The CIRAM recently dated two fossil woods: a "morta" oak and a bog yew. Both were found buried in the same location, in the marshes of Bessin and Cotentin, in Normandy (Calvados and Manche). And it must be said that the state of preservation of these two fragments is remarkable! Radiocarbon analyses place the oak between 4,344 and 4,066 BCE (Before Common Era), and the yew between 2,027 and 1,778 BCE. Despite their 6,000 and 4,000 years of age, these woods retain an almost intact structure and visual appearance.

But how to explain such preservation? And what do these ancient woods tell us about the history of landscapes? Here's a brief overview of a material as fascinating as it is precious.

Extraction of a morta tree by Atelier JHP.
(source: Le morta – JHP Workshop)

Morta : wood from submerged forests

Morta is a particularly ancient oak species found buried in the peat of marshes. Hidden there for millennia, it now constitutes as an exceptional material at the crossroads of geoarchaeology, wood science, and fine craftsmanship.

Furthermore, the archaeological surveys carried out during the dredging of the Brière canals, undertaken by the Syndicat du Bassin Versant du Brivet (SBVB), show that the peat deposits constitute genuine environmental archives. These millennia-old plant remains make it possible, in particular, to document:

• Variations in water levels in the marshes,
• The phases of burial of ancient forests,
• Traces of ancient human activity (charcoal, detrital deposits),
• Landscapes evolution since the Neolithic period.

The woods are thus integrated into a global reading of the territory, both archaeological and paleo-environmental. Radiocarbon analyses place the origin of the morta between the end of the Neolithic and the beginning of the Bronze Age. It therefore grew about 5,000 to 7,000 years ago, in a forest environment that has since disappeared.

And indeed, this period, marked by significant hydrological changes in the marshes, led to the gradual burial of the trees under peat deposits. This burial deprived the dead trunk of oxygen, preventing its usual decomposition.

The processing and marketing of morta

The commercial harvesting of bog oak is now strictly regulated: it takes place over a short period each year, in areas defined by local authorities. In the Brière marsh, for example, harvesting is only permitted for six weeks a year, from September 15th to October 30th, when the marsh is not too flooded, and the extraction site is located in conjunction with the Brière Regional Natural Park (PNRB). The ground is probed, and any wood found is harvested without mechanical assistance to preserve the integrity of the soil; the site is then filled in after extraction. An application for Protected Geographical Indication (PGI) status for the Brière marsh holly (morta) is currently under consideration to safeguard and regulate the harvesting of this unique natural heritage as much as possible.

Nowadays, this material is particularly prized for its technical and aesthetic properties. In the past, it was used to make sturdy frames or as firewood. Today, it is no longer sold in its raw state: it is transformed into knives, pens, pipes, sculptures, or other small turned or carved objects.

Silence, it’s growing! Video of the harvesting and processing of a morta by Atelier JHP.
(source: Le morta – JHP Workshop and Le morta – Silence, ça pousse ! – France Télévisions)

Analyses conducted by CIRAM

But let's get back to our samples: under these anoxic conditions, our two Calvados wood essences underwent a long fossilization process, making them resistant to decay in natural conditions. This anaerobic context is responsible for the exceptional preservation and the slow transformation into a dense, dark, and stabilized material. As we mentioned earlier, carbon 14 dating reveals two burial periods, even though we found our oak and yew in the same location. We can reasonably infer several phases of rising and falling water levels. These variations explain the decline of the trees and their subsequent progressive entrapment in peat deposits.

For oak essence, black is obviously not its original color, as it is a wood with originally brown and light hues. And it is this particular coloration, a testament to the chemical interactions that have occurred over millennia in humid environments, that gives it its aesthetic charm, particularly prized for art objects. Under the same conditions, yew wood (Taxus baccata) has darkened slightly, whereas it is usually rather orange-brown.

Wood species analyzed by CIRAM laboratories: "morta" oak (black) and swamp yew (brown).

Anatomical Analysis of Wood Species

Our oak sample was compared to a contemporary oak. The cross-section of this thousand-year-old oak reveals all the characteristic features of the deciduous oak genus, namely:

• A porous initial zone,
• Very wide wood rays, clearly visible to the naked eye, and others that are very thin,
• A tangential alignment of large vessels filled with tyloses in the earlywood and small vessels forming flame-like structures in the latewood.

The curvature of the growth rings is slight: the tree was therefore of large diameter and its growth was slow. Consequently, it was an old specimen. An observation that attests to the incredible preservation of the plant from its death to the present day!

Cross-section of a Morta sample (left) and a contemporary oak (right) after fine-grit sanding (x1200).

Technological Analysis of Wood Species

The analysis of our plants presents particular mechanical characteristics. Indeed, the mineralization of the wood during burial was accompanied by a significant modification of their densities. The average measured on several samples of our "morta" oak gives us an average value of 974 kg/m³. However, according to the Tropix technical sheet published by CIRAD, the density for a sessile oak or a pedunculate oak (Quercus petraea or Quercus robur) is around 740 kg/m³, which is an increase of 31% (source: Quercus robur / petraea technical sheet).

For its part, our if has undergone an equally spectacular mineralization: measurements taken on 6 samples give an average of around 750 kg/m³, whereas the usual density is between 480 and 600 kg/m³, representing a densification of 24 to 56%! This significant increase in density reflects the physico-chemical transformations of wood in a water-saturated, oxygen-poor environment, which permanently alter its mechanical properties.

A denser wood, but more difficult to work with

This high density makes them particularly resistant materials but also demanding to work with. Working with bog oak requires specific tools and expertise, as it is very dull (carbide-bladed tools, negative cutting angles, reduced passes to limit vibrations, slow and controlled work, etc.).

Interactive experience: find the bog oak!

What if you put theory into practice? As part of a Scientific Game Jam (March 10–12, 2023), an online video game was designed in just 48 hours around bog oak. The premise: explore a marsh, probe the ground… and try to locate buried logs, just like artisans do in the field.

