CIRAM recently dated two pieces of fossilized wood: a “morta” oak and a marsh yew. Both were found buried in the same location, in the Bessin and Cotentin marshes in Normandy (Calvados and Manche). And it must be said that the state of preservation of these two fragments is remarkable! Radiocarbon analyses date the oak to between 4,344 and 4,066 BCE (Before Common Era), and the yew to between 2,027 and 1,778 BCE. Despite being 6,000 and 4,000 years old, respectively, these pieces of wood retain an almost intact structure and appearance.

But how can such excellent preservation be explained? And what do these millennia-old woods tell us about the history of the landscape? Here’s a brief overview of a material that is as fascinating as it is precious.

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

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, archaeological surveys conducted as part of the dredging work on the Brière canals, undertaken by the Syndicat du Bassin Versant du Brivet (SBVB), show that the mortas serve as veritable environmental archives. These millennia-old plants provide evidence of, among other things:

• 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 incorporated into a comprehensive analysis of the region, encompassing both archaeological and paleoenvironmental perspectives. Radiocarbon analyses date the origin of the morta to between the end of the Neolithic period and the beginning of the Bronze Age. It therefore grew approximately 5,000 to 7,000 years ago, in a forested environment that no longer exists.

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 normal 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.

Today, this material is particularly prized for its technical and aesthetic properties. In the past, it was used to build sturdy wooden frames or as firewood. Today, it is no longer sold in its raw state; instead, it is crafted into knives, pens, pipes, sculptures, and 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 – Atelier JHP 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 types of wood from Calvados underwent a long process of fossilization, making them rot-resistant under natural conditions. This anaerobic environment is responsible for their exceptional preservation and their slow transformation into a dense, dark, and stabilized material. As we noted above, carbon-14 dating reveals two periods of burial, even though we found our oak and yew in the same location. We can reasonably infer that there were several phases of rising and then falling water levels. These fluctuations explain the trees’ decline and their gradual entrapment in the peat deposits.

For oak, the black color is obviously not its original color, as it is a wood with naturally light brown hues. It is this particular coloration, evidence of chemical interactions that occurred over millennia in a humid environment, that gives it its aesthetic charm, particularly prized for works of art. Under the same conditions, yew (Taxus baccata) wood has darkened slightly, whereas it is usually a brownish-orange wood.

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 therefore had a large diameter and grew slowly. Consequently, it was an old tree. This observation attests to the plant’s incredible preservation from the time of 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

Finally, the morta oak exhibits particular mechanical characteristics. The mineralization of the wood during its burial was accompanied by a significant change in its density; 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 data sheet published by CIRAD, the density for a sessile oak or a pedunculate oak (Quercus petraea or Quercus robur) is around 740 kg/m³, representing an increase of 31% (source: Quercus robur / petraea technical data sheet).

For its part, our yew underwent an equally spectacular mineralization: measurements taken on six samples yielded an average of approximately 750 kg/m³, whereas the typical density ranges from 480 to 600 kg/m³—representing a density increase of 24 to 56%! This significant increase in density reflects the physicochemical transformations of the wood in a water-saturated, oxygen-deprived environment, which permanently alter its mechanical properties.

A denser wood, but one that is harder 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 Department, 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,” a marsh oak from Brière, is a candidate for PGI status
• L’écho (2025), Brière. Le morta: 10 Things to Know About This Wood That Has Been Buried for 5,000 Years in the BrièreMarshes
• "Quiet, It's Growing! " (2022), Video – Le morta
• CIRAD Tropix, Technical Data 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 Communication & Digital Marketing Manager at CIRAM, Jennifer combines a background in science with a specialization in marketing, communication and event planning. She currently works to promote CIRAM laboratory’s expertise and projects.

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

Learn about their principles, areas of application, limitations, and the criteria for selecting the most appropriate method for each archaeological context.

Three dating techniques, three distinct scientific approaches

Carbon-14

Carbon-14 (radiocarbon) dating is based on measuring the radioactive decay of the ¹⁴C isotope, which is naturally present in living organisms. When the organism dies, the exchange of carbon 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, it is possible to estimate the date of death of the organism.

It is used in archaeology because it provides an average accuracy of ±20 to 200 years. It can be used to date:

Radiocarbon dating applies only to organic materials, which means it cannot be used for ceramics, stones, metals, or mineral sediments. It is also susceptible to modern contamination (bacteria, roots, seepage) that can skew the results. It is therefore crucial to collect samples carefully to ensure reliable scientific dating.

Thermoluminescence (TL)

Thermoluminescence dating is based on measuring the light emitted by a mineral when it is reheated in the laboratory. This technique analyzes the electrons trapped in the material’s crystal structure since its last exposure to high temperatures, typically during its manufacture or use in a fireplace. These electrons accumulate as a result of natural radioactivity in 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.

