Analytical Protocol for Detecting Organic Materials

From a search of the available literature, the project team found that a number of analytical procedures have been published for characterizing either Asian or European lacquer. However, there are several reasons an ideal analytical procedure should be applicable to the widest possible range of both Asian and European materials.

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Fundamentally, it is not necessarily obvious from visual observations alone which type of lacquer is present on a piece of furniture. Many japanning techniques produced excellent, high-quality imitations of Asian lacquer. The project team also found that in many of the published procedures, only major components in the lacquers could be identified, yet knowledge of minor components is also important because they may affect the appearance and stability of lacquer. Finally, one must always take into consideration that unusual materials not described in published recipes and formulations may be present.

Application of a single test method would streamline the analytical process and ensure that a minimum of sample material would efficiently yield a maximum of information. The project team set out to develop such a testing method.

Pyrolysis gas chromatography/mass spectrometry using tetramethylammonium hydroxide for derivatization (TMAH-Py-GC/MS) proved to be the best overall method for characterizing lacquers of both types of origin. The test results from TMAH-Py-GC/MS were processed using a calibration table to automatically detect all known chemical compounds from the two types of lacquer. Presently, the table holds the names, retention time data and significant ions from the mass spectra of nearly 300 compounds. Systematic detection of all of the marker compounds in every sample tested is, without doubt, the single greatest advantage of using the calibration table to process the data.

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The procedure works well on intractable materials. It possesses sufficient sensitivity to detect minor and trace components, materials from conservation treatments are capable of detection, and it can identify materials from Asian and European lacquer formulations even if they are aged. TMAH had the minor drawback of producing multiple derivatives of the substituted catechols in Asian tree saps. This limitation was overcome by tabulating the peak area results for all derivatives formed from each catechols compound.

Minimizing the amount of sample required for testing remains an active area of research. It is difficult to obtain an adequate amount of sample either from lacquered objects with pristine surfaces, or from those that that lack removable attachments (such as the gilded mounts on the JPGM furniture), because the sampled area would be unacceptably large. Research continues on finding ways to modify the TMAH-Py-GC/MS procedure to accommodate smaller samples. Presently, small samples are best analyzed using Fourier-transform infrared spectrometry with reference spectra databases (FTIR). This technique can identify major components in lacquers and is good for identifying nitrocellulose and other modern synthetic materials, but is incapable of differentiating the three Anacard tree saps.

The complete analytical protocol is available for downloading in PDF (1 page, 57KB).

Page updated: September 2010