This serious game offers a unique immersion in prospecting methods, translating scientific data into an interactive experience accessible to everyone. We bet you'll be digging! 😉

Screenshot from Planet Bog, a serious game dedicated to the search for morta.
(source: Planet Bog and Planet Bog Tutorial)

Acknowledgments and Sources

All of the data used in this article comes from geoarchaeological research conducted by the Loire-Atlantique Archaeology Department as part of the monitoring of the dredging of the Brière Marsh by the Brivet Watershed Authority, the Grande Brière collective geoarchaeological research program (team led by Yann Le Jeune, Loire-Atlantique Archaeology Service), various journalistic articles, as well as field observations and technological analyses of the material. We also thank Jean-Henri Pagnon, the creator of Morta knives, for his valuable advice and permission to use his photographic resources

• Le Jeune, Y. (2025), Geoarchaeology of the Grande Brière marsh – PCR project, UMR 6566 CReAAH, Loire-Atlantique archaeology service, 51 p.
• Le Jeune, Y. (2024), Pays de la Loire, Donges, Saint-André-des-Eaux, Saint-Joachim, Saint-Lyphard, Saint-Nazaire (44) – Brivet Watershed Study Followed by the Dredging of the Grand Marais de Brière – Phase 3, 2023, Archaeological Assessment Report, Nantes: Loire-Atlantique Archaeology Department, 308 p.
• Ouest-France (2024), The morta, oak from the Brière marshes, candidate for PGI
• The Echo (2025), Brière. The bog oak: 10 things to know about this wood buried for 5,000 years in the marshes of Brière
• Silence, it's growing! (2022), Video – The dead
• CIRAD Tropix, technical sheet Quercus robur / petraea.
• Scientific Game Jam (2023), Serious Game "Morta " – 48-hour development (March 10–12, 2023)
• Morta knives, photos, documentation, and video

Jennifer Coët

As the Communications & Digital Marketing Manager at CIRAM, Jennifer combines a background in science with a specialization in marketing, communications, and event management. She currently works to promote the expertise and projects of the CIRAM laboratory.

Choosing the right dating method in an archaeological context is an essential step. Depending on the nature of the material and the discovery context, scientists use different techniques. Carbon-14 dating, thermoluminescence (TL), and optically stimulated luminescence (OSL) each address specific issues.

Discover their principles, their fields of application, their limitations, and the criteria that allow choosing the most suitable method for each archaeological context.

Three dating techniques, three distinct scientific approaches

Carbon-14 dating

Carbon-14 dating (radiocarbon dating) is based on measuring the radioactive decay of the ¹⁴C isotope, naturally present in living organisms. Upon the organism's death, carbon exchange with the environment ceases, and the isotope begins to decay with a half-life of approximately 5,730 years. By measuring the residual amount of ¹⁴C relative to stable carbon ¹²C, the organism's date of death can be estimated.

It is used in archaeology as it offers an average precision of ±20 to 200 years. It allows dating:

Carbon-14 dating only applies to organic materials, thus excluding ceramics, stones, metals, or mineral sediments. It is also sensitive to modern contamination (bacteria, roots, infiltrations) which can falsify the results. It is therefore crucial to carefully carry out sample collection to ensure reliable scientific dating.

Thermoluminescence (TL)

Thermoluminescence dating is based on measuring the light emitted by a mineral when it is reheated in a laboratory. This technique thus analyzes electrons trapped in the crystalline structure of the material since its last exposure to high temperatures, generally during its manufacture or its use in a hearth. These electrons accumulate due to the natural radioactivity of the environment and retain a measurable "signal".

In the laboratory, controlled heating is carried out, releasing this signal in the form of luminescence. The more intense the signal, the longer the period that has elapsed since the last heating.

We will use thermoluminescence to date:

Thermoluminescence covers a chronological range between approximately 300 and 500,000 years, with an average accuracy of ±10%.

However, this technique has certain limitations:

• It is destructive: a significant fragment of the material is taken for analysis,
• It is sensitive to potential subsequent heating, whether natural or anthropogenic,
• It requires precise knowledge of the ambient radioactivity in which the material was buried to accurately calculate the dating.

As with any method based on accumulated signals, the quality of the sample and context data is crucial to ensuring the reliability of the results.

To learn more: Absolute dating by thermoluminescence: some archaeological questions.

Optically Stimulated Luminescence (OSL)

Optically stimulated luminescence (OSL) dating is based on measuring the light signal emitted by minerals, generally quartz or feldspar, when they are exposed to controlled light in a laboratory. This signal corresponds to the accumulation of trapped electrons in the mineral's crystal lattice since its last exposure to light.

In other words, OSL dating makes it possible to estimate when the sediment was buried, i.e., the last time it was exposed to daylight. It is a direct scientific dating method for sedimentary events. This technique is particularly useful in archaeological contexts where organic matter is absent.

The OSL will thus be used for dating:

OSL dating covers a time range from approximately 1,000 to 700,000 years, with an average accuracy of ±5 to ±15% depending on the context of the object.

However, it requires a very strict sampling protocol. Samples must be protected from light as soon as they are extracted, as even brief exposure to daylight can erase the signal. They are usually collected using opaque tubes that are sealed immediately under controlled conditions.

This method also requires specific equipment for sample preparation and analysis, as well as great rigor in data processing to account for the site's natural radioactivity. As with other luminescence dating techniques, the reliability of the scientific dating depends directly on the quality of the sample collection, sediment preservation, and control of environmental parameters.

Which archaeological dating method should you choose: Carbon-14, TL, or OSL?

Comparison table of methods

The table below summarizes the main differences between these three methods to facilitate their comparison.

Which criterion for which context?

The choice of the most appropriate method depends on several factors:

• Nature of the material: a fragment of wood → C14, pottery → TL, sediment under occupation soil → OSL
  
• Conservation: if organic matter is absent or too degraded, TL or OSL become the only options.
  
• Research question: dating an event (e.g., burial of a level, last use of a hearth)
  
• Stratigraphic context: choice of a non-destructive or complementary method

However, the study context within excavations can include various elements to analyze. Combining these methods often leads to a more robust chronology. A specialized laboratory can thus recommend the most relevant analyses based on available materials and study objectives.

Example: on a Neolithic site with a hearth, pottery, and sedimentary layer:

• Charcoal → carbon-14 dating
  
• Terracotta → thermoluminescence dating
  
• Sediments → OSL dating

In conclusion, choosing between radiocarbon dating, thermoluminescence (TL), and optically stimulated luminescence (OSL) depends primarily on the material studied, the archaeological context, and the scientific question asked. These methods are not mutually exclusive: they are complementary and can be combined to refine the chronology of a site or an object.

