Beyond the visible: The Viterbo Crucifixion panel painting attributed to Michelangelo Buonarroti

Highlights

• The Viterbo Crucifixion panel painting, attributed to Michelangelo Buonarroti, has been subject of multi-analytical scientific analysis to support and explain the hypothesis about the painting attribution and dating

• A novel hypespectral camera, capable of high optical throughput and hence requiring limited irradiance on the painting surface, have been tested on the painting

• Hyperspectral imaging and X-ray fluorescence spectroscopy have identified the use of the precious ultramarine blue and vermillion pigments, confirming the importance of the painting committer.

• Wiggle matching dating revealed a very important datum for the historical location of the painting (AD 1500 ± 25) giving to the art historians a further element for the attribution of the artwork.

Abstract

The painting object of the present work, currently exposed in the Museum of Colle del Duomo in Viterbo (Italy), has been dated back by art historians to the 16^th century and it owes its relevance to a still discussed attribution to Michelangelo Buonarroti. For this reason, art historians and the responsible curator of the Museum commissioned scientific investigations to support and explain their hypothesis about the painting attribution and dating. Here we report the results of two sets of investigation: diffuse reflectance hyperspectral imaging and X-ray fluorescence spectroscopy of the painting; radiocarbon dating and identification of the panel wood. The hyperspectral dataset, coupled with X-ray fluorescence spectra on selected analysis points, reveals the presence of precious ultramarine blue and vermillion pigments, confirming the importance of the painting committer. Wood analysis and radiocarbon dating by wiggle matching technique revealed that the botanical species used for the panel is Cypress (Cupressus sempervirens L.), and enabled dating the painting around AD 1500± 25, providing to art historians a further element for the attribution of the artwork.

Introduction

The “Viterbo Crucifixion” is an interesting 16^th century panel oil painting (59 × 46 cm), representing a Crucifixion, exposed in the Museum of Colle del Duomo in Viterbo (Italy) (Fig. 1) [1], [2], [3], [4]. The great interest around this little panel painting is due to its attribution to the workshop of the Master Michelangelo Buonarroti. This hypothesis was made after the discovery of a will, dated 1725, reporting that a crucifixion by Michelangelo was donated to the Jesuits of Viterbo by Paolo Brunamonti [5]. Even though this document alone does not prove the attribution of the “Viterbo Crucifixion” painting to Michelangelo, there are some elements, such as the presence of Buonarroti in Tuscia and his relationship with Vittoria Colonna and with the reform movement known as Spirituali (or ecclesia viterbiensis), that suggest that an artwork of the Master should be present in Viterbo [5], [6], [7], [8], [9], [10], [11]. The deep friendship between Michelangelo and Vittoria Colonna, well-documented by their extensive epistolary relationship, had probably a role in the spiritual nearness of Michelangelo with the Ecclesia Viterbensis and influenced Michelangelo's artistic thought and production, as reported in various relevant studies [8], [9], [10], [11], [12], [13], [14].

Some interesting elements of the “Viterbo Crucifixion” painting support the proposed attribution hypothesis. One is the unusual landscape at the back of the cross: a view on a towered town, which recalls the present Porta Faul in Viterbo, while the ruins in the background evoke the Bacucco thermal baths [12].

A second interesting element of the painting concerns a garment detail, the perizoma of Christ that exhibits a quite anomalous pink hue. Indeed, in liturgical terms this is usually referred to Easter, and not to Crucifixion. According to Elisabetta Gnignera [12], the use of this unusual colour should be associated to the peculiar thinking expressed both by the Spirituali and by Vittoria Colonna (in two of her spiritual sonnets) that considers the death of Saviour as a joyful event because of man's salvation in Christ. Indeed, the anomalies and variants in the Crucifixion of Colle del Duomo (in comparison, for example, with later replicas by painter Marcello Venusti) strengthen the hypothesis of a link between this artwork and the religious debate that originated immediately after the publication in 1543 of the book Beneficio di Cristo (The Benefit of Christ's Death), which reflects the radical thinking of the Spirituali [13].

