The scientific analyses generally used to study gold are particularly suited to issues of material provenance and research into manufacturing techniques. But the art market needs to go beyond these results. We need to use these analytical tools to decide whether gold alloys are ancient or modern.
CIRAM's analytical approach to authenticating gold objects.
CIRAM has developed a methodology dedicated to the authentication of gold objects using optical and electron microscopy. This analytical protocol is based on a multi-criteria approach that combines surface examination to observe tool marks and corrosion patterns, to define the nature of surface deposits and to detect possible ancient or modern chemical treatments. At the same time, the chemical composition of the gold is analyzed by ICP-AES (Inductively coupled plasma atomic emission spectroscopy), quantifying concentrations of major and minor elements (up to 0.1%) and trace elements or impurities (concentrations below 0.1% or 1000 ppm - parts per million). It's important to remember that 1 ppm = 1 mg/kg.
Examination of tool marks and polishing techniques
Examination of tool marks is one of the technical markers of object manufacture and polishing techniques employed. Heterogeneous, multidirectional striations are the result of hand tools, while modern, mechanical tools produce clusters of fine, parallel striations.
The importance of surface deposit analysis
The analysis of surface deposits of sedimentary origin or corresponding to corrosion products will be an important step in establishing the age diagnosis. Indeed, the presence of silver chloride microparticles will indicate deliberate chemical attack, in order to simulate the natural weathering of the material. Alternatively, an amorphous surface deposit of iron and chlorine indicates residues of an acidic solution, such as ferric chloride.
Natural weathering of gold alloys
If electron microscopy of the gold surface reveals micro-pitting, microporosities and alterations at the grain boundaries, this is consistent with natural corrosion processes.
The markers of age and modernity in golds
The bibliography indicates that ancient golds "contain a series of trace elements in significant concentrations, such as PGMs, elements of the platinum group (platinum, ruthenium, rhodium, palladium and iridium), but also lead, tin, bismuth, antimony, samarium, arsenic... These impurities are the result of ancient gold extraction and refining techniques, which were not totally free of them. This is why the presence of trace elements is a marker of age for gold alloys. On the other hand, modern extraction and refining techniques, such as the electrolytic process, ensure very pure gold. The purity of gold, in the sense of the absence of impurities and not its fineness (number of carats), will be an indication of modernity, as will the presence of cadmium. Like aluminum and phosphorus in bronzes, cadmium is considered a formal indicator of modernity. After all, its use in metallurgy only began in the 19th century.
The chemical analysis of a painting involves identifying the materials that make up the paint layer: pigments, binders, varnishes, and mineral fillers. This information provides a better understanding of the techniques used, verifies whether the materials are consistent with the painting’s presumed date of creation, and reveals any restorations or forgeries.
In this article, learn how the materials in a painting are analyzed, what techniques are used, and what these analyses actually reveal.
In summary:
Chemical analysis identifies the pigments, binders, varnishes, and mineral fillers in a painting.
It makes it possible to verify whether the materials are consistent with the work’s presumed period of creation.
When combined with carbon-14 dating and scientific imaging techniques, it helps authenticate paintings.
The results should always be interpreted in light of historical and artistic knowledge.
What Chemical Analysis of a Painting Reveals
Chemical analysis is not limited to identifying pigments. It allows us to study all the materials that make up the paint layer in order to better understand how a work was created, to verify that the materials are consistent with the period in which it was made, and to identify any restorations.
This analysis alone does not always allow us to draw conclusions about a painting’s authenticity. That is why it is generally combined with carbon-14 dating of the supports and various scientific imaging techniques.
Chemical analysis of the pigments provides important chronological information that complements the dating of the support. This study has been facilitated by the discovery of numerous synthetic pigments in the 19th and 20th centuries. For example, the discovery of lithopone white (barium sulfate and zinc sulfide) in 1870 and phthalocyanine green in the 1930s. The use of chromium oxide as a green pigment from 1840 onwards, for example, or the manufacture of titanium white (titanium oxide), which began in the 1920s.