In case of doubt, CIRAM experts will guide you in choosing the most suitable analyses and in interpreting the results to establish a reliable chronology consistent with your archaeological context.

Patrick Rossetti

Patrick is the director of the Archaeology Department at the CIRAM laboratory. He coordinates projects involving dating, isotopic analysis, and the characterization of archaeological materials, in collaboration with research institutions, museums, and archaeologists in France and abroad (ORCID: 0000-0001-8770-6732).

Mass spectrometry is a major analytical technique in archaeology. It can be used to date remains using carbon 14 as well as to study the composition of materials, identify organic residues, or analyze stable isotopes to better understand ancient societies. Its precision and sensitivity allow information to be obtained from minute quantities of matter.

Organic residues found in amphorae, pottery, or flasks also provide information about ancient practices. Their analysis can reveal oils, fats, resins, or other substances. Depending on their nature, researchers use different methods, such as infrared spectroscopy, Raman spectroscopy, or chromatography coupled with mass spectrometry.

These techniques address specific objectives and can complement each other. This article presents their principles, their main applications in archaeology, and the information they allow us to obtain.

Understanding mass spectrometry in archaeology: principles and techniques

Mass spectrometry is based on the analysis of atoms or molecules present in a sample. Depending on the technique used, it can be used to date remains, study their chemical composition, or analyze their isotopic signatures in order to obtain information about their origin, use, or history.

The principle of mass spectrometry applied to the analysis of archaeological materials

The principle of mass spectrometry consists of ionizing a sample, then separating the ions according to their mass. Scientists can thus identify the chemical elements, isotopes, or molecules present, even when the quantities analyzed are extremely small.

This sensitivity allows for the study of precious or very small archaeological remains while obtaining particularly precise results. Depending on the study's objectives, researchers use different mass spectrometry techniques, each addressing a specific issue.

The main mass spectrometry techniques: AMS, IRMS and spectrometry coupled with chromatography

Several methods are used in archaeology:

Each technique addresses a specific scientific problem. They are often complementary and can be combined within the same research project.

Concrete applications: what mass spectrometry reveals in archaeology

Beyond the performance of the instruments, the interest of mass spectrometry lies in the information it provides on archaeological remains. Depending on the technique used, it can date an object, reconstruct the lifestyles of ancient populations, or identify the substances present on an artifact.

Date the archaeological remains

Accelerator Mass Spectrometry, or AMS, remains the reference method for radiocarbon dating in archaeology today. Unlike conventional techniques, it allows for the dating of samples weighing a few milligrams with extreme precision by directly measuring the 14C/12C ratio. It is thus the preferred method for analyzing delicate objects or those of great heritage value (human bones, funerary textiles, charcoal in sealed contexts). It provides precise archaeological dating, limiting biases related to contaminants or sample size.

Reconstitute the lifestyles of ancient populations

IRMS stable isotope analysis, in turn, opens up another field of interpretation in an archaeological context. Thanks to the study of stable isotopes of carbon, nitrogen, oxygen, or sulfur, it becomes possible to trace diets, identify areas of origin, or even distinguish social practices (for example: identifying differentiated diets according to status or gender).

Identify the organic residues preserved on the objects

Chromatography coupled with mass spectrometry (GC-MS or LC-MS) can be used to explore organic molecules trapped in artifacts: food lipids, resin or wine residues, degraded proteins, etc. These analyses provide functional information on the use of artifacts (containers, tools, ornaments) and are invaluable for paleoenvironmental studies or proteomic approaches.

Complementary techniques for analyzing organic residues

Infrared spectroscopy (IRTF) allows for the characterization of major organic compound families, such as oils, fats, or resins. Raman spectroscopy also provides information on material composition and can complement chromatographic analyses. The choice of methods depends on the nature of the residues, their state of preservation, and the archaeological questions being studied.

Limits, precautions and interpretation of results in an archaeological context

While the possibilities offered by mass spectrometry for archaeology are vast, they nevertheless require the implementation of rigorous study protocols. Sampling must therefore be anticipated upstream of the excavation in order to understand: the nature of the material, the conservation conditions, and any risks of contamination. Reliable interpretation indeed relies on close collaboration between field teams and the specialized analytical laboratory for archaeological study.

Finally, the results cannot be read in isolation from the research context: dating, isotope analysis or organic identification, these techniques do not deliver absolute truths, but their results offer powerful indicators when cross-referenced with archaeological data.

In conclusion, mass spectrometry is now an essential tool for the study of archaeological remains. Thanks to its various techniques (AMS, IRMS, GC-MS, or LC-MS), it allows for the dating of materials, the identification of their composition, and the provision of new information about ancient societies. Combined with field observations, these analyses contribute to building a more complete scientific interpretation of sites. The CIRAM laboratory thus supports archaeology stakeholders by implementing these different analytical approaches, adapted to the challenges of preventive, programmed, and research archaeology.

Olivier Bobin

Olivier holds a master’s degree in chemistry (1996) and a Ph.D. in Archaeomaterials Physics (2001) from the University of Bordeaux. In 2005, he co-founded the CIRAM laboratory with Richard Chéret, and today serves as its co-director and scientific director.

Archaeologists must establish reliable chronologies to understand the occupation, evolution, and uses of the sites studied. This step is a fundamental element of their scientific approach. However, due to the diversity of contexts, materials, and research objectives, no single method can guarantee irrefutable dating on its own.

It is for this reason that researchers today adopt the crossing of several dating methods as a reference approach in archaeological contexts. The combination of several techniques such as radiocarbon dating, thermoluminescence, OSL, dendrochronology, and ESR allows them to refine, validate, and secure the results of their studies. To achieve this, however, they must have a good understanding of the strengths and limitations of each method, respect the protocols, and understand the decisive role of specialized laboratories.

In this article, we offer a review of dating techniques in an archaeological context, an examination of their complementarity, and the importance of collaborating with an expert laboratory.

Understanding the diversity of dating methods in archaeology

In an archaeological context, knowledge of the specifics of dating and materials analysis methods is essential for optimizing analytical strategy right from the outset of a project. This enables research teams to limit the impact of field, material and schedule constraints specific to this environment.

