Ancient Bones Characterization and Preparation Through Freeze-Drying Process

Ancient bones, presumably dating back to 6000 BC and 1500 BC, have been characterized employing different physical analyses (optical and electron microscopy, characteristic X-ray fluorescence, and others) and prepared to be submitted to further investigations by nuclear techniques for dating analysis. Particular attention has been devoted to the freeze-drying process (also known as lyophilization) of the biological samples, which is based on the tissues drying under frozen environment, enabling removal of water and absorbed gases. Such a process presents different advantages, such as the possibility to store the samples at room temperature preserving their chemical properties, and the enhancement of the weight concentration of elements in the matrix. In this work attention is devoted to freeze-drying of cortical and trabecular bones, which loss water slowly with respect to soft tissues. The essential parameters to control during the process are the temperature and the pressure, the maintenance of a low gas pressure and the drying time, allowing the proper ice sublimation and the water degassing from the sample. The aim of the presented work is that to describe the lyophilization of cortical bones, to freeze and subsequently store the sample at low pressure, sublimating the ice on their surface and eliminating the gas under vacuum conditions. Experimental measures were performed to reduce the water content in the range of 1–5 wt.%. Measurements of water desorption, electronic microscopy before and after their treatment process, as well as Raman and FTIR spectroscopy were performed on the treated samples. The described procedure allows to prepare samples at high carbon concentration from which, employing nuclear analysis, it is possible to evaluate the content of stable isotopes and of radiocarbon, which have a crucial relevance for dating of biological samples.