Challenges in the data analysis of Asian lacquers from museum objects by pyrolysis gas chromatography/mass spectrometry

Identification of Asian lacquers in museum objects is a challenging task. Their identification by mass spectrometry is based on molecular marker recognition, and analysis of chromatographic profiles of several types of molecules. A summary of published markers and chromatographic profiles ‒ obtained with and without thermally assisted reactions (silylation and methylation) ‒ is included in this paper. Based on this, a decision-making scheme was established, and proposed to guide data interpretation. This method of data analysis was then applied to a group of lacquered objects belonging to the Asian art collection of the Museum of Zaragoza (Spain). Based on stylistic and art historical information, the objects are dated from the 16th to the 20th century and attributed to Japanese, Chinese, Burmese and Thai manufacture. Analytical pyrolysis with in situ silylation - gas chromatography coupled with mass spectrometry (Py(HMDS)-GC/MS) was used to analyse the lacquers, and scanning electron microscopy with energy-dispersive X-ray spectrometry (SEM-EDS) was used on cross sections to study the stratigraphy of the objects and understand the artistic techniques. The proposed scheme proved to be a useful analytical guide for the straightforward identification of the lacquer origin, even when this is present in mixture with other organic materials. In fact, a multi-faceted picture emerged, as some of the objects showed interesting mixtures of lacquers, such as urushi and thitsi, or unexpected compositions, which questioned their initial attributions. Complex or unexpectedly simple preparations and restoration treatments of the decorative surfaces were highlighted as well, supporting the museological investigation of these objects, in order to confirm/reject their authenticity and geographical provenance.