However, these investigations also have their limitations: natural pigments don't provide any real chronological information, as in the case of ochre, which was used for the Lascaux cave paintings and is still widely marketed today.
Binders
Binders ensure that pigments hold together and adhere to the support. Identifying them provides insight into the painting technique used by the artist (oil, tempera, wax, etc.) and can sometimes help confirm the period in which a work was created. Certain modern binders also serve as an indication of restoration or a more recent creation.
Nail Polish
Varnishes protect the surface of a painting and alter its appearance. Analyzing them makes it possible to distinguish between the original layers and varnishes applied during later restorations. It also provides information on the work’s state of preservation and guides the decisions made by conservators.
The main analytical methods used in the laboratory
Depending on the materials present and the objectives of the study, several analytical techniques can be used:
Technique:
What it does:
Optical Microscopy
Examining the layers of paint
SEM-EDX
Identify the chemical elements
Raman
Identify the pigments
IRTF
Identify organic and mineral compounds
GC-MS
Identify binders and varnishes
Most of these analyses are carried out without altering the work. Discover why non-destructive analyses are preferred for the study of works of art.
Some examples of table analysis
One example is the study of a painting attributed to an illustrious painter of the late 19th century, which was carried out in two stages. Carbon-14 dating of the support gave a date compatible with the painter's activity, and pigment analysis led to a similar conclusion, since the pigments detected were known in the 19th century and had been found in other works by this artist. Among the pigments detected were vermilion red, copper arsenate green, zinc white and ochre.
Conversely, analysis of a work dated 1920 revealed that it was a forgery. The presence of rutile titanium white—which was first produced in the late 1940s—was, in fact, a definitive indication of its modern origin.
Finally, the analysis of a 15th-century illuminated parchment proved more complex, as carbon-14 dating had confirmed the age of the support, but the pigments turned out to be modern (lithopone, titanium white, ultramarine blue, cadmium red...). In reality, it was an "intelligent copy" made on old paper. It is therefore essential to combine dating and analysis techniques to detect forgeries.
Chemical analysis is an essential step in the scientific study of paintings. By identifying pigments, binders, varnishes, and other materials, it provides valuable information about a work’s creation, history, and authenticity. Combined with carbon-14 dating and scientific imaging techniques, it offers a more comprehensive understanding of the materials and contributes to a reliable scientific assessment.
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Richard Cheret
Richard holds a master’s degree in chemistry (1999) and a master’s degree in the physics of archaeomaterials (2000) from the University of Bordeaux. In 2005, he co-founded the CIRAM laboratory with Olivier Bobin, and today serves as its co-manager and sales director.
You may be wondering about these questions regarding the analysis of the materials used in paintings?
Why analyze the pigments in a painting?
Pigments can provide valuable chronological clues. Some synthetic pigments were not commercially available until the 19th or 20th century. Their presence on a work believed to be older may indicate restoration or forgery.
Can chemical analysis be used to authenticate a painting?
Not on its own. Chemical analysis provides information about the materials, but its results must be cross-referenced with those from substrate dating, scientific imaging techniques, and historical expertise in order to reach a reliable conclusion.
Do chemical analyses require a sample to be taken?
Some analyses require a micro-sample, taken from a specific area of the artwork. The sample is extremely small and tailored to the objectives of the study in order to minimize its impact on the painting.
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Along with carbon-14 dating, thermoluminescence testing (TL testing) is the most widely used technique for scientifically authenticating art objects. CIRAM laboratories combine thermoluminescence (TL test) with X-ray scanner imaging to detect fakes in authentic works of art. A look back at the methods used by CIRAM laboratories.
Complementary methods for authenticating terracotta works
The development of counterfeiters' techniques, combined with their growing understanding of analytical authentication techniques, means that thermoluminescence and carbon-14 are increasingly necessary, but not sufficient. These dating methods provide an initial chronological assessment of the material's age. However, it is becoming increasingly common for counterfeiters to use old materials, which they then reshape to produce fakes.
