Identification and tentative removal of collagen glue in Palaeolithic worked bone objects: implications for ZooMS and radiocarbon dating

Collagen glue has been used for nearly two centuries to consolidate bone material, although its
prevalence in museum collections is only now becoming visible. Identifying and removing collagen
glue is crucial before the execution of any geochemical or molecular analyses. Palaeolithic bone
objects from old excavations intended for radiocarbon dating were first analysed using ZooMS
(Zooarchaeology by Mass Spectrometry) to identify the animal species, however peaks characteristic
of both cattle and whale were discovered. Two extraction methods for ZooMS were tested to identify
the authentic animal species of these objects, which revealed that these were originally whale bone
objects that had been consolidated with cattle collagen glue. This is the first time animal collagen glue
has been identified in archaeological remains with ZooMS, illustrating again the incredible versatility
of this technique. Another technique, Fourier Transform Infrared Spectroscopy in Attenuated Total
Reflectance mode (FTIR-ATR), was also tested if it could rapidly identify the presence of collagen
glue in archaeological bone material, which was not the case. Two other cleaning methods were
tested to remove bone glue contamination prior to radiocarbon dating, along with two modified
collagen extraction methods for ZooMS. These methods were applied to bone blank samples
(FmC = 0.0031 ± 0.0002, (n = 219), 47 336 ± 277 yr BP) that were experimentally consolidated with
collagen glue and to the Palaeolithic bone material (ca. 15 000 and 12 000 yr BP). The experimental
bone blanks produced excellent 14C ages, suggesting the cleaning methods were successful, however
the 14C ages for some of the Palaeolithic material remained too young considering their contextual
age, suggesting that the collagen glue contamination had most likely cross-linked to the authentic
collagen molecule. More research is needed in order to gain a deeper understanding of the occurrence
and elimination of cross-linked collagen-based glues in material from museum collections.