Thermoluminescence will be used to date:

Thermoluminescence covers a time range of approximately 300 to 500,000 years, with an average accuracy of ±10%.

However, this technique has certain limitations:

• It is destructive: a substantial sample of the material is removed for analysis,
• It is sensitive to potential future warming, whether natural or human-induced,
• It requires precise knowledge of the ambient radioactivity in the environment where the material was buried in order to accurately calculate the age.

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.

For more information: 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—typically quartz or feldspar—when they are exposed to controlled light in a laboratory. This signal corresponds to the accumulation of electrons trapped 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 to date:

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 specialized equipment for sample preparation and analysis, as well as a high degree of rigor in data processing to account for the site’s natural radioactivity. As with other luminescence dating techniques, the reliability of scientific dating depends directly on the quality of the sample, the preservation of the sediment, and the 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 make it easier to compare them.

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: Choosing a Non-Destructive or Complementary Method

However, the context of a study conducted as part of an excavation may involve various elements to be analyzed. Combining these methods often yields a more robust chronology. A specialized laboratory can therefore recommend the most appropriate analyses based on the available materials and the study’s objectives.

Example: on a Neolithic site featuring a hearth, ceramics, and sedimentary layers:

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

In conclusion, the choice between carbon-14 dating, thermoluminescence (TL), and optically stimulated luminescence (OSL) depends primarily on the material being studied, the archaeological context, and the scientific question at hand. These methods are not mutually exclusive; they are complementary and can be combined to refine the chronology of a site or an object.

If you have any questions, CIRAM’s experts will help you select the most appropriate analyses and interpret the results in order to establish a reliable chronology that is consistent with your archaeological context.

Patrick Rossetti

Patrick is the director of the Archaeology Department at 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, every fragment of charcoal can provide valuable information about ancient landscapes and human activities. This is precisely the role of anthracology, a discipline that identifies tree species based on archaeological charcoal. In addition to reconstructing the ancient environment, it helps select the most relevant samples prior to carbon-14 dating. Let’s explore how this discipline helps ensure the reliability of archaeological interpretations.

Understanding anthracology in the context of preventive excavations

Anthracology is a cutting-edge discipline in archaeology, offering 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.

Charcoal found during preventive excavations may originate from hearths, combustion structures, burned building materials, or natural fires. What they all have in common is that they faithfully preserve the anatomical structures of the original wood, which allows scientists to perform an accurate 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 a valuable artifact?

In the context of preventive excavations, charcoal plays a special role. It serves both as evidence of local paleovegetation and as a preferred material for carbon-14 dating. It serves both as evidence of local paleovegetation and as a preferred material for carbon-14 dating (up to approximately 60,000 years).

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

• What were the environments surrounding the excavation site? The study of charcoal allows us to reconstruct the paleoenvironments and wood-use practices.
  
• Which charcoal samples should be prioritized for dating? Criteria include preservation, size, and stratigraphic position
  
• How can we 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 conduct an anthracological analysis before a C-14 dating test?

Selecting datable charcoal samples is a critical step. Some fragments may come from older parts of a tree, which introduces a temporal bias, while other, more recent fragments better reflect the archaeological event under study. Through anthracology, archaeologists can thus:

• Identify the most relevant tree species,
  
• Exclude fragments that could lead to an incorrect date,
  
• 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 is an essential preliminary step in carbon-14 dating. By selecting the charcoal samples most representative of the archaeological context and minimizing the “old wood” effect, it improves the reliability of the dates obtained. Anthracology and radiocarbon dating 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 sample preparation and the observations made in the laboratory. In particular, scientists examine the anatomical structures of the charcoal under a microscope to identify wood species and assess their suitability for dating. Learn how an anthracological analysis is conducted and the criteria observed in the laboratory.

Beyond reconstructing ancient landscapes, anthracology directly contributes to the reliability of carbon-14 dating and the interpretation of archaeological contexts.

Joey Montagut

Archeobotanist specializing in xylology and anthracology at CIRAM

Mass spectrometry is now one of the most widely used analytical techniques in archaeology. It can be used to date artifacts using carbon-14, study the composition of materials, identify organic residues, and analyze stable isotopes to gain a better understanding of ancient societies. Its precision and sensitivity make it possible to obtain information from minute quantities of material.

However, there are several types of mass spectrometry, each designed for 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 artifacts, study their chemical composition, or analyze their isotopic signatures 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 involves ionizing a sample and then separating the ions based on their mass. This allows scientists to identify the chemical elements, isotopes, or molecules present, even when the quantities being analyzed are extremely small.

