Person:

Eremin, Katherine

Samples from Thai manuscripts dated to the 18th to 20th century were analyzed by Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR) to determine the pigments used. This suggested a change in palette from the 18th to 20th century, with use of imported pigments in the later manuscripts. In the 18th century, the main green used was an organic copper salt, which was replaced by emerald green and mixtures of Prussian blue with gamboge, chrome yellow and zinc yellow (zinc potassium chromate). Chrome yellow was used in addition to gamboge in one later 19th century manuscript. Similarly, indigo in the 18th century manuscripts was replaced by Prussian blue and then synthetic ultramarine in the 19th century manuscripts. Lead white was the main white pigment in all but one manuscript, which contained huntite, a magnesium calcium carbonate. Huntite also occurred in mixtures with other pigments in two other manuscripts. In all the works studied, red lead, vermilion and red earth were used for red, orange and pink shades and red earth in brown areas. The organic copper salt used in the 18th century gave good FTIR spectra but could not initially be matched with any published compound. X-ray diffraction (XRD) suggested this was a copper citrate phase, and examination of the literature showed that the FTIR spectra matched those published for a hydrated copper citrate. Raman spectra were obtained from this organic copper salt, which showed close agreement with those obtained from synthetic copper citrate. Copper citrate has not been identified previously as an artist’s material, although its use has been postulated on the basis of historical texts. Minor copper formate and/or copper chloride were also identified by XRD and scanning electron microscopy (SEM) in some green samples containing copper citrate.

This study characterizes the materials and construction methods of a fourth- to fifth-century ce over-lifesized, polychromed head of a Buddhist figure in the collection of the Harvard Art Museums that is believed to be from Hadda, Afghanistan. Many sculptures from this monastic site and others in Greater Gandhara (located in parts of modern-day Afghanistan and Pakistan) were described using the general term “stucco” by the Europeans who collected them in the early twentieth century. Through technical imaging and analysis, this investigation identifies the specific materials of this object to provide a basis of comparison for related sculptures in other collections. While a great variety of materials and techniques—used alone or in combination with others—have been identified on related objects, few of these objects have undergone imaging and analysis to verify materials and visualize construction methods. Examination and analytical methods used in this study included visual examination, micro-computed tomography (micro-CT), radiocarbon dating, and materials analyses by x-ray fluorescence (XRF), scanning electron microscopy with energy dispersive microanalysis (SEM-EDS), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and thin-section petrography. The micromorphology and analysis of samples indicated that the solid head is composed of a lime stucco mixture including varied silicates and carbonates (both calcite and dolomite), and inclusions of fired ceramic and rock fragments. This mixture was applied in layers in situ starting with a coarse-grained core and finishing with a fine layer, with a higher proportion of lime binder. A wooden post, with a likely nineteenth-century date, is embedded within the damaged internal structure and may have been added to replace part of an original armature. Pigments used for polychromed details were identified as ochers and carbon black, with limited use of red lead.