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Scientific analyses of the traditional materials and methods in thangka production are uncommon, as thangkas are sacred objects, the sampling of which is discouraged, in order to preserve their integrity. This study builds on this important ethical challenge and presents a three-stage methodology that systematically delves deeper into each layer of the composition, successfully enabling the investigation of different phases of production. In the first stage, visual examination of the painting, including observations under magnification, was used to assess its condition. In the next step, the infrared reflected (IRR) and short-wave infrared (SWIR) images revealed the underdrawing and instances of modifications as well as colour notations. Additionally, ultraviolet-induced visible luminescence (UVL), infrared-reflected false colour (IRRFC) and X-ray images provided important preliminary information on the colourants present, the nature of the underdrawing, and the painting technique. In the final stages, fibre optic reflectance (FORS), Fourier-transform infrared (FTIR) and Raman spectroscopies confirmed the identity of many of the pigments (cinnabar/vermillion, minium, iron oxide, malachite, azurite, indigo, Indian lac), the ground and the binder used for the blue and green paint layers. In addition, key details of practices and materials were revealed, that may indicate provenance or other information of scholarly importance. These will constitute a helpful comparison to existing and future studies of other thangkas.

Mount components and textile borders represent important elements of Asian paintings. However, they are often side-lined or not considered an integral part of the original piece, as they may be later additions or may have been replaced during historic conservation or mounting interventions. Nevertheless, evidence is sometimes present that textile borders are contemporaneous to the production of the paintings they frame or, in the case of paintings found in archaeological contexts, to the time of deposition. Even when not contemporaneous with the paintings, the mount textiles are often of significant historic interest in themselves, showing a range of complex textile techniques and materials, and highlighting the re-use of fabrics. In all these cases, the study and reconstruction of the original colours of the borders enable further understanding of the holistic visual impact originally intended for the composition, as well as of the role of colour itself, which was used to emphasise, complement or contrast important pictorial themes or motifs in the paintings. Furthermore, the identification of dyes and dyeing techniques has the potential to support the production date and provenance of the paintings. In this study, the textile borders and some additional mounting elements of six paintings (late 9th–10th century CE) from the Library Cave, Mogao Grottoes, Dunhuang, China, one rare Korean portrait painting dated 1789 CE, and two Tibetan thangkas (18th century) were investigated with the aim to identify the dyes present. Fibre optic reflectance spectroscopy (FORS) was used to obtain information non-invasively and, when sampling was possible, high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was used to obtain molecular identification of the dyestuffs employed in their production. Typical Asian dyes, such as gromwell (Lithospermum erythrorhizon), sappanwood (Biancaea sappan), safflower (Carthamus tinctorius), turmeric (Curcuma longa) and pagoda tree flower buds (Sophora japonica), were identified. Some of the dyeing techniques were commensurate with the geographical and temporal provenance assigned to these pieces. Considerations about fading and discolouration of the dyes enabled valuable additional information to be obtained that complements the evidence gleaned from the study of the paintings and informs conservators and curators on best practices in the preservation and display of these precious and delicate artworks.