Dating methods for archaeology: an overview of absolute and relative techniques

The dating process in archaeology is based on two main methodological groups: absolute dating and relative dating. Each group serves distinct purposes, depending on the nature of the artifacts, the excavation context, or the constraints of expected chronological precision.

Absolute methods, such as carbon-14 dating, thermoluminescence, dendrochronology, OSL, ESR, or U-Th, allow an age to be assigned in years. They are applicable to various materials such as organic matter (charcoal, bones), ceramics, sediments, building materials, etc.

On the other hand, relative dating techniques, such as archaeological stratigraphy, typology or seriation, enable us to chronologically order layers and objects without providing an absolute age. They are essential for contextualizing finds on site, particularly in complex or disturbed environments.

To do this, archaeologists need to choose which method to use, depending on the type of archaeological material to be dated (wood, ancient pottery, ceramics, bone, sediment), its conservation, its context and the chronological resolution required. It is therefore important, right from this stage, to consult with an analytical laboratory in order to avoid possible biases and anticipate analytical constraints.

Advantages, limitations and technical challenges of the various methods

Each technique has a defined field of application, specific error margins, and strict protocols. It is precisely this complementarity that justifies their joint use.

For example, carbon-14 dating is a reliable technique for organic materials up to 50,000 years old, but it remains sensitive to recent contamination. Thermoluminescence and OSL, on the other hand, are reserved for materials that have undergone a final heating or exposure to light (ceramics, sediments), with uncertainties related to the annual dose received.

Other useful methods, such as ESR or U-Th, are adapted to specific contexts (enamels, limestones, fossil teeth). Dendrochronology can achieve annual precision when a suitable reference is available, but its application remains limited to species and regions with reference chronologies.

The reliability of dating for archaeology therefore depends less on a single method than on a reasoned choice, informed by the limitations of each chosen technique and the imperatives of the field.

Cross-fertilizing methods to make archaeological chronology more reliable

No method, however effective, is sufficient on its own to establish a reliable chronology of the analyzed sample. Cross-referencing dating methods therefore allows for the construction of more robust and better-documented chronologies.

Why adopt a multi-technique approach to archaeological dating?

Cross-referencing several dating methods in archaeology enables us to compare, refine or confirm the results obtained. By combining different techniques based on different physical or chemical principles, we reduce the margins of error associated with each method, while increasing reliability.

Let's take the example of a prehistoric site combining hearths, ceramic furniture and bone remains. Radiocarbon dating on charcoal can be combined with thermoluminescence dating on the heated ceramic fragments, or OSL dating on the surrounding sediments, to obtain a more precise view of the sample's history. This chronological triangulation makes it possible to exclude anomalies (e.g. recent carbon-14 pollution) or to specify the actual age of deposition.

Another common case for archaeologists is the dating of bones, which is regularly subject to post-depositional leaching or contamination. Using ESR dating in parallel, which is more stable over time, helps to secure the historical interpretation. This type of approach (combination) is particularly recommended in complex contexts (caves, disturbed layers, tropical environments), or when the dating of artifacts & archaeological samples needs to be integrated into long sequences.

Towards a coherent chronology: interpreting, modelling and exploiting results

As we've seen, combining analysis methods limits their limitations and adds their own advantages. However, crossing techniques is not enough: the results must be integrated into a coherent chronological framework. This phase relies on advanced statistical tools, notably Bayesian models. These enable data to be linked together, while taking into account the uncertainties inherent in each measurement.

Dating for multi-technique archaeology makes it possible to reconstruct phases of occupation, to better define the dynamics of a site, or to redefine technical periods. This advanced methodology is a decisive asset for dating prehistoric sites, built structures and burial contexts.

Finally, this approach further enhances the scientific value of the results, their credibility with heritage institutions, and their potential for dissemination in specialized publications. In short, the cross-fertilization of techniques is not a simple choice, but becomes a strategic lever for any dating approach in demanding archaeology.

The role of a specialized laboratory in a multi-technique strategy

The choice of a multi-technique strategy therefore relies on a precise analysis of the archaeological context, available materials, and the scientific objectives of the project. A specialized laboratory intervenes from the initial stages to guide sampling and define the most suitable analytical protocols.

This expertise makes it possible to limit biases related to contamination, material preservation, or the inherent limitations of each method, in order to construct coherent and scientifically usable chronologies.

Thanks to its expertise in radiocarbon dating and archaeological material analysis, CIRAM supports professionals in implementing analytical strategies tailored to their specific challenges.

Patrick Rossetti

Patrick is the director of the Archaeology Department at the CIRAM laboratory. He coordinates projects involving dating, isotopic analysis, and the characterization of archaeological materials, in collaboration with research institutions, museums, and archaeologists in France and abroad (ORCID: 0000-0001-8770-6732).

The dating of mummies is an essential analysis that enables archaeologists to accurately reconstruct the history of ancient civilizations. Among the various methods of archaeological dating,carbon-14 analysis is an essential tool for researchers. However, its application to mummies often raises methodological challenges such as sample selection, contamination risks, chronological limits and the corrections needed to avoid them.

In this article, we explore in detail the process of radiocarbon dating: its specific applications to Egyptian and Andean mummies, as well as the scientific solutions available to us that optimize the precision of carbon-14 dating of mummies.

Specific features of carbon-14 dating of mummies

Carbon-14 dating is an essential analytical method for helping archaeologists establish the chronology of mummies. However, archaeologists need to guarantee reliable results, and a number of technical and methodological issues arise. These include sample selection, contamination and isotopic bias.

Type of samples to be analyzed

To date a mummy using carbon-14, researchers must collect organic materials present. The main samples available to them are:

• Mummified biological tissues: skin, hair, tendons, or bones.
• Mummy bandages: often made of linen, an organic material directly usable for analysis.
• Biological residues: dried fluids, pigments applied to the body, or embalming resins. Their use can, however, pose problems for dating, as we will see later.

Mummy hair is a particularly interesting material for carbon-14 dating due to its resistance to degradation. A study has shown that a specific protocol allows for the extraction of keratin from the hair cortex and requires only about twenty milligrams of sample, which minimizes the impact on the mummy's integrity while providing accurate dates. This technique is particularly well-suited for mummies preserved in museums.