Fortunately, CIRAM refines the authentication of your works of art by adding complementary analyses such as X-ray scanner imaging.
Examples of new forgeries and methods for detecting them
Thermoluminescence tests carried out on several samples of this head seemed to indicate that the material was fired around 1000 years ago. However, while the results obtained on the various samples were consistent, their characteristics were sufficiently heterogeneous to arouse suspicion. Thanks to the 3-dimensional vision generated by scanner imaging, we can see that this head is made up of an agglomerate of ancient terracotta shards re-cut and assembled with modern clay. The face has been over-modelled on top of the shards. This object falls into the category of "intelligent fakes". This involves using ancient materials to fool thermoluminescence tests. In this case, only a combination of different methods can detect new-generation counterfeits.
Counterfeiters, reading more scientific publications than one might imagine, have unfortunately become more sophisticated in their methods. Aware that the study of corrosion was becoming a major factor in the analysis of a work, some set about creating forgeries mixing old and modern parts.
Aware of this new trend, CIRAM's laboratories are combining methods to refine their analyses and identify new intelligent fakes.
On the X-ray image below, you can see the old part at the bottom and the modern part made of small metal plates assembled with glue or resin.
To identify these assemblies, it is necessary to X-ray the objects, in order to be able to specify whether they have only been restored or whether they are the result of a modern assembly. Once again, we can see that complementary methods are the best discriminating analytical strategies.
Complementary analyses to detect new forgeries
Thanks to factual data derived from physico-chemical analysis, correlation with accumulated knowledge of the evolution of forms, and techniques to support the quest for authenticity, it is possible to authenticate a terracotta work.
To make a precise diagnosis, our scientists always propose a combination of clues, while remaining aware of the limits of each approach. If certainty is the absolute goal of authentication, it is rarely attainable. However, the detection of a fake will always be more obvious than the certainty of an authentic object. But thanks to our expertise and know-how, the result will always be reliable, objective and relevant.
As with rocks or metal, there is no dating method for glass or enamel as such. But the multi-criteria, multi-disciplinary approach of the CIRAM laboratories enables us to give an opinion on the age of your glass objects.
A precise analytical protocol for studying glass objects
For the study of art objects, the first and most obvious type of marker is the chemical composition of the material. Secondly, CIRAM laboratories observe the passage of time and induced alteration. The composition of materials must correspond to the manufacturing techniques of the time. For weathering, the degradation of materials must be of natural origin.
The chemical composition of glass, the first decisive marker
The chemical composition of glass or enamel is a valuable source of chronological information: vitrifiers, stabilizers, fluxes or pigments, the results already provide valuable information.
The composition of a glass, enamel or glaze can be indicative of an era or civilization. For example, lead and potassium concentrations will indicate whether the glassmaking technique corresponds to the Middle Ages or the Renaissance. The nature of the pigments can identify modern production. Cadmium or chromium date 19th or 20th century glass or stained glass.
Our scientists analyze the chemical nature of the glass and the chromogenic elements present to already provide objective data that our laboratory teams interpret to pronounce on the age of the glass objects.
Glass weathering analysis, a crucial step
The most important part of examining a glass object is analyzing its weathering. A glass object that is hundreds or thousands of years old will have undergone significant environmental alteration, due to humidity, temperature variations and the development of micro-organisms. The degree of weathering provides chronological clues as to age or modernity. Glass weathering depends not only on the environment in which it is stored, but also on its composition. If conditions are highly alkaline, then the silica contained in the glass may be progressively dissolved, leaving a dull surface. Under more neutral, slightly alkaline or acidic conditions, glass corrosion is characterized by the progressive elimination of alkaline ions (leaching), sodium and potassium, as well as certain alkaline-earth ions (notably calcium). These are replaced by water and hydroxide ions, OH-. These processes give the surface an onion-skin appearance (laminated multilayers), which may appear iridescent due to the diffraction of light by this microstructure.
