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
• L’écho (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).

During preventive excavations, each charcoal fragment can provide valuable information about ancient landscapes and human activities. This is precisely the role of anthracology, a discipline that identifies wood species from archaeological charcoal. In addition to reconstructing the ancient environment, it allows for the selection of the most relevant samples before carbon-14 dating. Let's discover how this discipline contributes to making archaeological interpretations more reliable.

Understanding anthracology in the context of preventive excavations

A cutting-edge discipline in archaeology, anthracology offers preventive excavation teams an essential scientific tool for rapidly interpreting contexts and preparing the dating of remains.

What is anthracology?

Anthracology is a branch of archaeobotany specializing in the study of carbonized wood (charcoal). This method of analysis relies on microscopic observation of anatomical structures, using techniques such as charcoal logging, to determine the species or genera of wood used in archaeological contexts.

The charcoal found during preventive excavations can come from hearths, combustion structures, burnt building elements, or natural fires. All have in common the faithful preservation of the anatomical structures of the initial wood, which allows scientists to perform precise taxonomic 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 serves as both a record of local paleovegetation and a preferred material 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? The study of coals makes it possible to reconstruct paleoenvironments and wood exploitation practices.
  
• Which coals to choose for dating? The criteria include conservation, size, and stratigraphic position
  
• How to avoid bias? Anthracology limits the so-called "old wood" effect, which artificially ages chronologies

The use of anthracology alone cannot restore the entirety of an ancient landscape. However, it is particularly relevant as a complement to other approaches (palynology, carpology, phytoliths). In a preventive context, it remains a tool of choice for orienting analyses and guiding the selection of datable charcoals.

Anthracology and C14 dating: an essential preliminary step

Combining anthracology and radiocarbon dating is no methodological luxury for archaeologists: it's the guarantee of reliable, scientifically usable chronologies for preventive excavations.

Why carry out an anthracological study before C14 dating?

The selection of datable charcoal samples is a critical step. Some fragments may come from old parts of a tree, introducing a temporal bias, while others, more recent, better reflect the archaeological event being studied. Thanks to anthracology, archaeologists can thus:

• Identify the most relevant species,
  
• Discard fragments likely to produce erroneous dating,
  
• Ensure consistency between the stratigraphic context and the dated material.

Incorrect selection of charcoal inevitably has serious consequences: chronological inconsistencies, unusable results and loss of scientific value. Anthracology, when used upstream of a dating study, limits these risks and secures the reliability of established sequences.

Anthracology constitutes an essential preliminary step for carbon-14 dating. By selecting the most representative charcoal samples from the archaeological context and limiting the "old wood" effect, it improves the reliability of the obtained dates. Anthracology and radiocarbon are therefore two complementary approaches: the former selects the most relevant samples, while the latter establishes their chronology.

The quality of the results also depends on the preparation of the samples and the observations made in the laboratory. Scientists, in particular, examine the anatomical structures of the charcoals under a microscope to identify the wood species and assess their suitability for dating. Discover how an anthracological analysis is carried out and the criteria observed in the laboratory.

Beyond the reconstruction of ancient landscapes, anthracology directly contributes to the reliability of radiocarbon dating and the interpretation of archaeological contexts.

Joey Montagut

Archeobotanist specializing in xylology and anthracology at CIRAM

Mass spectrometry is today one of the most widely used analytical techniques in archaeology. It allows for dating remains using carbon 14 as well as studying the composition of materials, identifying organic residues, or analyzing stable isotopes to better understand ancient societies. Its precision and sensitivity make it possible to obtain information from minute quantities of matter.

However, there are several types of mass spectrometry, each serving specific purposes. In this article, we explain how they work, their main applications in archaeology, and the information they can provide.

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 residues left 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.

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).