False Color and Infrared Imaging for the Identification of Pigments in Paintings
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False Color and Infrared Imaging for the Identification of Pigments in Paintings Dulce María Aguilar-Téllez, José Luis Ruvalcaba-Sil, Pieterjan Claes, Diana GonzálezGonzález Instituto de Física, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica s/n, Ciudad Universitaria, Mexico DF 04510, Mexico. e-mail: [email protected] ABSTRACT In the study of cultural heritage, most of the analytical techniques are point-specific or give information about small areas of the object. Therefore it is essential to obtain an overview of which points are suitable for these further investigations. To fulfill this, a first imaging study is the best way to proceed. Hereby, we can record the entire piece at once and observe the behavior and relation between different materials of the object. Various types of light can be used to obtain a selection of images and consequently also different information about the artifacts. Among them, infrared (IR) photography can be used as a first analysis, for instance, to reveal the pigments’ response upon interaction with IR radiation. In following we will present results obtained via IR video-photography on a selection of painted objects from the Mexican cultural heritage. These items are analyzed by False Color procedure, where colors are assigned to every grey tone of the pure IR photo. Hereby it is possible to distinguish between certain pigments on the painted surface. INTRODUCTION Throughout the years, photography has been used in all its forms as a highly valuable tool in art and various fields of science, but also for its wide range of possibilities and multiple applications in archaeology and conservation [1], for instance in aerial and excavation photography [2-7], examination of tattoos found on human remains [8], the study of pigments on textiles [9-10], documents [11-14] and paintings [15-18]. Due to its non invasive nature, a photographic study is considered as a non-destructive method. Therefore, it serves as a complementary technique to support results obtained by the versatile range of atomic and molecular studies available, such as X-ray fluorescence (XRF), Raman and infrared (IR) spectroscopy. Additionally, when conducted as a first, indicative examination, a thorough photographic study also provides valuable information for further investigations about interesting areas and points of the studied artifact for spectroscopic analyses. A photographic study of archaeological or art-historical pieces usually involves the use of various kind of illumination. For this, several types of light (visible (VIS), ultraviolet (UV) or infrared (IR) light) can be used, depending on the type of information one wants to obtain. UV pictures, for instance, taken under illumination with UV light, provide evidence of a certain behavior via the fluorescence of the different pigments in the painting. IR imaging, on the other hand, shows the IR response of the materials via differences in gray tones. A painted surface is usually built up of different layers, such as pigments,
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