Detecting falsification through the presence of fluorine
On the other hand, if fluorine is detected in altered areas, we're dealing with artificial, modern alteration, i.e. incompatible with an ancient period. In fact, the presence of fluorine is totally abnormal in the context of natural burial or the natural ageing process of glass. Fluorine is not present in natural groundwater, as it reacts strongly with calcium to form insoluble minerals. As calcium is one of the most abundant elements in soils, the possibility of observing certain soluble fluorine ions is extremely limited. This means that fluorine cannot come from environmental pollution.
The presence of fluorine is highly problematic, as it indicates that the object has been artificially altered with hydrofluoric acid or a fluorine-rich compound, in order to simulate glass ageing. This acid is the only one capable of dissolving glass. It cannot be used for cleaning or restoration purposes. Consequently, the presence of fluorine in "weathered" areas of glass is a formal indication of modernity.
Micro-analysis to distinguish between forgeries and original works
Microanalysis remains little-known, as it does not provide direct chronological indicators like carbon-14 dating, for example. However, this technique is the most suitable tool for discriminating between fakes and authentic items, particularly for glass and enamel items that do not lend themselves to direct dating methods. It is important to combine all information to authenticate a glass or enamel object.
The answer is yes, but only partially. We can only date the organic materials it is made of, such as canvas, wood, or paper. We cannot date the pigments, and it is sometimes difficult to date the varnish.
In summary:
Carbon-14 dating is used to date the organic materials that make up the painting, while thermoluminescence dating is used to date materials that have been heated. Pigments, therefore, cannot be dated using these methods.
Dating must be supplemented by material analysis, scientific imaging, and historical expertise.
Combining these methods makes it possible to authenticate works of art and identify counterfeits.
The scientific approach based on materials is transchronological. This method is an essential step in authentication, but it must be supplemented by other scientific analyses. There are two dating methods used by CIRAM laboratories:
Not all materials used in a painting can be dated using carbon-14, as shown in the table below:
Materials used in the painting:
Carbon-14 dating:
Fabric (linen, hemp, etc.)
Yes
Wood
Yes
Paper
Yes
Cardboard
Yes
Ivory
Yes
Varnish
Yes: if they are natural and contain organic matter No: if they are synthetic or mineral in origin
Pigments
No
Why isn't carbon-14 dating sufficient to authenticate a painting?
Please note that the date on a work’s medium does not automatically correspond to the date the work was created.
When studying paintings, various imaging techniques—such as those using natural light, raking light, ultraviolet (UV) light, or infrared (IR) reflectography—complement conventional dating methods. However, one problem remains: how can we analyze materials that cannot be dated, such as the pigments used in paintings?
An anthropological and historical approach to complete the results
Historical knowledge of pigment manufacturing techniques will provide chronological data: the use of chromium oxide as a green pigment from 1840 onwards, for example, or the manufacture of titanium white (titanium oxide), which began in the 1920s. These investigations also have their limits: natural pigments provide no real chronological information, as in the case of ochre, which was used for the Lascaux cave paintings!
How is a painting dated?
Dating a painting begins with identifying the materials it is made of in order to determine which ones can be analyzed. A very small sample is then taken from an organic material, such as canvas, wood, or paper. After measuring the carbon-14 levels and calibrating the results, the data obtained are interpreted by comparing them with pigment analyses, scientific imaging, and historical knowledge.
The principles of carbon-14 dating
Carbon-14 dating measures the time that has elapsed since the death of a living organism. Just as death brings human life to an end, a plant’s life ends when it is harvested. For a painting, this corresponds to the time when the flax or hemp used to make the canvas was harvested or when the tree used for the support or frame was felled.