This sensitivity makes it possible to study valuable or very small archaeological artifacts while obtaining highly accurate results. Depending on the objectives of the study, researchers use different mass spectrometry techniques, each of which addresses a specific research question.

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 a single research project.

Practical Applications: What Mass Spectrometry Reveals in Archaeology

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

Dating Archaeological Remains

Accelerator mass spectrometry (AMS) remains the gold standard for carbon-14 dating in archaeology. Unlike conventional techniques, it allows for the dating of samples as small as a few milligrams with extreme precision through direct measurement of the 14C/12C ratio. It is therefore the method of choice for analyzing delicate objects or those of great cultural heritage value (human bones, funerary textiles, charcoal in sealed contexts). It provides precise archaeological dating while minimizing biases associated with contaminants or sample size.

Reconstructing the Lifestyles of Ancient Populations

IRMS stable isotope analysis opens up a whole new field of interpretation in archaeological contexts. The study of stable isotopes of carbon, nitrogen, oxygen or sulphur makes it possible to trace diets, identify areas of origin, and even distinguish social practices (e.g., identifying diets differentiated by status or gender). 

Identify residues remaining on 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 mass spectrometry offers vast possibilities for archaeology, it nevertheless requires the implementation of rigorous analytical protocols. Sampling must therefore be planned well in advance of the excavation in order to assess the nature of the material, its state of preservation, and any potential risks of contamination. A reliable interpretation depends on close collaboration between the field teams and the laboratory specializing in archaeological analysis.

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. Through its various techniques (AMS, IRMS, GC-MS, and LC-MS), it enables the dating of materials, the identification of their composition, and the provision of new insights into ancient societies. Combined with field observations, these analyses help build a more comprehensive scientific interpretation of the sites. The CIRAM laboratory thus supports professionals in the field of archaeology by implementing these various analytical approaches, tailored to the challenges of preventive, planned, 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.

Les archéologues doivent établir des chronologies fiables pour comprendre l’occupation, l’évolution et les usages des sites étudiés. Cette étape constitue un élément fondamental de leur démarche scientifique. Cependant, du fait de la diversité des contextes, des matériaux et des objectifs de recherche, aucune méthode ne peut, à elle seule, garantir une datation irréfutable.

C’est pour cette raison que les chercheurs adoptent aujourd’hui le croisement de plusieurs méthodes de datation comme approche de référence en contexte archéologique. La combinaison de plusieurs techniques telles que la datation radiocarbone, thermoluminescence, OSL, dendrochronologie, ESR leur permet d’affiner, valider et sécuriser les résultats de leurs études. Pour y parvenir, il leur faut cependant bien connaître les atouts et les limites de chaque méthode, respecter les protocoles et comprendre le rôle déterminant des laboratoires spécialisés. 

Dans cet article, nous vous proposons une revue des techniques de datation en contexte archéologique, un examen de leur complémentarité et l’importance de collaborer avec un laboratoire expert.

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 dating methods, such as carbon-14 dating, thermoluminescence, dendrochronology, OSL, ESR, and U-Th dating, make it possible to assign an age expressed in years. They are applied to a variety of materials, such as organic matter (coal, 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

Chaque technique possède un champ d’application défini, des marges d’erreur spécifiques et des protocoles stricts. C’est précisément cette complémentarité qui justifie leur utilisation conjointe.

Par exemple, la datation carbone 14 est une technique fiable jusqu’à 50 000 ans pour les matériaux organiques, mais elle reste sensible aux contaminations récentes. La thermoluminescence et l’OSL sont quant à elles réservées aux matériaux ayant subi un dernier chauffage ou une exposition à la lumière (céramiques, sédiments), avec des incertitudes liées à la dose annuelle reçue.

Other useful methods, such as ESR or U-Th dating, are suited to specific contexts (enamels, limestone, fossil teeth). Dendrochronology can achieve annual precision when an appropriate reference system is available, but its application remains limited to tree species and regions for which reference chronologies exist.

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 single method, no matter how effective, is sufficient on its own to establish a reliable chronology for the sample being analyzed. Combining different dating methods therefore makes it possible to construct 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 leaching or post-depositional contamination. Parallel use of ESR dating, which is more stable over time, helps to secure historical interpretation. This type of approach (combination) is particularly recommended in complex contexts (caves, disturbed levels, tropical environments), or when the dating of artifacts & archaeological samples must 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-Technical Strategy

The choice of a multi-technique strategy therefore depends on a detailed analysis of the archaeological context, the available materials, and the project’s scientific objectives. A specialized laboratory is involved from the very beginning to guide the collection of samples and determine the most appropriate analytical protocols.

This expertise helps minimize biases related to contamination, the preservation of materials, or the inherent limitations of each method, in order to construct coherent and scientifically valid chronologies.

