###### Abstract  
The present work reports the identification of inorganic and organic materials applied in gildings of Kizil Grottoes mural paintings, located in the western part of China. A total of 10 gold gilding samples were collected from caves dated in the fourth-seventh century AD. In this research, optical microscopy, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX), UV fluorescence microscopy, and pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) analyses were carried out to clarify the mordant materials and the coating materials on the foils. This research reports some new finds of the gilding technique in Kizil grottoes, such as oil and lac resin being used as mordant to provide a binding medium for gold gilding, gold powder probably being used as pigment, and some organic dyes being well preserved under gold foil. These interesting findings not only provide scientific evidence for us to understand the materials and techniques of gold gildings on Kizil Grottoes murals, but also illustrate material trade and technique exchanges along the Silk Road in the past.  
gilding; lac resin; organic materials; Kizil Grottoes +
Footnote †: journal: Applied  
0000-0002-4000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-00000-0000-0000-0000-00000-00000-00000-00000-0000  
Previous investigations about the painting materials in Kizil wall paintings were performed, and the main results were focused on the identification of inorganic pigments [4,5] and organic binder [6], which was determined as animal glue. [PERSON] [7,8] paid attention to the gilding material and technique in Kizil and found that lac resin was used as the red mordant (an adhesive material used in gilding) for gold gilding, while drying oil was applied for adhering tin gilding to the wall painting.  
Figure 1: (**a**) The location of Kizil grotoes and important ancient Buddhism grotoes along the silk road in China; (**b**) the front view of Kizil grotoes; (**c**) a mural painting in Kizil grotoes (Cave No. 171, fifth–seventh century AD).  
Considering the previous studies, a systematic investigation is still needed to reveal the gold gilding materials and techniques of Kizil's wall paintings. In addition, a noteworthy point from our previous investigation is that the gold foil was probably covered by another layer, which makes the golden luster not particularly obvious. We speculate that this may be related to the specific technique of gold gilding decoration. An upper layer applied on tin foil was reported in a wall painting of Bamiyan Afghanistan dated in the seventh century AD [9]. Most of this tin gilding showed a golden luster; this technique is called false gilding, which was also reported in medieval paintings in Western Europe [10; 11]. As for the layer applied on the gold gilding of Kizil, further research is necessary.  
In this context, this study focused on the gold gilding decorations in the murals of the Kizil Grottoes. Multiple analytical methods including optical microscopy (OM), UV fluorescence microscopy, scanning electron microscopy with an energy-dispersive X-ray analyzer (SEM-EDX), micro-Raman spectroscopy (\(\mu\)-RS), and pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) were carried out to systematically reveal the materials and techniques of gold gilding in Kizil.