Lacquered objects are among the most highly treasured works of Asian art. Multiple, complex layers of lacquer are used to decorate the surfaces of screens, boxes, dishes, cabinets and small objects imparting a distinctive appearance that is also pleasantly tactile. With a history of production in Japan and China dating back to 5000 BCE, lacquerware began to be exported to Europe in the mid-16th century, where such objects were desired due to their uniqueness and great beauty. In the 17th century, European craftsmen began integrating panels removed from Asian lacquered screens into new pieces of furniture, which were then completed with panels that imitated the look and motifs of Asian lacquer, albeit using radically different materials and techniques. These European imitation lacquer techniques have been referred to as japanning.
The Characterization of Asian and European Lacquers project aims to develop a comprehensive analytical method to identify organic materials present in Asian and European lacquers.
Compositional and technological differences between Asian and European lacquers affect their aging behavior and long-term stability, which ultimately impact the lacquers' conservation. Scientific analysis of these lacquers could provide conservators with vital information about the composition and condition of the lacquer layers, aiding in the development of appropriate conservation treatments.
In response to these needs, scientists from the Getty Conservation Institute collaborated with J. Paul Getty Museum conservators to develop a methodology for sampling and analysis of the organic components of Asian lacquers and their European imitations that improves upon existing techniques both in terms of sensitivity and range of detectable compounds. Nine pieces of mid-18th century French furniture from the J. Paul Getty Museum that incorporate panels of Asian lacquer as part of their surface decoration served as case studies.
Research of the Characterization of Asian and European Lacquers project is divided into several components:
- Development of a protocol for sampling individual lacquer layers
- Development of an analytical protocol for detecting organic materials
- Acquisition and analysis of reference materials
- Study of Asian lacquered objects from the Getty Museum and other institutions
- Compilation and evaluation of test data on European imitation lacquers.
In addition to aiding in the development of appropriate conservation treatments, the technical data from these case studies will be included among the information on these pieces in the forthcoming catalog of the Gettys permanent collection.
The project began with a methodical literature review to determine the list of possible constituents for both European and Asian lacquers of the 18th century. For European materials, primarily 17th and 18th century sources were consulted; however, for Asian techniques, we were forced to rely on 20th century texts in the hope that they accurately describe traditional techniques as practiced in prior centuries. It is worth noting that much of the Asian lacquer used in French furniture was made specifically for export, using techniques that varied from those used for higher quality domestic production. Therefore, modern descriptions of traditional techniques may not be representative of the materials in this study.
From our search of available literature we able to draw the following conclusions:
Asian lacquers consist largely of the sap from several trees within the Anacardiaceae family that grow throughout a number of specific geographical regions within Asia. The traditional lacquer known as urushi in Japan and qi in China is made from the sap of Toxicodendron vernicifluum. Vietnamese and Taiwanese lacquer is composed of laccol sap from Toxicodendron succedaneum. Burmese and Thai lacquer is composed of thitsiol sap from Gluta usitata. The three types of tree sap, composed mainly of substituted catechols which have long unsaturated side-chains, are toxic skin irritants.
Some form of pretreatment is required in order to convert the raw tree saps to a material suitable for application. For example, Kurome lacquer, the starting material in many Asian lacquer preparations, is prepared by heating and stirring the tree saps to reduce the initial water content to a low level. The working properties, appearance and cost of the formulations are modified by adding other organic materials to the Kurome lacquer such as drying oils, persimmon juice, shellac, animal glue, wood oil, benzoin and starch. Color is imparted by adding mineral and/or organic pigments. Each individual coat of Asian lacquer is cured first at high humidity (activated by a naturally-occurring enzyme) followed by air-drying. Lacquers on objects are built of multiple layers, often more than twenty.
In contrast, European japanning methods utilize varnishes that are highly complex mixtures of resins and oils, some of which may be present in small amounts. A few such products are resins from trees (colophony, sandarac, hard and soft copals, and elemi) and insects (shellac), along with organic colorants such as dragon's blood and gamboge. The materials are dissolved in an organic solvent and applied to the object, and the dry lacquer layer forms mainly by solvent evaporation, although lacquers with added drying oils require a certain amount of curing before a topcoat can be applied.
Analyzing Asian and European Lacquers
Successful characterization of these lacquers requires an analytical procedure capable of detecting even minor quantities of as many of the constituents as possible. Although separate procedures have been published for gas chromatographic analysis of Asian lacquer and of complex European furniture varnishes, the project teams desire is to develop a single analytical method capable of identifying and differentiating the components of both types of lacquer in one sample. This approach would streamline the analytical process and ensure that a minimum of sample material would efficiently yield a maximum of information.
One factor that limits the number of potential analytical tools for characterizing Asian lacquers is that the films are extremely intractable, being nearly impossible to dissolve in any type of solvent. Thus, the analysis must be carried out directly on the solid sample material. Pyrolysis-gas chromatography/mass spectrometry using derivatization with tetramethylammonium hydroxide (TMAH-Py-GC/MS) is the primary analytical method used. Heat and the TMAH reagent are used to degrade the intractable lacquer into small marker compounds that are characteristic of the original organic materials.
Presently, this technique requires approximately 50-100 micrograms of sample material for analysis, but the project team is conducting research to reduce the sample requirements. To test smaller samples, Fourier-transform infrared spectrometry (FTIR) is used and identification is done by matching the unknown spectrum to reference spectra of known materials.
Last updated: September 2010