Drawing on its expertise in radiocarbon dating and the analysis of archaeological materials, CIRAM assists professionals in developing analytical strategies tailored to their specific needs.

Patrick Rossetti

Patrick is the director of the Archaeology Department at 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).

Dating mummies is an essential analysis that allows archaeologists to accurately reconstruct the history of ancient civilizations. Among the various methods of archaeological dating, carbon-14 analysis has become an indispensable tool for researchers. However, its application to mummies often presents methodological challenges such as sample selection, contamination risks, chronological limitations, and the corrections needed to mitigate these risks.

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

Specific features of carbon-14 dating of mummies

Carbon-14 dating is an essential analytical method that helps archaeologists establish the chronology of mummies. However, archaeologists must ensure reliable results, and they face several technical and methodological challenges. Among these, sample selection, contamination, and isotopic biases are challenges that must be overcome.

Type of samples to be analyzed

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

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

Mummy hair is a particularly interesting material for carbon-14 dating because of 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 20 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 harder to date?

Although there is a wide variety of samples that can be analyzed from a mummy, several factors complicate carbon-14 dating:

• Modern contamination: Exposure to recent preservatives (varnishes, resins, bitumen) can skew the ¹⁴C/¹²C ratio measurement.
• Conservation environment: the development of micro-organisms could artificially rejuvenate dating, if they are not strictly eliminated.
• Aging of organic material: poor preservation could prevent the collection of enough material for accurate dating.

A study conducted on the golden mummy of Dunkirk has shown that sample selection and chemical pretreatment were crucial to ensuring the reliability of the results. The process of selectively extracting keratin from the hair thus made it possible to eliminate exogenous materials and obtain a reliable date.

How is a mummy dated?

Reliable carbon-14 dating of mummies relies on a rigorous protocol of sampling, preparation and laboratory analysis. Each step is designed to eliminate possible biases and guarantee optimum 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) to remove modern contaminants.
• Selection of the most reliable fractions: mummified hair is preferred as it offers better resistance to environmental alterations.
• Isotope filtering: analysis of carbon isotope ratios to detect any anomalies.

Laboratory Analysis

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

• Measuring the ¹⁴C/¹²C ratio: gas pedal mass spectrometry (AMS) can analyze very small samples.
• Isotopic bias control: are adjustments to account for natural isotopic fractionation.
• Calibration of results: based on IntCal 20 or SH Cal20 calibration curves, essential for correcting historical carbon-14 fluctuations.

Examples of Mummy Dating

Egyptian mummies: dating burial bandages

The linen bandages that wrap Egyptian mummies provide excellent reliability for carbon-14 dating. A study conducted on mummies from the New Kingdom confirmed that they date to the 18th Dynasty using accelerator mass spectrometry (AMS). This technique allows for the analysis of very small samples, thereby minimizing the impact on the mummy’s integrity.

The study of funerary textiles, conducted notably at El Deir in Egypt, has opened up new avenues for dating mummies. Researchers have thus been able to identify different types of textiles, including new linen bandages and fabrics used in everyday life. This approach, which uses reference material, not only allows for the dating of mummies but also provides information on funeral practices and the social status of the deceased.

A remarkable example is the mummy of Nesi-Khons, which has been dated to 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 with carbon-14 dating.

Andean Mummies: Environmental Challenges

A recent study of mummies discovered in the Argentine Andes employed an innovative approach: researchers conducted a counter-dating analysis by dating the lice nits found on the mummies’ hair. This method made it possible to estimate the age of these mummies at between 1,300 and 2,300 years, while also providing valuable genetic information about the mummified individuals.

Complex Cases: Contaminated Mummies

Some mummies were treated with modern substances during the 19th century. To counteract this contamination and ensure reliable dating, scientists must thoroughly clean the samples before analysis in order to obtain usable results. The case of the mummy of Ramses II perfectly illustrates this contamination issue.

Natural mummies: challenges and opportunities

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

For example, remains preserved in permafrost or peat may have absorbed ancient carbon, which skews the results of carbon-14 dating. In these specific cases, scientists combine several methods in addition to carbon-14 dating—such as pollen or wood analysis—to obtain reliable dates.

Carbon-14 is currently the gold standard for dating mummies. Thanks to rigorous sample preparation protocols and accelerator mass spectrometry (AMS), it is possible to obtain precise dates for various organic materials while minimizing the risk of contamination. When combined with data from excavations, these results provide a better understanding of burial practices, preservation conditions, and the history of ancient civilizations. The CIRAM laboratory employs these methods to support research projects and archaeological studies involving ancient human remains.

Patrick Rossetti

Patrick is the director of the Archaeology Department at 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).