Why are mummies more difficult to date?

Although the analyzable samples on a mummy are varied, several factors complicate carbon-14 dating:

• Modern contamination: exposure to recent varnishes, resins, or bitumen can distort the measurement of the ¹⁴C/¹²C ratio.
• Conservation environment: the development of micro-organisms could artificially rejuvenate dating, if they are not strictly eliminated.
• Organic matter aging: poor preservation could prevent enough matter from being collected for precise dating.

A study conducted on the golden mummy of Dunkirk demonstrated that sample selection and chemical pretreatment were crucial to ensure the reliability of the results. The selective extraction process of keratin from hair thus made it possible to eliminate exogenous materials and obtain reliable dating.

How is the dating of a mummy carried out?

The reliability of a dating of a mummy using carbon 14 relies on a rigorous protocol for sampling, preparation, and laboratory analysis. Each step aims to eliminate possible biases and ensure optimal accuracy despite the challenges inherent in ancient materials.

Sample preparation and extraction

Carbon-14 dating requires meticulous sample preparation. This involves several crucial steps:

• Mechanical and chemical cleaning: this refers to chemical pre-treatment techniques (ABA method: acid-base-acid) for removing modern contaminants.
• Selection of the most reliable fractions: mummified hair is preferred as it offers better resistance to environmental alterations.
• Isotopic filtering: the analysis of carbon isotopic ratios makes it possible to detect potential anomalies.

Laboratory analysis

C14 analysis relies on precise laboratory steps to guarantee reliable and scientifically robust results:

• Measurement of the ¹⁴C/¹²C ratio: accelerator mass spectrometry (AMS) allows the analysis of very small samples.
• Isotopic bias control: are adjustments to account for natural isotopic fractionation.
• Calibration of results: is based on the IntCal 20 or SH Cal20 calibration curves, essential for correcting historical fluctuations in carbon 14.

Examples of mummy dating

Egyptian mummies: dating burial bandages

The linen bandages that wrap Egyptian mummies offer excellent reliability for carbon-14 dating. A study carried out on New Kingdom mummies confirmed their belonging to the 18th Dynasty thanks to accelerator mass spectrometry (AMS). This technique indeed allows for the analysis of very small samples, thus minimizing the impact on the mummy's integrity.

The study of funerary textiles, carried out notably at El Deir in Egypt, has opened new perspectives for the dating of mummies. Researchers were thus able to identify different types of textiles, including new linen bandages and fabrics from daily life. This approach, using a reference material, not only allows for the dating of mummies but also provides information on funerary practices and the social status of the deceased.

A remarkable example is that of the mummy of Nesi-Khons, dated between the 4th and 1st centuries BCE. The bandages of this mummy contained not only an Etruscan text on linen but also a papyrus from the Egyptian Book of the Dead, thus offering a unique opportunity to cross-reference textual data and carbon-14 dating.

Andean mummies: environmental challenges

A recent study on mummies discovered in the Argentine Andes used an innovative approach: researchers performed a cross-dating by dating the louse nits found in the mummies' hair. This method allowed them to estimate the age of these mummies between 1300 and 2300 years, while also providing valuable genetic information about the mummified individuals.

Complex cases: contaminated mummies

Some mummies were treated in the 19th century with modern substances. To counteract these contaminations and achieve reliable dating, scientists must thoroughly clean the samples before analysis to obtain usable results. The case of the mummy of Ramesses II perfectly illustrates this contamination problem.

Natural mummies: challenges and opportunities

Natural mummies, bodies formed under specific environmental conditions that ensure their preservation, present unique challenges for dating.

For example, bodies preserved in permafrost or peat may have absorbed ancient carbon, skewing the results of carbon-14 dating. In such cases, scientists combine several methods beyond C14 dating, such as pollen or wood analysis, to obtain reliable dates.

Carbon-14 is currently the reference method for dating mummies. Thanks to rigorous preparation protocols and accelerator mass spectrometry (AMS), it is possible to obtain precise dates on various organic materials while limiting the risks of contamination. Combined with data from excavations, these results provide a better understanding of funerary practices, preservation conditions, and the history of ancient civilizations. The CIRAM laboratory implements these methods to support research projects and archaeological studies on ancient human remains.

Patrick Rossetti

Patrick is the director of the Archaeology Department at the CIRAM laboratory. He coordinates projects involving dating, isotopic analysis, and the characterization of archaeological materials, in collaboration with research institutions, museums, and archaeologists in France and abroad (ORCID: 0000-0001-8770-6732).

Preventive archaeology makes it possible to study archaeological remains that are likely to be threatened by development projects. To understand the history of sites and place discoveries in their chronology, archaeologists can rely on carbon-14 dating.

This method allows for the estimation of the age of organic materials from remains, such as charcoal, bones, or plant remains. Its relevance, however, depends on the choice of samples and their relationship with the archaeological structures studied.

Preventive archaeology: definition and challenges

In France, preventive archaeology is governed by the law of January 17, 2001. It aims to safeguard, through scientific study, elements of archaeological heritage threatened by public or private works.

It generally takes place before the implementation of the improvements and includes two main stages:

• The archaeological diagnosis: soundings make it possible to assess the presence, nature, and state of preservation of the remains.
• The archaeological excavation: when the diagnosis reveals remains requiring in-depth study, an excavation allows for their documentation before the work begins.

These operations produce a great deal of information about past human occupations. Carbon-14 dating can complement field observations by providing chronological benchmarks, especially when discovered remains contain organic materials suitable for analysis.

Why use carbon 14 in preventive archaeology?

Carbon-14 dating helps archaeologists determine when organic material stopped exchanging carbon with its environment. It can thus help date certain occupations, structures, or human activities uncovered during diagnostics and excavations. Its use depends on the remains discovered and the scientific questions asked. It can notably contribute to:

• Dating combustion structures, from charcoal associated with a hearth or archaeological feature.
• Studying human occupations, through plant remains, bones, or other organic materials linked to an archaeological level.
• Specify the chronology of a site, by comparing several datings from distinct contexts.
• Verify chronological hypotheses, by confronting the results with stratigraphic observations and other archaeological data.

