Scientific Studies of Pigments in Chinese Paintings
Edited by Blythe McCarthy and Jennifer Giaccai
Scientific Studies of Pigments in Chinese Paintings explores the pigments used in Chinese paintings on silk and paper from the Song dynasty (960–1279) through the early twentieth century. The first book on this subject to bring together information gathered from a large group of works—over two hundred—it provides physical proof of both when and how pigments were used. The team of scientists examined works from the Freer Gallery of Art and Arthur M. Sackler Gallery collections, including scholar-paintings of several genres as well as portraits. Detailed analysis of the introduction and use of imported colorants, including cochineal, a dye indigenous to the Americas, and Prussian blue, a synthetic pigment first made in Germany in 1704, reveals that these and other imported pigments were introduced into the palette in the eighteenth and nineteenth centuries primarily by professional painters. Greatly expanding the available information in this area of study, this book enables a broader understanding of the materials and methods used by Chinese painters and provides a resource for scholars of Asian arts and cultures.
As part of a multi-year project supporting the catalogue, Jades for Life and Death, the scientific research team has been identifying the minerals of the jades in the collections of the Freer|Sackler. Reflectance spectroscopy has proven to be a valuable tool for the speedy characterization of most jade materials. Further research will compare the mineral content, object appearance and history.
Yellow organic colorants
Among organic colorants, yellows have a high rate of fading from light exposure. Among yellow pigments, gamboge resin and “zumi”, which originates from the bark of certain crabapple trees, were commonly used in Japanese printmaking . Chemical analysis of commercial pigments and raw plant materials collected in South and Southeast Asia, is being conducted to form references which can be used to better understand the materials in Japanese paintings and prints and their behavior under light.
Materials and structure of lacquers
Asian lacquer is composed of many layers, each with a specific composition and containing various additives. Research on the lacquers in the museum collections is identifying the materials used to form lacquers , the types of additives incorporated and the structure of the lacquer itself.
Coatings on Japanese Metalwork
To protect the unique patina of a metal surface, artists may apply a coating, such as polymers or waxes, to inhibit corrosion. Over time, these organic coatings may exhibit different forms of deterioration (discoloring, hazing, and roughening). Research exploring the proper care of these objects includes understanding the ways different coatings age, their effectiveness of protecting the metal surface, and the ease of removability/replacement of the coating without damaging the patina.
Conservation practice can require the use of consolidants to stabilize materials (for instance, a flaking painted surface). The choice of consolidant will depend on the nature of the object and the treatment needs. An investigation into the use of polyvinyl butyral polymers examines the changes that occur over time with light exposure. Polymer color, oxidation, weight loss, cracking and removability have been monitored and compared to other conservation consolidants.
Carbon based inks
Carbon based ink is used in paintings throughout Asia. Ongoing research into soot formation and ink sticks, in collaboration with researchers from George Washington University, is a first step towards understanding and differentiating different types of black ink and pigments.
Research on Chinese pigments
A multi-year project to identify pigments used in Chinese paintings in the Freer|Sackler collections was undertaken to better understand the introduction of new pigments in later centuries. Much of the work in this project was carried out under a Mellon grant that supported the study of organic pigments in Asian art.
Egyptian Glass at the Freer Gallery of Art
In 1909, Charles Lang Freer bought a collection of 1,388 ancient glass beads, vessels, and mosaic fragments in Cairo, Egypt. Until 2013, the collection was largely left unstudied and was inappropriately stored. As a result, the Freer|Sackler Department of Conservation and Scientific Research is rehousing and researching the collection. This poster, presented at the American Institute for Conservation of Historic and Artistic Works Annual Meeting in May 2015, focuses on the storage project, the challenges associated with rehousing a large collection of small objects, and historical and technical research.
The so-called ‘Indo-Persian’ carpets
International trade and political stability in 16th-century Iran gave rise to new economic developments, including textile production. The new Safavid rulers saw this moment as the ideal opportunity to develop the Iranian carpet industry to respond to the demands and competitiveness of the international market. Aiming to look at this transformation during the 16th and 17th centuries, this project takes an interdisciplinary approach involving material science, art history and history to the study of these carpets from Portuguese and USA collections. The results will contribute to a better understanding of the impact of the new overseas trade networks in the development of one of the great forms of artistic expression in Iran.
Raquel Santos presented at the 43rd annual meeting of the American Institute for Conservation of Historic and Artistic Works. view poster (PDF)
Persian minai ceramics
Persian minai ceramics produced during the late twelfth and early thirteenth centuries are decorated with multicolored enamel overglazes and gilding on an opaque white ground. These ceramics are often referred to as haft-rang, or “seven-colored,” due to the use of black, red, blue, turquoise, green, purple, brown, and white glazes, which create remarkably detailed objects adorned with figural and geometric designs. Analysis of the materials and techniques of these ceramics is underway.