The principles of carbon-14 dating are based on the instability of the carbon-14 isotope. A living organism contains a constant amount of carbon-14 due to exchanges with the atmosphere (respiration or photosynthesis). When the organism dies, these exchanges with the outside world cease, and the amount of carbon-14 then decreases according to a known exponential rate. Its concentration is halved every 5,730 years. The dating limit is approximately 60,000 years. Beyond that, the amount of carbon-14 is too low to be measured by current techniques.
This revolutionary technique earned its inventor, Willard Frank Libby, the Nobel Prize for Chemistry in 1960.
Carbon-14 variation over time, an important factor to take into account
Carbon-14 dates are expressed in years “Before Present” or “BP.” The “present” for carbon-14 was set at 1950 by Libby. Today, however, these values must be corrected because the concentration of carbon-14 has varied over time due to factors such as solar activity, climate change, and industrial activity. These results are referred to as calibrated results, obtained using calibration curves. These curves allow the BP age to be converted into calibrated date ranges associated with a probability percentage (for example, 450 ± 25 years BP corresponds, after calibration, to the range 1422–1471 AD—with a 95.4% probability).
The onset of industrial activity, for its part, led to a decline in Carbon 14 levels and imposed limits on the precision of measurements. Conversely, atmospheric nuclear testing has led to an artificial rise in Carbon 14 levels worldwide. This makes it possible to obtain very precise dates (up to one or two years) for the second half of the 20th century.
Some examples of paintings dated and authenticated by carbon 14
The following examples illustrate how carbon-14 dating can reveal chronological inconsistencies, but also why it must always be cross-checked with other scientific analyses.
In art history, cases of forgery are common, and it is often through a thorough analysis that inconsistencies have been uncovered. Here are two examples:
A painting by a Russian Suprematist painter, dated 1920, had its canvas support finally dated post 1954.
A Picasso composition proposed for dating in the early 20th century revealed, after dating the paper support, that the paper had been manufactured before 1954, and was therefore incompatible with the presumed period.
Generally speaking, it's much easier to prove that a painting is fake than to establish its authenticity:
The dating of a painting attributed to Van Gogh was carried out in two stages. Dating of the support suggested a date compatible with the painter's activity, at the end of the 19th century. Pigment analysis led to a similar conclusion, since the pigments detected were known in the 19th century and had been found in other works by Van Gogh. These included vermilion red, copper arsenate green, zinc white and ochre. However, these pigments were known and used by all painters at the same time, and even today. The Van Gogh committee, made up of art historians, had to decide in favor of an original work.
Conversely, analysis of a 14th-century illuminated parchment confirmed the dating of the support. As for the pigments, they proved to be modern... It was an "intelligent" copy made before 1950... on old paper. It is therefore essential to combine analytical techniques to detect forgeries.
Richard holds a master’s degree in chemistry (1999) and a master’s degree in the physics of archaeomaterials (2000) from the University of Bordeaux. In 2005, he co-founded the CIRAM laboratory with Olivier Bobin, and today serves as its co-manager and sales director.
You might be asking yourself these questions about dating paintings?
Can any painting be dated using carbon-14 dating?
No. Carbon-14 dating applies only to materials of organic origin. Mineral pigments and most varnishes cannot be dated using this method. Whether dating is feasible therefore depends on the materials from which the artwork is made.
How accurate is carbon-14 dating?
Accuracy depends on several factors: the nature and state of preservation of the sample, the period in which it was produced, and natural variations in atmospheric carbon-14. Results are expressed as calibrated date ranges associated with a statistical probability. For materials dating from the second half of the 20th century, the “bomb peak” method can sometimes achieve an accuracy of one to two years.
Why can't pigments be dated?
Most pigments used in painting are of mineral origin (ochre, azurite, vermilion, titanium white, etc.) and therefore do not contain organic carbon that can be measured using the carbon-14 method. They cannot be dated directly. However, their chemical composition serves as an excellent chronological marker: certain pigments were not produced or used until a specific period, and thus help verify the accuracy of an attribution.
Can carbon-14 be used to detect counterfeits?
