Pigment Analysis of Two Thai Banner Paintings
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1047-Y06-05
Pigment Analysis of Two Thai Banner Paintings Jennifer Giaccai Conservation Division, Walters Art Museum, 600 North Charles Street, Baltimore, MD, 21201 ABSTRACT The pigments used in two Thai banner paintings (phra bot) were examined using X-ray fluorescence (XRF), Fourier transform infrared microscopy (FTIR) and polarized light microscopy (PLM). The two paintings examined dated from the late 18th and the late 19th century. The paintings examined follow the trends observed on Thai wall paintings and manuscripts from the same time periods. Pigments identified include vermilion, iron oxide earths, red lead, lead white (hydrocerrusite), calcium carbonate, kaolin, Prussian blue, gamboge, artificial ultramarine, copper citrate and a copper-arsenic green. INTRODUCTION Despite interest in the use of pigments in Thai painting on the part of art historians, the few technical examinations of these works have focused on wall paintings and manuscripts. As a part of the recent conservation of Thai wall paintings, the pigments used in the wall paintings were identified.[1,2] One study of four Bangkok period Thai manuscripts held by the British Library has been published, and a study of twelve manuscripts from the 17th to the 20th centuries in the collection of the Harvard University Art Museums has recently been completed.[3,4] In the previous studies of Thai pigments, the most notable pigment differences found were the changes in green, white, and blue pigments. Prasartset observed a shift from malachite to the man-made emerald green pigment over the course of the 19th century. Eremin et al found that the most commonly used green pigment in manuscripts before the introduction of emerald green was a copper citrate pigment (Cu2(C6H4O7).(H2O)x). Emerald green (copper acetoarsenite, 3Cu(AsO2)2.Cu(CH3COO)2) quickly moved into the palettes of European artists by the mid-19th century and just as quickly was added to Asian palettes.[5,6] The murals used a clay based white pigment in the early 18th century, and showed the addition of lead white (basic lead carbonate, 2PbCO3.Pb(OH)2) beginning in the 18th century. Although barite mineral is naturally occurring in Thailand, barium sulfate (BaSO4) was only identified in late 19th-century mural paintings.[2] Similar changes in pigment use in manuscripts were described by Burgio et al., who identified barite as well as anhydrite (CaSO4) and gypsum (CaSO4.2H2O) in an early 20th-century manuscript.[3] Eremin identified a variety of white pigments, including lead white, calcite (CaCO3), kaolin (Al2Si2O5(OH)4), and huntite (CaMg3(CO3)4).[4] All previous studies observed a change in blue pigments, from azurite (2CuCO3.Cu(OH)2) or indigo (C16H10N2O2) to Prussian blue (Fe7(CN)18(H2O)x) in the early 19th century and finally to ultramarine ((Na,Ca)8(AlSiO4)6(SO4,S,Cl)2) in the late 19th century. Prussian blue very quickly made its entry into the artistic world; from its discovery around 1704 it was used by artists in Europe only twenty years later,[7] and was traded in Asia by 1775.[8] Pr
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