Chinese Buddhist stone sculpture
Scientific research on the materials used in Chinese Buddhist stone sculpture is currently in progress. This study will illuminate the types of limestone and sandstone used for carving at some of the major Buddhist temple cave sites in Shanxi, Hebei, and Henan provinces dating from the Northern Wei to the Northern Qi dynasties, including North and South Xiangtangshan, Yungang, Longmen, Gongyi, and Tianlongshan. Analytical methods are being used to compare the materials of sculptures from the Freer Gallery’s collection with those from temple cave sites. The results, correlated with previous art-historical attributions, will allow the sculptures to be assigned to specific cave sites of origin. This project will aid research on the Freer Gallery’s collection—especially in light of the upcoming exhibition on the temple caves of Xiangtangshan—as well as create a framework for the study of Buddhist stone sculpture in other Western museum collections.
Central Asian ikat textiles
Ikats from Central Asia were typically dyed with natural materials found in insects and plants, such as cochineal, madder, and indigo. Because most of the sixty-five ikat textiles in the Freer and Sackler’s collection are from the nineteenth and twentieth centuries, however, care must be taken to not overlook the use of available synthetic dyes. Fourier transform infrared spectroscopy, high performance liquid chromatography, and UV-Visible spectroscopy are being used to differentiate and identify the synthetic and/or natural dyes found in the collection’s ikat textiles. The information collected will be used by conservators during repair and restoration to ensure the same mixture of colorants is used as those incorporated by the artist.
Synthetics such as aniline dyes were invented and developed in the mid-nineteenth century, and may have been incorporated into works of art to reduce costs, improve color fastness or consistency, or to access new shades. The analytical data on ikat silks of the nineteenth century will also be used to track the movement of synthetic dyes from Europe into East Asia.
Chinese cinnabar and vermilion
Both natural (cinnabar) and synthetic (vermilion) forms of the red pigment mercury II sulfide, HgS, are known to have been used in China, where the pigment occurs widely in archaeological contexts. The existence of impurities or differences in the particle size have been used to differentiate the Chinese dry-process of manufacturing and natural cinnabar, but this method is not always successful due to inclusion of grinding or size classification steps, or the presence of contaminants in processed vermilion. In this study to determine differences between natural and synthetic forms of the pigment, several samples were analyzed using isotope ratio mass spectrometry (IRMS) at the Smithsonian Stable Isotope Mass Spec Laboratory. Studies of trace elements in the samples are underway using x-ray fluorescence spectroscopy (XRF) and electron microprobe at the Smithsonian National Museum of Natural History, as well as Raman spectroscopy at the Smithsonian Museum Conservation Institute. The goal of the research is to develop a method that will discriminate between the two forms of the pigment, and possibly identify geological sources of mercury sulfide given sufficient analyses of raw materials.
Khmer stone sculpture
Beside stylistic and iconographic studies, petrographic analysis is a fruitful approach to studying Khmer stone sculpture and the sandstone materials with which they are composed. A petrographic classification of sandstones used by the Khmers for sculptural purposes would be a helpful tool for archaeologists, museum curators, and others interested in pursuing research on early stone usage, geologic source, and provenance. Collaborative research is underway to pursue creating such a classification, conducted within the context of our current knowledge about regional geology and ancient quarrying in Cambodia. Petrographic study includes freestanding sculpture of pre-Angkor, Koh Ker, and Bayon styles, as well as the special variety of sculptural arts represented in architectural decorative lintels. The large data set on stone materials offers invaluable support to current archaeological excavations in Southeast Asia.
Together, the ancient Chinese jade collections of the Freer and Sackler Galleries and the Art Institute of Chicago (AIC) comprise an unusually large and extraordinary group of these objects in the West. Through a collaborative project with the AIC and Northwestern University, an integrated analytical approach has been chosen for the characterization of Chinese jades composed of nephrite. Samples, encompassing both geological reference specimens and museum objects, were studied to understand the characteristics of natural color variations induced by cationic substitutions, as well as human-induced alteration such as heating. Non-invasive methods of analysis were employed, including x-ray fluorescence spectroscopy, Raman microspectroscopy, visible reflectance spectroscopy, and x-ray diffraction. A related project focused on the textile ghosts on archaeological jades left from degraded silk fabric that had been in contact with jades in the burial environment.
Identification of Turquoise Inlay
The semi-precious stone inlay on forty-four Chinese belt hooks from the Warring States Period (5th -3rd c. BCE) was identified as part of technical study of the belt hooks. The belt hooks are part of the recently acquired Dr. Paul Singer Collection at the Arthur M. Sackler Gallery, Smithsonian Institution. Although most of the inlay appeared to be turquoise, under closer examination it became clear that some of the belt hooks had some or all of their inlay replaced. Traditional methods of turquoise identification, most commonly X-ray diffraction (XRD) or Fourier transform infrared spectroscopy (FT-IR), require sampling. However, the small size of the inlay pieces used in the belt hooks makes sampling problematic: a non-destructive identification method was desired. An evaluation of non-destructive methods for identifying turquoise was undertaken, identifying the inlay on ten belt hooks from the original study, as well as reference samples of turquoise and common turquoise substitutes. The distinctive reflectance spectrum of turquoise in the visible region showed the potential of fiber optic reflectance spectroscopy (FORS) for non-destructive identification of turquoise. Combined with X-ray fluorescence (XRF) and ultraviolet fluorescence, the three non-destructive techniques were able to successfully identify turquoise and other inlay materials on the belt hooks.
This work was presented at the 2003 American Institute for Conservation annual meeting. [pdf of poster for download here]