Asian Organic Colorants

New findings on traditional Asian organic colorants, including a strategy for analysis and databases for professionals

Category
- Conservation
Years 2006 – 2010
Status
- Completed
Organizer
- Getty Conservation Institute

About

Goal

The Asian Organic Colorants project sought to develop a strategy for analysis of traditional Chinese organic colorants used as textile dyes and organic pigments in Chinese wall paintings and for analysis of organic colorants used as textile dyes and organic pigments in Asia. Detection and identification of these has long been challenging, as many of the biological sources used to create them have not been well studied and the organic paints concentrations are low.

Outcomes

Library of Ultraviolet-Visual (UV-Vis) spectra for color-contributing components
Electro-Spray Ionization—Negative Ion Mode (ESI-NIM) mass spectra database of the same diagnostic components of organic colorants including both MS and MS-MS spectra

Background

Not only have the biological sources used to create traditional Chinese organic colorants not been well studied but, in the case of organic paints, concentrations of these colorants are low compared with inorganic pigments and binding media. Much less is known of these colorants than of their European and American counterparts.

In previous work by the Conservation Institute at the Mogao Grottoes in Dunhuang, China, for example, determining specific organic colorants used in the caves proved challenging because the biological sources used to produce the dyes and pigments were frequently unique to the geographic region, and the reference samples required for identification were not available.
The biological sources used to produce organic colorants in Asia, specifically China, were acquired and used to prepare reference samples. These samples were prepared as dyed wool and silk and as pigments. Paints were prepared from the organic pigments and were applied to wall painting mock-ups.

From these analyses, the project team created analytical databases and disseminated this information to the conservation community. Analytical techniques were evaluated on the wall painting mock-ups to determine their diagnostic value for the detection and identification of Asian organic colorants. An analytical strategy was developed to identify Asian organic colorants and applied to historic samples selected from the Mogao Grottoes.
A review of published literature determined that 115 biological sources were used to produce organic colorants in the Mogao Grottoes wall paintings. Based on the frequency of independent citations, twenty-four biological sources were selected for study, most of which were identified at the species level. For those cited only at the genus level, species were selected that were most likely to be available in the region based on botanical references and on discussions with a botanist at Beijing University. In addition to biological sources and recipe data, painting techniques and historical context were collected.
Additional project assistance provided by:

J. Paul Getty Museum Preparations Department: Bruce Metro, Rita Gomez, and Cary Stehle

Courtauld Institute of Art, Conservation of Wall Painting Department, University of London: Lisa Shekede, Sharon Cather, Stephen Rickerby, Charlotte Martin, Sibylla Tringham, and Giovanni Verri

Huntington Library, Art Museum, and Botanical Gardens: Kathy Musial and Katarina Eriksson