Yes, in many cases. If the dating of a canvas, paper, or wooden support is inconsistent with the presumed date of the work’s creation, the hypothesis of a forgery can be substantiated. However, consistent dating alone does not prove a painting’s authenticity. The results must be cross-referenced with pigment analysis, scientific imaging, and historical expertise.
What is the difference between dating a painting and authenticating a painting?
Dating involves determining the age of one or more materials that make up the painting, such as canvas, wood, or paper. Authentication is a much more comprehensive process. It relies on a combination of several approaches: dating, material analysis, scientific imaging, provenance research, stylistic examination, and expertise in art history. Dating is therefore an essential element of authentication, but it is not sufficient on its own.
Up to what age can a painting be dated using carbon-14 dating?
The carbon-14 method can be used to date organic materials up to approximately 60,000 years old. This limit is far greater than the age of the painted works preserved today. In practice, the method is particularly well-suited for studying ancient paintings on canvas, wood, or paper, ranging from the medieval period to contemporary works, provided that the organic materials are sufficiently well-preserved to be analyzed.
Is the sample collection procedure destructive?
Yes, carbon-14 dating requires the removal of a sample. However, the amount of material removed is extremely small, and the sample is taken from an inconspicuous area of the artwork to minimize its impact. Before any work is done, the laboratory works with the owner or curator to determine the most appropriate sampling strategy.
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Above all, it's important to know that works of art must be studied in terms of consistency between constituent materials and chronological attribution. The results of historical and stylistic aspects will have to be discussed by historians, art historians and art experts. In this context, CIRAM scientists are studying the physico-chemical properties of materials in order to search for chronological markers.
For the study of art objects, the first and most obvious type of marker is the search for traces of the passage of time. For organic materials (wood, textiles, ivory, and paper, etc.), CIRAM laboratories favor carbon-14 dating. However, for stone statues, there is no direct dating method that can characterize human use of these materials.
Stages in the study of stone objects
To study stone sculptures, CIRAM laboratories have implemented an analytical protocol to search for relative chronological markers as well as significant technical markers. Discover the two main analysis steps at CIRAM laboratories.
First step: identifying the rock
The first step is fundamental, as it determines the choice of analysis techniques to come. Techniques differ:
For sandstone, limestone and marble: these materials are highly prone to weathering, and microsection studies will provide a binary indicator of their age. Logically, an early carved object will be heavily weathered, while a modern one will still be in good condition.
Magmatic rocks (e.g. granites or diorites): these materials are only slightly altered, so there's no need to investigate the penetration of alteration with a sample. Our scientists then study the surface with minimally intrusive analyses. We recover only a very small amount of material from the surface using surface replicas.
It's important to remember, however, that while it is sometimes possible to determine a rock's geographical origin, this alone is not a definitive indication of authenticity.
Second step: investigating the surface of an object
The investigation begins with the examination of tool marks. These traces are technical markers of the shaping of the object and the polishing techniques used. In some cases, microscopic fragments of tool shavings can be found.
This initial approach enables us to verify the consistency between what scientists observe and our knowledge of ancient know-how.
Any traces of polychromy can be studied to compare the pigments found with those used at the object's presumed time. Residues of burial sediments are sometimes present on the surface of the object.
More specifically, our scientists look for traces of chemical treatments to detect an artificial recreation of the patina in order to simulate stone ageing. The presence of chemical traces produced by the reaction of strong acids with the stone allows the detection of modern surface treatments.
Surface replicas provide information on rock alteration. Dissolution, cracking or amorphization can be detected. We can also detect the recrystallization of iron and manganese oxides, as well as the development of micro-organisms.
To complete our investigation, we also study surface deposits and their interpenetration with the rock. This allows us to verify whether the deposits correspond to burial sediments, reflecting slow interaction with the object or, conversely, modern chemical treatment.
Interpretation of results
Surface investigations provide diagnostic elements and enable us to verify whether or not the indicators observed are compatible with the presumed age of the object.
