In Situ Noninvasive Study of Artworks: The MOLAB Multitechnique Approach

Abstract

Driven by the need to study precious and irreplaceable artworks without compromising their integrity, researchers have undertaken numerous efforts to develop noninvasive analytical tools and methodologies that can provide a chemical description of cultural heritage materials without any contact with the object. The challenge is that artworks are made of complex mixtures, often with heterogeneous and unknown layered materials. Their components must be identified over a range of size scales, from the molecular identification of constituent compounds to the mapping of alteration phases. In this Account, we review recent research in spectroscopic techniques accessible from the mobile laboratory (MOLAB). The lab is equipped with an array of state-of-the-art, portable, and noninvasive instruments specifically tailored to tackle the different issues confronted by archaeologists, curators, and conservators. The MOLAB approach is suitable for studying a variety of objects, from ceramics to manuscripts or from historical wall paintings to contemporary canvases. We begin by discussing issues related to the acquisition and interpretation of reflectance or backscattered spectra from the surface of heterogeneous materials. Then we show how the selectivity needed for the noninvasive identification of pigments in paintings, even in mixtures or in layered matrices, can be acquired by combining elemental information from X-ray fluorescence with molecular and structural insights from electronic and vibrational spectroscopies. Discriminating between original pigments and restoration retouches is possible, even when both comprise similar chromophores, as highlighted in the study of paintings by Jordaens and Raphael. The noninvasive approach permits the examination of a very large number of artworks with a virtually limitless number of measurements. Thus, unexpected and uncommon features may be uncovered, as in the case of a lead pyroantimonate yellow doped with zinc that was discovered by micro-Raman and X-ray fluorescence on an Italian Renaissance majolica. For characterizing binding media, we discuss the strengths and limitations of using mid- and near-FTIR (Fourier transform infrared) spectroscopies supported by a multivariate statistical analysis, detailing the study of organic materials in a wall painting by Perugino and a survey of the painting technique on 18 contemporary paintings by Burri. In Michelangelo's David, we show how the noninvasive mapping of contaminants and alteration phases might inform decisions on preventive conservation plans. The multitechnique MOLAB approach overcomes the intrinsic limitation of individual spectroscopic methods. Moreover, the ability to analyze artworks without the need to move them is an invaluable asset in the study and preservation of cultural heritage.

Disclosing Jackson Pollock’s palette in Alchemy (1947) by non-invasive spectroscopies

“…The mobile laboratory MOLAB is a collection of integrated mobile instruments based on a variety of noninvasive spectroscopic methods exploiting light-matter interactions (reflection, scattering and emission) in different spectral ranges, (from infrared to X-ray), and with different detection methods (point analysis and multispectral imaging) [1,6]. In this study, the multitechnique approach of MOLAB has been called to face an unusually challenging task: identifying the palette of the American abstract expressionist J. Pollock, in his iconic painting Alchemy (1947, Peggy Guggenheim Collection, Venice-Additional file 1.…”

A multi-technique approach, based on mobile/portable laser instruments, for the in situ pigment characterization of stone sculptures on the island of Crete dating from Venetian and Ottoman period

“…Collecting microsamples is often an alternative for bypassing the above limitations, but current trends, concerning protection and preservation of cultural heritage objects, impose non-sampling policies or strict controls in performing sampling for further analysis in the laboratory. Obviously the option to use mobile analytical equipment, which can be operated on site, emerges as an important prospect [1][2][3][4][5].…”

MOLAB®meets Persia: Non-invasive study of a sixteenth-century illuminated manuscript

“…1 Since manuscripts require particular care due to their intrinsic fragility and susceptibility to damage due to changes in environmental conditions, the MOLAB ® non-invasive multi-technique approach (Miliani et al, 2010) offers a reliable and sensitive way to study the materials the manuscripts are made of, in situ. Furthermore, MOLAB ® has extensive experience with studies of manuscripts of different provenance and periods, acquired during its investigations in many European museums and libraries (Miliani et al, 2012;Doherty et al, 2013;Buti et al, 2014;Sgamellotti et al, 2014).…”