Molecular and isotopic archaeology: Top grade tools to investigate organic archaeological materials

New Evidence on the Reliable Use of Stable Isotopes of Bitumen Fractions in Archaeological Research

One of the goals of archaeological studies is to determine how material goods and ideas moved among human populations, and bitumen is a worthy proxy because it has been used since prehistory. As a result, when bitumen is excavated from archaeological sites, determining its provenance is important because it sheds light on the trade and communication of populations at a given time. During the study of archaeological bitumen from coastal sites in central and southern Puglia (Italy), we observed that stable isotope ratios of saturated and aromatic fractions were incompatible with those obtained from asphaltenes, supporting the absorption of a foreign substance. Experiments showed that lipids are absorbed by bitumen and, in the case of oils, are distributed mainly in the saturated and aromatic fractions as their isotopic ratios change. The same experiments showed that the isotopic ratios of the asphaltenes do not change. Lipid absorption on the archaeological bitumen may have occurred before the bitumen was applied to the pottery, during the use of the pottery or while underground, before being excavated. These hypotheses are discussed, and it is concluded that the isotopic ratio of asphaltenes is a reliable proxy for provenance, whereas those of the saturated and aromatic fractions should be considered with caution due to possible lipid absorption. Nevertheless, they provide new information on pottery use that can be used in archaeological chemistry.

Biomolecular analyses enable new insights into ancient Egyptian embalming

The ability of the ancient Egyptians to preserve the human body through embalming has not only fascinated people since antiquity, but also has always raised the question of how this outstanding chemical and ritual process was practically achieved. Here we integrate archaeological, philological and organic residue analyses, shedding new light on the practice and economy of embalming in ancient Egypt. We analysed the organic contents of 31 ceramic vessels recovered from a 26th Dynasty embalming workshop at Saqqara^1,2. These vessels were labelled according to their content and/or use, enabling us to correlate organic substances with their Egyptian names and specific embalming practices. We identified specific mixtures of fragrant or antiseptic oils, tars and resins that were used to embalm the head and treat the wrappings using gas chromatography-mass spectrometry analyses. Our study of the Saqqara workshop extends interpretations from a micro-level analysis highlighting the socio-economic status of a tomb owner^3-7 to macro-level interpretations of the society. The identification of non-local organic substances enables the reconstruction of trade networks that provided ancient Egyptian embalmers with the substances required for mummification. This extensive demand for foreign products promoted trade both within the Mediterranean^8-10 (for example, Pistacia and conifer by-products) and with tropical forest regions (for example, dammar and elemi). Additionally, we show that at Saqqara, antiu and sefet-well known from ancient texts and usually translated as 'myrrh' or 'incense'^11-13 and 'a sacred oil'^13,14-refer to a coniferous oils-or-tars-based mixture and an unguent with plant additives, respectively.

Liquid chromatography and mass spectrometry for the analysis of acylglycerols in art and archeology

Lipid characterization in art and archeology, together with the study of lipid degradation processes, is an important research area in heritage science. Lipid-based materials have been used as food since ancient times, but also employed as illuminants and as ingredients in cosmetic, ritual, and pharmaceutical preparations. Both animal and plant lipids have also been processed to produce materials used in art and crafts, such as paint binders, varnishes, waterproofing agents, and coatings. Identifying the origin of the lipid materials is challenging when they are found in association with artistic historical objects. This is due to the inherent complex composition of lipids, their widespread occurrence, and the chemical alterations induced by ageing. The most common approach for lipid characterization in heritage objects entails profiling fatty acids by gas chromatography/mass spectrometry after saponification or transesterification. New developments in high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS) for the characterization of acylglycerols, together with more efficient sample treatments, have fostered the introduction of liquid chromatography for characterizing the lipid profile in heritage objects. This review reports the latest developments and applications of HPLC-MS for the characterization of lipid materials in the field of heritage science. We describe the various approaches for sample pretreatment and highlight the advantages and limitations of HPLC-MS in the analysis of paint and archeological samples. © 2020 John Wiley & Sons Ltd.

Analysis of balms taken from Egyptian human mummies using solid-phase extraction and gas chromatography-mass spectrometry

The aim of this paper is to establish a protocol by solid-phase extraction-gas chromatography-mass spectrometry leading to a wide and fine qualitative chemical characterization of the several natural substances present in human mummies' balms, using a minimal quantity of samples. In this study, nine samples were analyzed from mummies dating back from the Third Intermediate Period to the Roman Period, and were provided by the Confluences Museum (Lyon, France). Using solid-phase extraction, three fractions were examined in this protocol. The first one, eluted with hexane, concerned chemical families of hydrocarbons of bitumen. The second, eluted with ethanol, enabled terpenic compounds to be characterized and beeswax. The last one, composed of diethyl ether with 2% acetic acid, extracted carboxylic acids with a long aliphatic chain (fatty matter) and glycerides. This study also allowed the characterization of non-saponified compounds from beeswax to be obtained while excluding the common saponification step. The analyzed mummification balms were shown to contain fatty matter, beeswax, bitumen, and diterpenic resinous material. This one-pot solid-phase extraction-gas chromatography-mass spectrometry method was efficient in reducing both the number of analytical steps and the complexity of the archaeological balms subsequently analyzed by gas chromatography-mass spectrometry.

Analytical Approaches Based on Gas Chromatography Mass Spectrometry (GC/MS) to Study Organic Materials in Artworks and Archaeological Objects

Gas chromatography/mass spectrometry (GC/MS), after appropriate wet chemical sample pre-treatments or pyrolysis, is one of the most commonly adopted analytical techniques in the study of organic materials from cultural heritage objects. Organic materials in archaeological contexts, in classical art objects, or in modern and contemporary works of art may be the same or belong to the same classes, but can also vary considerably, often presenting different ageing pathways and chemical environments. This paper provides an overview of the literature published in the last 10 years on the research based on the use of GC/MS for the analysis of organic materials in artworks and archaeological objects. The latest progresses in advancing analytical approaches, characterising materials and understanding their degradation, and developing methods for monitoring their stability are discussed. Case studies from the literature are presented to examine how the choice of the working conditions and the analytical approaches is driven by the analytical and technical question to be answered, as well as the nature of the object from which the samples are collected.