Proteomic identification of organic additives in the mortars of ancient Chinese wooden buildings†
Mortars are the layers paved on the surface of timber, earth or stone before painting and drawing. The analysis of their material composition and manufacture technology is necessary for revealing old technological approaches, selecting a suitable technological process in restoration and protection, and guiding the development of traditional technology of Chinese painting and colored drawings. According to ancient literature, crop flour and blood have been used as binders in the mortars of Chinese wooden buildings. However, little work is published on their scientific identification, and the reported methods could not determine their precise origins, which is important to understanding ancient mortar technology. In this study, Fourier Transform Infrared Spectroscopy (FTIR), Liquid Chromatography Tandem Mass Spectrometry (LC/MS/MS) and starch grain analysis were employed to analyze the three mortars taken from the Old Summer Palace (18th and early 19th centuries), the Eastern Royal Tombs of the Qing Dynasty (middle 17th to early 20th centuries) and the Taiyuan Confucius Temple (late 19th century), respectively. FTIR analysis indicated the presence of proteins, and then different organic additives, namely, wheaten flour, cattle blood and pig blood, were identified respectively in the three mortars by LC/MS/MS analysis. Starch grain analysis also confirmed the proteomic results. Thus, proteomic analysis is highly effective for identifying the nature and origin of organic additives in the mortars of ancient painting.