Inside and Out: A Technical Investigation of Clay Buddhist Objects from Khara Khoto | Index Magazine | Harvard Art Museums document.getElementById('article-date').offsetTop"> Headless Seated Figure, Central Asian, Tangut Xia period, 12th century. Sun-dried clay with polychrome pigments. Harvard Art Museums/Arthur M. Sackler Museum, First Fogg Expedition to China (1923–1924), 1924.65.2. As part of our series focusing on the work of conservation and curatorial fellows, Kaela Nurmi shares her technical research on a 12th-century clay Buddhist sculpture. During early planning for the 2027 exhibition Elements of Chinese Art: Materials and Making, Sarah Laursen, the Alan J. Dworsky Curator of Chinese Art, introduced me to a compelling group of 200 objects from the city of Khara Khoto, in present-day Inner Mongolia. Materials from Khara Khoto are held in only four institutions worldwide: the State Hermitage Museum, St. Petersburg; the British Museum, London; the National Museum, New Delhi; and the Harvard Art Museums. The group of Harvard objects had remained in storage for a century and had never been studied. The Harvard collection includes bronze coins, wooden stands, a single glazed ceramic fragment, and, predominantly, air-dried clay objects; all are dated between the 11th and 13th centuries. For my study during my fellowship, I focused on 20 air-dried clay Buddhist objects across the following representative categories: partial figures, plaques, heads, architectural elements, and votive objects. I planned to investigate their materials, how they were made, and their surviving surface decoration. Using visual examination, imaging, radiography, and scientific analysis, I aimed to better understand the material traditions and artistic practices of Khara Khoto while supporting the long-term stewardship of these objects. I collaborated closely with staff in the Straus Center for Conservation and Technical Studies analytical lab, specifically Katherine Eremin, the Patricia Cornwell Senior Conservation Scientist, and conservation scientist Georgina Rayner. Khara Khoto Khara Khoto was a thriving trade and Buddhist center of the Tangut-ruled Great Xia dynasty (1038–1227 CE). Its artistic traditions were shaped by both Himalayan and Chinese influences. Located along the Silk Road in what is now Inner Mongolia, this city in the Gobi Desert prospered until the fall of the Tangut empire during Genghis Khan’s final campaign in 1227.[1] In the early 20th century, several foreign expeditions removed objects under ethically problematic circumstances from the abandoned city. Langdon Warner of the Fogg Museum led the First Fogg Expedition to China in 1923–24 and brought more than 200 objects from Khara Khoto to the Harvard Art Museums.[2] Technical Investigation In the first stage of my technical study, I examined each object under magnification to assess the surface details and condition before photographing it from multiple angles to document its current state. From there, the analytical process I applied depended on the object. Most objects underwent X-radiography, and in some cases micro-CT scanning, to determine what techniques were used in their construction, including their internal structures. For objects with visible painted decoration (polychromy), I collaborated with conservation scientists to identify pigments and surface materials. The air-dried clay polychrome sculpture Headless Seated Figure is a well-preserved example of a seated figure with surviving pigment. To best illustrate my technical study process for the larger group of objects, I have outlined my investigation of the sculpture below. Case Study: Headless Seated Figure My study of Headless Seated Figure had three aims: to determine how the figure was constructed; whether it was modeled around an internal armature; and which pigments were applied to the surface. X-Radiography X-radiography answered the question about the object’s internal structure: It revealed an inner cavity lined with wood pieces, which were held together with a twine-like material and covered with clay. Adjusting the angle of the object in relation to the X-ray tube and applying filters in the imaging software helped clarify further details: Separate wood pieces in the base, visible from underneath, are embedded within the clay matrix. As a two-dimensional projection of a three-dimensional object, X-radiography can obscure spatial relationships of elements inside the sculpture. Micro-Computed Tomography (Micro-CT) Micro-computed tomography (micro-CT) was used to better understand how the sculpture was built. Unlike a standard X-radiograph, micro-CT captures hundreds of X-radiographs from multiple angles, which are reconstructed