It is important to note that the investigative methods mentioned above have their limitations:
The presence of modern tool shavings or traces of mechanical polishing does not categorically determine falsification, as these may be traces of cleaning or restoration;
The absence of rock weathering can be explained in several ways. Either the object is actually modern, or it is old, but has been preserved in a stable, non-aggressive environment (such as a sealed tomb). It should be noted, however, that the presence of fluorine is an indisputable indicator of falsification for the purpose of creating an artificial patina. Furthermore, hydrofluoric acid (HF) is a highly corrosive and dangerous product, and its possession is regulated.
Important: it is often easier to demonstrate that an object is fake, than to prove its authenticity, as the slightest inconsistency with the presumed context is enough to induce reasonable doubt. Conversely, failure to detect an inconsistency does not attest to the authenticity of the stone object.
Microanalysis for stone objects
Microanalysis remains little-known, as it does not provide direct chronological indicators, like carbon-14 dating, for example. However, this technique is the most suitable tool for discriminating between fakes and authentic items, particularly for rocks and metals that do not lend themselves to direct dating methods.
It's important to combine all the information in the quest for authenticity of a stone object.
CIRAM laboratories carry out carbon-14 (or radiocarbon) dating of your art objects in wood, ivory, bone, textiles... but also of organic materials in general. Discover CIRAM's protocols for dating ivory objects: dating method, calibration of results and interpretation. Our scientists interpret the results with the utmost precision, so you get the results you expect.
Carbon-14 dating techniques for ivory from CIRAM laboratories
Radiocarbon (carbon-14) dating quantifies the time that has elapsed since the death of an organism. The technique is based on measuring the amount of carbon 14 remaining in an organism after death. 14C is a radioactive carbon isotope that decays progressively according to a known exponential law. Its concentration is halved every 5,730 years. Beyond 60,000 years, the quantity of carbon 14 is too small to be measured. This is the dating limit.
Collagen extraction, the first step to precise dating
Ivory is composed of a mineral part, bioapatite, and an organic part, collagen. Collagen is the most suitable fraction and is normally used for radiocarbon dating. The first step in the dating process is therefore collagen extraction. To this end, samples are treated with hydrochloric acid (HCl, 1 M), then treated with sodium hydroxide (0.1 M) at room temperature and again treated with cold hydrochloric acid, to avoid absorption of atmospheric carbon dioxide. After washing with demineralized water, the samples are boiled to dissolve and recover the collagen.
Collagen analysis, a crucial step in ivory dating
The extracted collagen undergoes combustion at 920°C and is transformed into gas. During this stage, an initial check of the C/N ratio is carried out using an elemental analyzer (Elementar Vario ISOTOPE Select). This step is essential, as it constitutes a quality control. A C/N value between 2.9 and 3.6 indicates that the collagen is well preserved and will provide reliable dating. If the C/N ratio is outside this range, the collagen will not be C14 dated. In this case, the mineral part of the ivory can be used to date the bioapatite. Stable carbon and nitrogen isotope analysis will then be carried out using IRMS. These values will provide information on the terrestrial or marine origin of the ivory. At the same time, carbon dioxide from combustion is separated from other residues using a zeolite trap. This carbon dioxide is then catalytically converted into graphite using an automated system (AGE 3, Ion Plus).
Mass spectrometry for radiocarbon measurement
For radiocarbon measurement, we use Accelerator Mass Spectrometry (AMS). This method requires very little material (1 mg of pure carbon compared with 1g previously), a minimum of time (around 1 hour of counting instead of several days or weeks in the past) and a more accurate result.
Gross age and calibrated dating: the importance of calibrating results
To obtain reliable and relevant data, it is important to calibrate the results based on :
Gross age: expressed in BP years (before present, or before 1954), based on the assumption that carbon-14 concentration has been constant in time and space.
