Painted wooden coffins, characteristic funerary boxes with decorative paintings, are found in the Mediterranean and East Asia. In Egypt, their use spanned from the Old Kingdom to the New Kingdom. In China, they appeared during the Han Dynasty, with examples from the Warring States period being among the earliest. The practice continued through the Han Dynasty and into the Wei and Jin Dynasties, even spreading to the Hexi Corridor. The Xianbei people adopted the practice, integrating it into their burial customs. Studies of Egyptian painted wooden coffins have utilized a combination of non-invasive and micro-invasive analytical techniques, leading to the creation of pigment libraries. In contrast, studies of Chinese painted wooden coffins have largely focused on the imagery, with limited scientific analysis of materials and techniques. Previous studies often required large sample sizes. This research addresses this gap by using a multi-analytical approach with minimized sampling on coffin planks from a Northern Wei tomb in Shanxi, China, to determine the pigments used and the painting process, supporting conservation and historical art research.

Existing research on Egyptian painted wooden coffins showcases advanced analytical methodologies combining non-invasive (multispectral imaging, infrared spectroscopy, Raman spectroscopy) and micro-invasive techniques. These studies have led to pigment identification and characterization of materials, contributing to chronological frameworks. In contrast, studies on Chinese painted wooden coffins, primarily from the Han and Jin Dynasties in the Hexi and Xinjiang regions, have concentrated on iconographic interpretations, largely neglecting material analysis. While some analyses of pigments have been conducted, they typically involve larger sample extractions, potentially harming the artifacts. This paper addresses this deficiency by employing a less invasive approach and a broader range of analytical tools, drawing comparisons to existing methodologies applied to both Eastern and Western examples.

This study employed a multi-stage analytical approach, combining non-invasive and minimally invasive techniques. Initially, in situ non-invasive analyses were performed on three coffin planks using portable X-ray fluorescence (p-XRF) spectroscopy, portable micro-Raman spectroscopy (p-RS), and fiber-optic reflectance spectroscopy (FORS) to identify pigment locations and compositions. Twenty to twenty-three test points per plank were analyzed with these techniques. Subsequently, four micro-samples (<3 mm) were carefully extracted from the edges or damaged areas for detailed laboratory analysis. These samples underwent optical microscopy (OM) to observe the layering and morphology of the pigments. Scanning electron microscopy – energy dispersive spectroscopy (SEM-EDS) provided elemental composition data. Confocal micro-Raman spectroscopy (micro-RS) offered molecular structural information of the pigments. Finally, simulated samples were prepared to corroborate the findings from the micro-samples. Specific instrumental settings, such as laser wavelengths, acquisition times, and spectral ranges, are detailed in the original paper.

Cross-sectional analysis revealed a yellow primer layer (pararealgar) beneath the painted layers. Six main colors were identified: red (cinnabar, HgS), yellow (pararealgar, As4S4), green (orpiment and indigo mixture), blue (indigo and lead white mixture), white (gypsum, CaSO4), and black (carbon black, C). The p-RS and p-XRF analyses provided initial identification of the pigments at multiple test points on the coffin planks. Micro-RS and SEM-EDS analyses confirmed these identifications and showed the specific composition of the mixed green and blue pigments. The green pigment was confirmed as a mixture of orpiment (As2S3) and indigo, while the blue pigment consisted of indigo and lead white. The use of a pararealgar primer layer suggests a specific painting technique used during the Northern Wei dynasty. Some areas had three layers of paint, while most only contained two. The combination of organic dyes with inorganic pigments for color enhancement is notable.

The findings significantly advance our understanding of Northern Wei Dynasty painting techniques. The use of a yellow primer layer and the specific pigment combinations, particularly the mixture of organic and inorganic pigments for green and blue, highlight the sophistication of the techniques employed. These findings contrast with previous studies that lacked a comprehensive, multi-analytical approach. The minimized sample size represents a significant advancement in the field, preserving the artifacts while maximizing information gained. The identified pigments are consistent with those used during this period in other regions but reveal the unique characteristics of this particular example. The combination of in-situ and lab-based analyses provides a more complete and reliable understanding of the artifacts than either method alone.

This study provides a detailed and accurate characterization of the pigments and painting techniques used on Northern Wei Dynasty coffin planks from Shanxi. The multi-analytical approach combined in-situ non-invasive techniques with minimally invasive analysis of micro-samples. The findings showcase the advanced technological skills and knowledge of pigments during the Northern Wei dynasty. This research provides essential knowledge for the informed conservation and restoration of these artifacts. Future studies could extend this approach to other similarly aged artifacts to create a more comprehensive understanding of pigment use and artistic techniques throughout China during this historical period.

The study was limited to three coffin planks from a single tomb. While the findings are significant, they might not be fully representative of all Northern Wei Dynasty coffin paintings. The minimal sampling strategy, while advantageous for preservation, limited the amount of material available for analysis in each location. The interpretation of some of the Raman spectra was complicated by fluorescence interference, particularly in the case of the blue pigment. Further research could address these limitations by extending the analysis to additional artifacts from various Northern Wei sites and refine the analytical techniques to mitigate fluorescence interference.