Discovering the material palette of the artist: a p‐XRF stratigraphic study of the Giotto panel ‘God the Father with Angels’

Abstract

Elemental analysis, and in particular stratigraphic distribution of elements themselves, is a fundamental method to address the composition of materials, but its nature, often invasive, crashes with the necessity of avoiding artefacts' damage when dealing with Cultural Heritage objects. In fact, when work of art are involved, sampling is often forbidden, and transferring an artistic artefact to equipped laboratories is a not negligible issue. The skill to employ in situ non‐destructive and non‐invasive analytical method is essential. In this scenario, portable X‐ray fluorescence (p‐XRF) has become one of the most employed techniques due to the development of adaptable and open architecture instruments. In this paper, we show a new data analysis protocol and its application to XRF data acquired from a work by Giotto never studied before: ‘God the Father with Angels’ (ca. 1330, San Diego Museum of Art). The measurements have been performed in situ during the closing time of the exhibition ‘Giotto, l'Italia’ (Milano Palazzo Reale – 2 September 2015/10 January 2016). Combining the effectiveness of scanning p‐XRF with the responsive of image spectroscopic analysis, we move step by step toward the discovery of Giotto's palette for the flesh tones in God the Father with Angels; our method allows to argue the stratigraphy of the painting without complementary measurements and, at the same time, provides a sequential and smart representation of complex data. Copyright © 2017 John Wiley & Sons, Ltd.

More than XRF Mapping: STEAM (Statistically Tailored Elemental Angle Mapper) a Pioneering Analysis Protocol for Pigment Studies

“…As an example of the flexibility and of the enormous potential of XRF mapping, we are introducing and discussing a pioneering analysis protocol called STEAM, Statistically Tailored Elemental Angle Mapper. Based on the SAM algorithm and on the Global Spectrum (GS) analysis introduced by Galli and co-workers [46], STEAM first accomplishes the tasks of the MA-XRF typical approach (i.e., it maps the elemental distribution [10,14]) and then, in synergy with punctual XRF, it exploits the information gathered from the mapped area(s) as a database to extend the comprehension to data outside the scanned region(s). The protocol works independently from the acquisition set-up and, once defined the main features of the database, it sheds light on uncharacterized data, disregarding their origin and their relationships with the scanned region(s).…”

“…This choice finds its rationale in the fact that the features of the database must constitute the starting point for STEAM, and therefore they must be well characterized. The area in Figure 1 has been exhaustively described by Galli and co-workers [46]; therefore, its main features can be considered as known. For what concerns the application of our protocol, the main results of the quoted paper can be summarized as follow: the results referring to the left half of the scanned area mainly compliant with the technique used by Giotto in the Croce of Santa Maria Novella, a double layer providing a Cinnabar-White Lead mixture (elementally dominated by the couple Pb-Hg) superimposed to a gypsum-Verdaccio lower layer (Ca-Sr and Fe-K couples) [47].…”

“…The mockup paintings, drawn in separate areas, are made of a few layers combined in different ways to verify if the method was able to discern within similar, but different, cases. Pigment choice has been based on the palette used by Giotto for the flesh tones of the gable of San Diego [15,46]. In order to account for the irregular thickness of the painted panel, three XRF spectra have been acquired by Bruker Artax 200 spectrometer for each layers' sequence and the average spectra have been used to test the performance of the protocol.…”

“…The choice of these points follows the twofold purpose to verify hypotheses fro previous studies [15,46,48] and, if possible, to gather new insights into the gable's featur Since the right part was supposed to be more affected by restorations with respect to left one, the same tones have been collected on both groups of angels to compare the us pigments. Moreover, the book held by God has been investigated because the authentic of the letters typed on the pages is still debated.…”

Design and Analysis of Cable-Driven Parallel Robot CaRISA: A Cable Robot for Inspecting and Scanning Artwork

“…Handheld operation limits the analysis to isolated spots and, consequently, does not allow for acquisition of representative data. Tripod-mounted devices can be positioned more freely and can, to some extent, account for surface curvature, yet their scanning range is only a few hundred square centimeters [6]. Table-mounted devices allow for scanning large areas, and, in some cases, can also follow the surface to keep a constant distance, however, the measurement head cannot be panned or tilted [17].…”