Abstract
Macroscale multimodal chemical imaging combining hyperspectral diffuse reflectance (400–2500 nm), luminescence (400–1000 nm), and X-ray fluorescence (XRF, 2 to 25 keV) data, is uniquely equipped for noninvasive characterization of heterogeneous complex systems such as paintings. Here we present the first application of multimodal chemical imaging to analyze the production technology of an 1,800-year-old painting and one of the oldest surviving encaustic (“burned in”) paintings in the world. Co-registration of the data cubes from these three hyperspectral imaging modalities enabled the comparison of reflectance, luminescence, and XRF spectra at each pixel in the image for the entire painting. By comparing the molecular and elemental spectral signatures at each pixel, this fusion of the data allowed for a more thorough identification and mapping of the painting’s constituent organic and inorganic materials, revealing key information on the selection of raw materials, production sequence and the fashion aesthetics and chemical arts practiced in Egypt in the second century AD.
Highlights
Advances in technology and miniaturization of chemical imaging technologies – adapted mainly from airborne scanners – including reflectance hyperspectral imaging (HSI) in the visible and shortwave infrared region (VSWIR, ~400 to 2500 nm) and scanning macroscale X-ray fluorescence (MA-XRF) spectroscopy[1,2,3,4,5,6,7], have enabled their deployment in the field and in museums, making enormous strides for in situ noninvasive characterization and analysis of important works of art ranging from Old Masters’ and modern paintings, to wall paintings and polychrome archaeological artifacts
Types of spectra for a given pixel, allowed for a more thorough identification and mapping of the painting materials. This is the first application of multimodal imaging spectroscopy on an archaeological panel painting over eighteen hundred years old, abetting fingerprint identification of the organic and inorganic constituent materials and the chaîne opératoire – the operation sequence by which raw materials were selected, processed, and transformed into a cultural object
For the characterization of organic materials used as paint binding media, such as lipids, carbohydrates and proteinaceous materials, spectral bands in the mid-infrared related to fundamental vibrational transitions are typically used
Summary
Advances in technology and miniaturization of chemical imaging technologies – adapted mainly from airborne scanners – including reflectance hyperspectral imaging (HSI) in the visible and shortwave infrared region (VSWIR, ~400 to 2500 nm) and scanning macroscale X-ray fluorescence (MA-XRF) spectroscopy[1,2,3,4,5,6,7], have enabled their deployment in the field and in museums, making enormous strides for in situ noninvasive characterization and analysis of important works of art ranging from Old Masters’ and modern paintings, to wall paintings and polychrome archaeological artifacts. For the analysis of ancient paintings, multimodal imaging spectroscopy offers unparalleled potential in identification of both organic and inorganic materials, hitherto impossible without sampling and microanalysis It further enables the mapping of both molecular and elemental data for every pixel in the image across the entire surface of the painting, aiding in accurate attributions and interpretations and informing on production technology and raw materials selection. We demonstrate the potential of multimodal chemical imaging spectroscopy with results from the fusion of the three data cubes obtained from diffuse reflectance and luminescence HSI and MA-XRF spectral imaging modalities, employed for the analysis of a complex and archaeologically significant Greco-Roman painting (“Portrait of a Woman”) of the second century AD, from the collection of the National Gallery of Art in Washington DC (Fig. 1). The jewelry consists of a pendant earring and three necklaces, inlaid with what appear to be pearls and gemstones
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