Preliminary Investigation of Sri Lankan Copper-alloy Statues

Abstract The historical framework for the discussion is the chronology of Sri Lankan culture, which, based on the most recent archaeological evidence and radiocarbon dates, has been defined by three major periods: Early Historic (500 BC-300 AD), Middle Historic (300 AD-1200 AD) and Late Historic (1200 AD-1815 AD). A classification for the evolution of bronze sculpture with reference to the established historical chronology for Sri Lanka has been proposed by Reedy (2007) who sets out the following four major developmental periods of Late Anuradhapura (ca.432–993 AD), Polonnaruva (late 10th to early 13th century), Divided Kingdoms (13th to late 16th century), and Kandyan (17th to 19th century). This technical study investigated thirty sculptures including 25 tin bronzes in The Metropolitan Museum of Art and five from the Archaeological Department of Sri Lanka, representing all four major historic periods. The methods used to analyse the manufacture, composition, and condition of the statues were examination under magnification and Ultraviolet light, X-ray radiography, elemental analysis using X-ray fluorescence spectroscopy, and metallography. The results of the study included the finding that all the statues in the sample were cast using the lost-wax technique. Size does not seem to have had a bearing on whether statues were cast solid or hollow. Many of the small seated figures in the sample were solid cast, while a few were hollow cast. In addition the radiographs indicate that a variety of armatures of different thickness, size, and shape were present inside the hollow figures, irrespective of the size of the statues. Generally, metal of low porosity and few casting defects are observed in most of the radiographs, indicating that the castings are generally of good quality. Traces of five gates (or vents) observed on the backs of a group of five Lokapala figures examined, indicated that they were cast face-down in a horizontal position. Ten figures, particularly those from the later periods, show traces of gilding or intact gold layers. In all but one case, gold was found in association with mercury, confirming that they were amalgam gilded. Metallurgical studies were carried out on four figures in the sample: a Buddha, a Bodhisattva and two Hindu deities. A sample from a tang that was cast onto the goddess figure in antiquity proved to be quenched high-tin bronze, as evident from its microstructure; a tin content of 24.8 w/o was confirmed using X-ray energy dispersive spectroscopy in a scanning electron microscope. The four statues were from different historical periods and showed different microstructures, reflecting dissimilarities in composition, thermal history, and state of preservation.