into a three-dimensional rendering that can be viewed in planes, or “slices,” across an object. These slices revealed distinct layering in the clay, with air gaps between layers. In the horizontal slices, the clay appears almost like tree rings, suggesting that the torso was built up in successive layers around the wooden cylinder core and the arms added afterward. The compression of the clay around the wood pieces in the base indicates that the clay was hand-modeled and built around each of the internal wooden supports. Examining micro-CT slices from different angles further clarified the relationship between the internal armature and modeled clay mixture. The shape of the internal wood structure was also revealed, appearing bundled and secured like a barrel. X-Ray Fluorescence (XRF) and Spectroscopy To determine the pigment composition, Katherine Eremin, the Patricia Cornwell Senior Conservation Scientist, analyzed the object’s surface using X-Ray Fluorescence spectroscopy (XRF). This non-destructive technique analyzes elemental composition, allowing for preliminary pigment identification. We tested multiple sites of each color to ensure consistency. Conservation scientist Georgina Rayner removed small samples from the sculpture and analyzed them using Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy. FTIR and Raman complement each other; FTIR is better suited for analysis of organic compounds, and Raman is particularly effective for inorganic materials. The resulting spectra were compared with spectra from known pigments to identify the chemical compounds. Together, these techniques identified several pigments on the sculpture: red ocher, vermilion, orpiment (yellow), and indigo. A selection of samples was embedded in resin as cross-sections, preserving the stratigraphy of clay, ground, and paint layers for further study. Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) To continue the study of the sculpture’s pigments, Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) was used to investigate a red pigment sample from the neck in greater detail. The mounted cross-section was analyzed to examine stratigraphy and elemental composition at high resolution. In the red pigment sample, the upper layer corresponds to the painted surface, with clay visible beneath. The elemental mapping identified lead and iron in the surface layer. XRF, FTIR, Raman, and SEM-EDS were used to provide complementary evidence for the red pigment on the neck: XRF detected iron and lead; FTIR suggested ocher with kaolin, quartz, and calcite; Raman identified hematite; and SEM-EDS confirmed iron- and lead-containing compounds. Taken together, these analyses identify the pigment as red ocher containing hematite. New Insights and Future Study This study aimed to understand how Headless Seated Figure was made and what materials were used internally and externally. X-radiography and micro-CT scanning revealed that the clay was hand modeled around an internal wooden support and the figure was built up by multiple layers of clay. XRF, FTIR, Raman, and SEM-EDS identified the pigments across the small figure. The project illustrates the range of analytical and imaging techniques we use in the Straus Center to investigate how an object was made and the materials used to create it. Although the Khara Khoto objects now dispersed across a small number of museum collections were unethically removed during early 20th-century expeditions, technical study plays an important role in understanding and responsibly caring for them today. By combining close visual examination and scientific analysis, this technical study project contributes new insight into the materials and making practices of Khara Khoto while supporting future scholarship, stewardship, and exhibition. A selection of objects from Khara Khoto in our collections will appear in the exhibition Elements of Chinese Art: Materials and Making at the Harvard Art Museums in Spring 2027. I wish to thank Sarah Laursen, Katherine Eremin, Georgina Rayner, and senior conservator of objects and sculpture Angela Chang for their support of this project, as well as the Collections Management staff who assisted with object transport throughout my research. Kaela Nurmi is the objects conservation fellow (2024–26) in the Straus Center for Conservation and Technical Studies at the Harvard Art Museums. [1] M. B. Piotrovskiĭ, Lost Empire of the Silk Road: Buddhist Art from Khara Khoto (X–XIIIth Century) (Milan: Electa; Thyssen-Bornemisza Foundation, 1993), 54. [2] Francesca G. Bewer, A Laboratory for Art: Harvard’s Fogg Museum and the Emergence of Conservation in America, 1900–1950 (Cambridge, Mass.: Harvard Art Museums, 2010), 114.