Carbon-14 dating, however, does not allow for the direct dating of all remains. It applies to materials containing carbon of biological origin and does not necessarily provide the exact age of a structure or event. The relevance of the result depends on the link between the analyzed material and the element being dated.

To understand the scientific principle of this method, its applications, and its limitations, also consult our article: How does carbon-14 dating work?.

How to choose samples for dating?

The choice of sample is a crucial step in preventive archaeology. A sample must be suitable for the dating method, sufficiently well-preserved, and relevant to answer the archaeological question. Several types of materials can be studied:

The context of discovery is as important as the nature of the material. The stratigraphic position, the relationships between the remains, and any possible soil disturbances must be documented to allow for relevant interpretation.

Charcoal discovered in a structure may, for example, be older than it if the wood came from a long-dead tree or had been reused. Similarly, a material displaced after its deposition may not directly date the level in which it is found.

It is therefore essential to select samples whose link to the event studied is as direct as possible.

How to interpret the results in their archaeological context?

Carbon-14 dating provides an estimate of the age of the analyzed material. To draw conclusions about the history of a site, archaeologists must compare it with other information gathered during fieldwork.

Cross-reference datings and stratigraphic observations

Stratigraphy allows for the study of the succession of archaeological layers and structures. It helps to understand the chronological relationships between the different elements discovered.

Carbon-14 dating can complement this reading. Several samples from well-documented contexts can, in particular, help to refine the chronology of an occupation or to verify if remains are contemporary.

Results that seem contradictory do not necessarily mean that one of the dates is wrong. They may reveal the presence of residual materials, displacement of remains, or distinct occupation phases. Their interpretation therefore requires returning to the context of each sample.

Take into account the limits of the method

The reliability of a dating depends notably on the state of conservation of the material, the risks of contamination, and the quality of its preparation and analysis.

Calibration is also essential for converting radiocarbon age into calendar date intervals. The results must be interpreted taking these intervals into account, and not as a systematically determined exact year.

Finally, radiocarbon dating does not answer all chronological questions. Other methods may be more suitable for certain materials, notably thermoluminescence for mineral materials that have been heated or optically stimulated luminescence for certain sediments. The choice depends on the nature of the artifact and the event one wishes to date.

To delve deeper into the subject, also consult our article: Carbon 14, thermoluminescence TL and OSL: which dating method to choose?

Patrick Rossetti

Patrick is the director of the Archaeology Department at the CIRAM laboratory. He coordinates projects involving dating, isotopic analysis, and the characterization of archaeological materials, in collaboration with research institutions, museums, and archaeologists in France and abroad (ORCID: 0000-0001-8770-6732).

Pottery, amphorae, and ancient vessels can retain traces of the substances they once contained. By coupling different analytical techniques, such as infrared spectrometry, Raman spectrometry, and chromatography, scientists can detect and identify some of these organic residues.

The analyses performed by CIRAM allow for the characterization of oils, fats, resins, or even residues of fermented beverages. This information contributes to a better understanding of the dietary habits, artisanal practices, and trade exchanges of ancient peoples.

Organic residues: understanding old habits and practices

The organic residues found in dishes, vases, amphorae, or flasks constitute valuable clues about the practices of ancient populations. They can provide information on dietary habits, methods of food preparation and preservation, as well as trade and certain artisanal or funerary activities.

Analyzing these residues allows for the identification of various substances, such as oils, fats, or resins. Their interpretation must, however, take into account their state of preservation and the archaeological context, as transformations occurring over time can complicate the identification of their initial nature.

Reconstruct dietary habits and products used

Traces of fats and oils can provide clues about the foods prepared, stored, or transported in ancient vessels. Other substances, such as resins, can attest to artisanal uses or specific practices.

This information contributes to a better understanding of the function of the objects and the activities with which they were associated. It complements the study of the shape of the vessels, their provenance, and the other remains discovered at the archaeological site.

Organic residue analysis methods

The residues found in ancient pottery often consist of complex mixtures. To identify the substances present, CIRAM scientists can combine several analytical techniques, depending on the nature of the sample and the information sought.

What are the limitations of organic residue analysis?

The identification of organic residues depends on several factors, notably the quantity of material available, the state of preservation of the molecules, and potential contamination from the soil or the container itself. Some substances degrade over time, while others may present similar chemical signatures. Identifying a family of compounds therefore does not always make it possible to determine with certainty the initial product or its exact use.

This is why analytical results must be compared with the archaeological context and other information available on the object. This approach makes it possible to formulate better-supported hypotheses about the substances present and the practices with which they may be associated.

CIRAM's expertise in 【1】archaeometric analysis【/1】

CIRAM supports archaeology stakeholders in the scientific study of materials and remains. The analysis of organic residues allows for the search for clues about substances present in ancient containers and contributes to the understanding of the practices of ancient societies. The choice of techniques depends on the nature of the sample, its state of preservation, and the archaeological research question. The interpretation of the results then makes it possible to place the information obtained back into its context and to discuss the possible hypotheses.

To learn more, visit our page dedicated to organic residue analysis in archaeology.

Patrick Rossetti

Patrick is the director of the Archaeology Department at the CIRAM laboratory. He coordinates projects involving dating, isotopic analysis, and the characterization of archaeological materials, in collaboration with research institutions, museums, and archaeologists in France and abroad (ORCID: 0000-0001-8770-6732).

Charcoal discovered during archaeological excavations is not only used for carbon-14 dating. Their study also makes it possible to identify wood species, reconstruct ancient environments, and better understand the practices of past societies.

This discipline, called anthracology, is based on the observation of the anatomical structures of charred wood. Discover how archaeological charcoal is analyzed in the laboratory and what information it provides to archaeologists.

What is anthracology and its role in archaeology?

Anthracology is a branch of archaeobotany specializing in the study of charcoal from archaeological contexts. It relies on microscopic observation of the anatomical structures of charred wood to identify plant families, genera, and, when possible, species.

The charcoal found during preventive excavations can originate from hearths, combustion structures, burnt building elements, or natural fires. Depending on their state of preservation and combustion conditions, charcoal can retain enough anatomical structures to allow for botanical identification.

However, analysis is not limited to simple recognition: it reveals human practices (choice of species, harvesting methods, combustion techniques) and the environments exploited by ancient societies.

Why is charcoal considered a precious remnant?

