Molecular characterization of animal glues for the purpose of restoration treatments

Abstract

Abstract: Several thousand years ago, mankind perceived the gap and the need for an adhesive in order to make complicated objects consisting of two or more different or even same materials. Among all the materials that have been used throughout history, animal glue has been employed as an adhesive for several various tasks and still has kept its application. Animal glue has been used in book binding, painting binders, furniture manufacturing, to name but a few. Today, in cultural heritage field, it is being used as adhesive in restoration treatments. It is of great importance for conservators to be confident in their knowledge of the original materials they are using and introducing to the ‘matrix’ of cultural heritage objects in order to make proper decision in the process of restoration. Animal glues, however, are intrinsically challenging materials due to the fact that different animals’ collagen proteins exhibit different behaviors or performances due to their different origin or preparation processes. Accordingly, different animal glues are used for different tasks. Therefore, it is critical for conservators to know the composing materials of animal glues they employ. In this thesis, collagen proteins of several samples of animal glue which have been provided by restoration laboratories of both S. Orsola Benincasa, Naples, Italy and Museo del Prado, Madrid, Spain were identified by MALDI-TOF and LC-MS/MS coupled with Mascot bioinformatic tool with the goal of protein identification. Samples of S. Orsola Benincasa were analyzed by LC-MS/MS and Mascot in order to identify the specie(s) and tissue(s) they have been made of. Out of 8 samples, only one of them was made of what the label claimed to be. These results showed the importance of these experiments for the art conservation community as using known and standard materials forms a great part of their actions toward restoration of cultural heritage objects. Additionally, one of the samples, rabbit glue totten sixties, were chosen to demonstrate, in a preliminary manner, the capabilities of proteomics in the evaluation of degradation phenomenon. Samples of Museo del Prado were analyzed by MALDI-TOF in order to demonstrate differences between the amount of information one can gain from MALDITOF in comparison with LC-MS/MS. Finally, one of the samples of Museo del Prado was used to improve the sample preparation protocol, by examining the hypothesis of whether or not combining two protocols could yield higher sequence coverage and betterquality spectra. Results of the series of experiments showed that adding ZipTip clean-up step after StageTip protocol increases the number of peptides in respect to what can be obtained by using a single chromatographic step.