Another important element that contributes to the possible attribution of the painting is a letter by Vittoria Colonna [14], where she mentions a Crucifixion that she received from Michelangelo, and where she inquiries about its authorship (she wrote: … per il che ho risoluta de non volerlo di man d'altri, et però charitemi, se questo è d'altri, patientia … that is “as long as I don't want it if painted by others, please tell me if it is a creation of another painter”).

According to art historians, the Crucifixion painting has other peculiarities: the anomalous appearance of Christ's face, very different from the rest of the figures; the plausible later addition of the figure of Magdalene at the foot of the cross; the face of Saint John, that changes when observed under different illuminations.

The later inclusion of Magdalene is presumed from the overlap of her garment to the Virgin's mantle; furthermore, on Magdalene's right shoulder some art historians recognise an anachronistic buckle, which was in use only from the second half of the 16^th century (private communication from art historian Elisabetta Gnignera, specialist on Renaissance).

Art historians speculate that the change in Christ's face and the possible addition of Magdalene are a consequence of the 1556 catholic reforming decree of Pope Paul IV (born Gian Pietro Carafa), where some dictates in religious painting representations are established, including the fact that it was forbidden to depict the crucified Christ alive [15].

St. John's face is particularly intriguing since it has a female aspect when observed under visible illumination, but it assumes more masculine traits and a hollowed aspect when observed under UV excitation [1,4]. This phenomenon, which occurs only in the face of St. John and hence appears intentional, highlights a further link between Michelangelo and Vittoria Colonna. In fact, art historians relate this effect to a circumstance mentioned by Vittoria Colonna in her letter “del lume” (“about the lamp”) to Michelangelo (presumably between 1543 and 1544) [2], where Vittoria Colonna expressed her astonishment regarding a “Crucifixion” sent her by Michelangelo, which she had “well observed with a glass, a lamp and a mirror” (“Io l'ho ben visto al lume et col vetro et col specchio, et non viddi mai la più finita cosa”). Noticeably, in another letter written between 1542 and 1543, Vittoria Colonna requested to Alvise Priuli, the secretary of Cardinal Reginald Pole (leader of Spirituali at Viterbo), some green-coloured glass manufactured in Venice (“quell vetro verde che venne da Venezia”) to donate to Michelangelo who, at that time, was working to the wall paintings of the Cappella Paolina in the Vatican palace [16]. It is beyond the scope of this paper to investigate whether and how Michelangelo made use of coloured glasses, but the optical properties of glass materials were empirically known since the age of ancient Romans [17], while at the Renaissance time it was common to admire works of art through coloured optical glasses, as it is well documented for several artists and patrons [18].

In this debated context, a further study of the Crucifixion was requested by the responsible of the Museum and by art historians of Egidio17 project, which focuses on the historical panorama in Viterbo in the first half of 16^th century [2].

In this paper, we discuss the results of some of these further analyses, achieved by combining diffuse reflectance hyperspectral imaging (HSI) [19], punctual X-ray fluorescence spectroscopy (XRF), wood characterization and wiggle matching dating, with the aim of investigating both the paints and the wooden panel of this small, but long-discussed painting. The HSI dataset and the XRF spectra on selected analysis points contribute to the knowledge of paint materials, techniques and pictorial details of the panel, and the related findings are compared with Michelangelo's artistic thought and production. Wood analysis enables the characterization of the botanical species and the peculiarities of the wooden panel, a further relevant aspect for the analysis and attribution of the painting [20], [21], [22], [23], [49]. In particular, the identification of the botanical species provides important information to set the wooden artefact in a clear geographical and cultural context. At last, radiocarbon dating, through wiggle matching technique, was performed for establishing a chronological range for the wooden panel [24].