In the context of preventive excavations, charcoal holds a special place. It is both a witness to local paleovegetation and a material that can be used for carbon-14 dating (up to approximately 60,000 years).

In practical terms, anthracology helps archaeologists answer several strategic questions:

• What environments surrounded the excavated site? Charcoal helps to restore ancient vegetation and exploited woody resources.
  
• Which coals to choose for dating? Their nature, state of preservation, and archaeological context help in choosing relevant samples.
  
• How to avoid bias? Identifying the wood and the part of the tree used can help spot risks related to the "old wood" effect.

Anthracology alone does not allow for the reconstruction of an entire ancient landscape. It usefully complements other archaeobotanical approaches, such as palynology, which studies pollen, or carpology, which focuses on seeds and fruits.

In preventive archaeology, it thus contributes to better characterizing ancient environments, understanding the exploitation of plant resources, and guiding the selection of samples for carbon-14 dating.

How does an anthracological analysis take place in a laboratory?

Anthracological analysis begins with the preparation of charcoal surfaces, refreshed with a razor blade to make the anatomical structures more legible.

The samples are then observed according to the three anatomical planes of the wood: transverse, tangential longitudinal, and radial longitudinal. Examination of these different faces generally allows for the identification of the botanical family or genus, and sometimes the species.

Observations are made using a stereomicroscope (Olympus® SZ61 binocular loupe) and a dark-field metallographic microscope (Olympus® BX53M), under "natural" light (calibrated white light), coupled with digital cameras.

What anthracological criteria are analyzed?

Botanical identification is only one part of anthracological study. Specialists also examine several anatomical characteristics and alterations that provide information about the part of the tree used, the state of the wood before combustion, and the conditions under which it burned.

Identify the origin and the part of the tree used

• The presence of bark and pith: by simultaneously observing these two elements on a sample, we deduce the calibration of the stem.

• Reaction wood (characteristic of small branches or leaning trunks). This criterion, combined with a strong curvature, indicates that we are dealing with a small branch.

• Calibration assessment: analyzing the curvature of growth rings and the angle of woody rays will identify the part of the tree from which the charcoal originated. Charcoal is classified into 4 categories:

To determine the state of the wood before burning it.

• The presence of tyloses: tyloses form in the vessels of certain hardwoods during heartwood formation. The presence of tyloses helps us to determine potential species, but also to indicate the location of the sample.

• The presence of fungal hyphae: filaments can be observed in the vessels of charcoal. They indicate the development of fungi in the wood before its combustion, particularly during the degradation phases of a dead or dying tree. Their observation thus provides information on the state of the wood before its use.

• Degradation by boring insects or worms: similarly, the presence of galleries in coals is proof of an attack by boring insects or worms. It is possible to find the carbonized organisms in these galleries. These clues are proof that the wood was dead and rotten before its combustion. In some cases, the sapwood of a living subject can be attacked by such organisms.

Analyze the combustion conditions

• The presence of radial shrinkage cracks and vitrification: water-saturated wood will exhibit a large number of shrinkage cracks. Vitrification is a complex phenomenon that occurs during combustion. The aspects of vitrification depend on the nature of the wood (species, size, moisture content) and the combustion conditions (temperature and oxygenation of the firebox). We will distinguish 4 aspects of vitrification corresponding to 4 levels of carbonization:

Study of wood growth and its use

• The width of the growth rings and growth rate. A narrow width indicates that the wood grew slowly (unfavorable growth conditions or an old subject). Conversely, wider rings indicate greater growth, linked for example to favorable environmental conditions or a younger tree. Therefore, the growth rate, i.e. the regularity of the ring widths, indicates whether the subject grew uniformly or if there were events that temporarily hindered growth (climatic conditions, fungal attack, tree injuries, etc.).

• Woodworking traces: surface grooves or scratches can attest to work done on the wood using tools.

Archaeobotany and radiocarbon dating: why combine these methods?

Charcoal can be used to date an archaeological event through the measurement of carbon 14. However, the age of the wood analyzed does not always correspond to that of the event studied.

This is particularly the case with the "old wood" effect: charcoal from the heart of an ancient tree can be significantly older than the archaeological structure to which it is associated. Dating may then provide an age prior to the event being investigated.

Anthracological study helps to characterize fragments and select the most relevant samples, taking into account their nature and context. It does not eliminate all risks of error, but contributes to a better interpretation of the results.

Combining anthracology and radiocarbon dating thus allows for the cross-referencing of botanical and chronological information, in order to place the remains within their archaeological context.

Why are these observations important?

The observations made on the coals are compiled in tables and graphs, then presented in an analysis report.

Anthracological study thus makes it possible to better understand the plant resources exploited, the characteristics of the wood used, and certain combustion conditions. By cross-referencing this information with the archaeological context and, where relevant, with carbon-14 dating, specialists have complementary data for interpreting the remains.

Joey Montagut

Archaeobotanist, Joey graduated from the École Supérieure du Bois (Nantes – 2002). He specialized in the identification of archaeological and contemporary woods (Xylology) and charcoals (Anthracology).

The analysis of stable carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) present in bone collagen allows for the study of the diet of ancient populations. These methods provide information on the resources consumed by individuals, their terrestrial or marine origin, and their relative position in the food web (food chain).

Isotopic analysis thus makes it possible to better understand the dietary habits of a group, but also to highlight potential differences related to social and economic practices. From the results obtained on several individuals, scientists can characterize the major dietary trends of a population and contribute to answering archaeological questions.

How to determine diet using stable isotopes of carbon and nitrogen?

Carbon-14 dating is not the only technique used in archaeometry. The analysis of stable carbon and nitrogen isotopes also provides valuable information about the lifestyle of ancient populations.

The carbon isotopic ratio (δ¹³C) notably allows for the distinction of different food sources. Plants primarily use two types of photosynthesis, known as C3 and C4, which exhibit different carbon isotopic signatures.

• C3 plants, such as wheat, rice, or trees, generally show more negative δ¹³C values.
• C4 plants, such as corn and sugarcane, generally show less negative δ¹³C values.

These differences are found in the food chain and help characterize the resources consumed by humans and animals. The nitrogen isotopic ratio (δ¹⁵N) provides complementary information. In particular, it allows us to study the relative position of individuals in the food web and to better understand the contribution of different protein sources to their diet.

