historical studio practice: ‘Most mature artists worked closely with much younger pupils in their studios, so that difference might become apparent on artworks to which both the master and pupils contributed. Even with the Hovering Putto we investigated, we don’t know yet for sure how many persons were involved. Museum records for this specific sculpture say that it’s by Delvaux himself, but our data do not specifically point to one maker.’ Most of the calculations for ridge density, corrected for shrinkage during firing, indicate an adult male maker.

Professional vs. Volunteer

However, additional experiments conducted by the research team suggest that some caution is warranted when interpreting finger marks. The research team asked a trained female ceramicist and an untrained volunteer to leave their impressions on fresh clay. The volunteer had the express intention of leaving a clean mark with extreme care. His impressions were indeed clear and clay irregularities almost imperceptible. The marks by the female ceramicist were impressed on the clay casually, and these were thinner in depth and interrupted by clay inhomogeneities. Furthermore, calculations based on the marks left by her indicated that these would actually have been made by an adult male.

Moreover, not every lined mark on an artwork is necessarily left by a finger or hand. Artists used a wide range of tools to work and finish the surface. Šero: ‘In some cases the difference is straightforward, because the marks are really wide, but sometimes those striations do look like a smeared fingerprint. But by running the experiments under controlled settings, we realized that the depth of the impressions left by fingers almost all of equal depth, while tools such as a brushes with hard hairs may display slightly different depths because of the varying hair lengths.’

Carving tool marks

While the unicity of finger marks is obvious, other marks could also prove to be distinctive for a single maker or workshop. ‘It was common practice in the 18^th century to customize each carving tool on the artist’s requests,’ Šero explains, ‘so the corresponding toolmarks represent distinguishing traits of the artist and workshop practices.’ Further research based on their procedure could make it easier to distinguish tool marks from ones left by hands or fingers, especially when these are only partial impressions. 

In this sense, Šero’s research marks the first steps into a new field of study, one in which more data is needed to make comparisons possible: in order to connect, we need to collect. ‘If you have a partial mark with discriminative points that you cannot match elsewhere, it is always possible that you might encounter another sculpture in the future, modeled in the same workshop, that produces a match after all. That’s why it is so important to have data collected and stored in a standardized way, so that anyone working on these objects in the future can consult these databases and advance our knowledge.’

Šero, D. et al. (2023) Sci. Adv. 9(38), DOI: 10.1126/sciadv.adg6073