Xiaohe (Chine): Proteomics reveals bovine origin of 3500-year-old glue
Adhesives may not sound the most exciting of substances but they can give clues as to how people lived throughout the ages. With a myriad of applications such as toolmaking, building, pottery repair, painting and lacquers, adhesives made from plant resins and gums, animal bones, blood and egg have been identified in historical and archaeological items dated over thousands of years. The oldest report to date is the use of animal glue in ancient Egypt about 8000 years ago.
Due to their organic nature, adhesives and glue degrade over time, making it difficult to identify them. However, chromatographic and mass spectrometric techniques have been used to good effect, as well as proteomics methods which have revealed the presence of animal glue, egg white and yolk and milk casein.
It was proteomics that Chinese researchers turned to when they analysed the adhesive on an ancient wooden staff inlaid with bone found in the tomb of a suspected shaman in the Xiaohe cemetery in northwest China that dated from 1980-1450 BC. This rare opportunity to examine a prehistoric adhesive was given to Yimin Yang and colleagues from the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, the University of Chinese Academy of Sciences, Beijing, and the Xinjiang Cultural Relics and Archaeology Institute, Ürümchi.
Wooden staffs inlaid with bone
A total of 167 graves were uncovered in this cemetery and the staffs were consistently found standing at the head and foot of the mummified bodies. They were made from wooden poles with inlaid bone along one vertical section and were decorated with hair and twigs.
The staff that was chosen for analysis was incomplete and the bone had become detached, exposing the adhesive beneath, so no extra damage had to be inflicted to gain access. The yellow, semi-transparent adhesive was analysed first by FTIR spectroscopy, which indicated that the substance contained some type of protein, based on the positions of the N-H, C=O and C-N absorptions.
The proteins were extracted from the material and separated by gel electrophoresis, producing one long smeared band down the gel, which is a common occurrence in archaeological samples. This band was cut into pieces that were pooled to digest the proteins for LC/MS/MS analysis of the resulting peptides.
In database matching, 12 peptides were identified from bovine collagen α1 type I and 6 from collagen α2 type I, showing that collagen was present in the adhesive. This was confirmed by searching against a bovine-specific database, which identified these aforementioned 18 collagen peptides as well as 62 others.
The discovery that the adhesive was made from cattle is consistent with the reliance of the Xiaohe people on cattle, a fact reinforced by earlier archaeological examinations. They were used as food and to provide milk, leather, bow strings and fertiliser and now we know that the animal leftovers were used to make glue.
Until this investigation, the earliest known use of animal adhesive in China was about 3000 years ago but now we can predate that by another 500 years. Glues made from deer, horse, cattle, mouse, fish and rhinoceros have been recorded in China but the cattle glue from Xiaohe takes the date back to at least 1450 BC when the cemetery was known to be in use.
Journal of Archaeological Science 2015, 53, 148-155: "Proteomic identification of adhesive on a bone sculpture-inlaid wooden artifact from the Xiaohe Cemetery, Xinjiang, China"