By combining carbon and nitrogen analyses, it is thus possible to study the major dietary trends of an individual or a group, notably the relative contribution of terrestrial and marine resources.

Why check the preservation state of bone collagen?

The interpretation of isotopic results depends on the quality of the analyzed samples. Over time, bone collagen can degrade or be altered by its environment, which risks compromising the reliability of the measurements.

The quantification of carbon and nitrogen concentrations, as well as the analysis of the C/N ratio, allow for the evaluation of the quality of the extracted collagen. A C/N ratio between 2.9 and 3.6 is generally considered compatible with well-preserved collagen for isotopic analyses and radiocarbon dating.

These criteria must, however, be interpreted in conjunction with other conservation indicators and according to the nature of the sample. They help determine whether the collagen is sufficiently preserved to allow for reliable exploitation of the results.

What do the results of the isotopic analysis teach us?

Stable isotope analyses of carbon and nitrogen provide information on the dietary habits of ancient populations, notably:

The interpretation of the results depends on the archaeological context, the environment, and the resources available at the time studied. Isotopic signatures do not always make it possible to identify a precise food, but they help researchers test hypotheses and better understand ancient lifestyles.

Studying a sufficiently representative set of individuals is essential for characterizing the dietary trends of a population and avoiding the drawing of general conclusions from a few isolated results.

What equipment is used for stable isotope analysis at CIRAM?

The analysis of stable carbon and nitrogen isotopes relies on two complementary pieces of equipment: an elemental analyzer and an isotope ratio mass spectrometer (IRMS).

The elemental analyzer allows for the measurement of carbon and nitrogen concentrations in the sample after combustion. The resulting gases are then introduced into the IRMS, which measures the isotopic ratios of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N). The results are expressed in per mille (‰), according to the δ notation used in isotopic geochemistry.

At CIRAM, these analyses are based on a vario ISOTOPE select elemental analyzer and an isoprime precisION isotope ratio mass spectrometer, from the brand ELEMENTAR. These instruments make it possible to characterize samples and produce the data necessary for the study of ancient diets.

CIRAM's expertise in isotopic analysis

Since 2005, CIRAM has supported archaeological studies with its expertise in dating and scientific analysis. Our teams interpret the results, taking into account the characteristics of the samples and research issues, and provide documented reports to help researchers utilize their data.

Patrick Rossetti

Patrick is the director of the Archaeology Department at the CIRAM laboratory. He coordinates projects involving dating, isotopic analysis, and the characterization of archaeological materials, in collaboration with research institutions, museums, and archaeologists in France and abroad (ORCID: 0000-0001-8770-6732).

Carbon-14 dating makes it possible to determine the age of organic matter and to trace the chronology of its formation. Applied to peat and organic sediments, it helps to reconstruct the evolution of natural environments, landscapes, and ancient ecosystems.

Thanks to its laboratory specialized in accelerator mass spectrometry (AMS) dating, CIRAM performs carbon 14 analyses on various organic materials, including wood, bones, charcoals, peats, and organic sediments.

Why date peat with carbon 14?

Peatlands formed over sometimes very long periods, dating back more than 10,000 years in some regions. They preserve valuable information on the evolution of environmental and climatic conditions, as well as on the interactions between human societies and their environment.

Carbon-14 dating makes it possible, among other things, to determine when peat formation began or to which period a studied layer of organic sediment relates. It thus provides useful chronological markers for the reconstruction of ancient environments. Combined with geomorphological, paleoecological, or archaeological data, the dates obtained help to trace the evolution of landscapes and human occupations.

However, the reliability of dating depends on several factors: the nature of the material analyzed, its state of preservation, the selection of the organic fraction, and its preparation before analysis. The choice of sample must therefore be adapted to the research question.

What types of peat and organic sediments can be dated?

Different types of peat and organic sediments can be dated using carbon 14. Their composition and degree of decomposition influence the choice of sample to be analyzed.

Fibrous peats

Fibrous peats contain more or less decomposed plant remains. These organic materials constitute potential substrates for radiocarbon dating and can provide information on peatland formation and environmental evolution.

Muddy peat

Muddy peats generally present organic matter that is finer and less easily identifiable than the plant remains found in fibrous peats. Their dating helps establish a chronology of organic deposit formation.

Silty peats

Silty peats also constitute samples that can be studied by carbon-14 dating. As with other types of peat, the nature of the organic matter and the sampling context must be taken into account to interpret the results.

How to prepare peat samples for carbon-14 dating?

The preparation of peat samples before carbon-14 dating depends on their composition and the organic fraction to be analyzed. It aims to eliminate contaminants that could interfere with the measurement and to isolate the material suitable for dating.

The main preparation steps vary depending on the type of peat:

For certain humic sediments, preparation may also require separating the soluble and insoluble fractions. Sieving, filtration, centrifugation, or precipitation steps can then be implemented according to the protocol applied.

The choice of preparation is essential to limit the risks of contamination and obtain a usable result. It depends on the nature of the sample, its state of preservation, and the scientific question.

How to interpret the results of a carbon-14 dating?

From radiocarbon age to calibrated date

The measurement of carbon 14 provides a conventional radiocarbon age, generally expressed in years BP (Before Present), with "present" conventionally set to the year 1950. This age does not directly correspond to a calendar date. To obtain an estimate of the age in calendar years, a suitable calibration curve must be used. This conversion takes into account variations in the concentration of carbon 14 in the environment over time.

The result is therefore generally expressed in the form of one or more calibrated date ranges, accompanied by their probability level.

Given the phrasing, "Place the date in its scientific context" seems the most natural and direct translation.

A radiocarbon date must be interpreted taking into account the nature of the sample, the fraction analyzed, and the sampling context. For peat and organic sediments, it is particularly important to determine whether the dated material corresponds to the event one is trying to date.

Comparing the results with geomorphological, paleoecological, and archaeological data allows for the construction of a more complete chronology and a better understanding of the evolution of the studied environment.

Patrick Rossetti

Patrick is the director of the Archaeology Department at the CIRAM laboratory. He coordinates projects involving dating, isotopic analysis, and the characterization of archaeological materials, in collaboration with research institutions, museums, and archaeologists in France and abroad (ORCID: 0000-0001-8770-6732).