To obtain calibrated dates, calibration curves are used, which take into account variations in carbon-14 content in space and time. These calibrated dates, combined with probability percentages, are used to verify the authenticity of an ivory object.
The problem of recent dating (after 1954)
It is possible to tell whether objects were made before or after 1954 by their carbon-14 content, but how?
This artificial "boundary" was man-made, as atomic bombs and atmospheric nuclear testing in the 50s and 60s doubled the amount of carbon-14 in the atmosphere.
In recent objects, our scientists have detected abnormally high levels of carbon 14. However, since the end of atmospheric nuclear testing in the mid-1960s, we have seen a steady decline in the quantity of C14. This phenomenon makes it possible to provide very precise dating of recent years (to within one or two years in the best case), used for dating wine, for example.
Carbon-14 dating in Tribal Art
Radiocarbon dating is relevant to Tribal Art, because carbon 14 can absolutely differentiate between objects made from materials that lived before and after 1954. Carbon 14 clearly identifies copies and fakes. The analysis is equally effective for older cultures.
But these scientific "tests" must be combined with a historical and stylistic study of a work. It is important to maintain a global and comprehensive approach to deliver accurate and reliable results. Carbon-14 dating must be used as an objective aid to decision-making.
Filing a CITES dossier with radiocarbon dating
Carbon-14 dating of ivory is also useful for filing a CITES dossier, to prove that the animal died before 1947. The 1975 UNESCO Convention restricts the sale and possession of elephant tusks.
Whether for the art market or archaeology, carbon-14 dating is a major advance. Over the years, this analysis has become a precious and indispensable tool for CIRAM laboratories.
Discover CIRAM's thermoluminescence test protocols, measurements and results interpretation.
In summary:
Thermoluminescence allows dating of terracotta, ceramics, and certain porcelain objects.
It evaluates the time elapsed since the last firing of the object.
The pre-dose method can be used for certain porcelains and earthenware that are difficult to analyze by conventional thermoluminescence.
Combined with other techniques, such as X-ray imaging, it contributes to the authentication of ancient objects and the detection of fakes.
The thermoluminescence laboratory test
The dating of materials provides a valuable chronological marker for authenticating a work of art. However, it is necessary to distinguish the dated event from the one we are trying to date: dating a material does not mean dating its use by humans.
Our scientists use carbon-14 dating for organic materials, but we also use other dating methods for inorganic materials. For heated objects, CIRAM uses thermoluminescence, which applies to ceramics, porcelain, and terracotta in general. This method allows us to date objects up to approximately 300,000 years old.
Thermoluminescence does not apply to all materials. For stone, metal, glass, or pigments, CIRAM laboratories can use other analysis methods to help authenticate them.
The phenomenon of luminescence
In 1664, Boyle reported the phenomenon of luminescence stimulated by heat input or thermoluminescence (TL). Scientists began studying its physical properties in the 1930s, thanks to the development of photomultiplier tubes. In the 1950s, they explored the potential of thermoluminescence for dating archaeological materials, particularly ceramics. However, the application of TL to dating only came to fruition around the mid-1960s in England. It wasn't until 1967 that the first TL dating work was seen in France.
The principle of thermoluminescence
TL is based on the study of natural radioactivity and the ability of crystals contained in baked clay to accumulate the effects of this irradiation. In other words, TL corresponds to the emission of light (luminescence phenomenon) caused by an input of energy in the form of heat (thermo). The energy accumulated by the crystals depends on the duration of exposure to natural radioactivity and the intensity of this irradiation. Thermoluminescence makes it possible to estimate the dose accumulated since the last firing of the material.
TL tests are used to determine the natural radiation dose (QNat) received since time zero (i.e. the last time the material was heated). For true TL dating, two values need to be measured:
QNat: actual irradiation dose ;
I: annual radiation dose.
TL dating of objects out of their burial context does not allow for real dating. However, the measurement of QNat will assess the age and provide objective information on the authenticity or not of the studied object. For this, an annual irradiation dose between 3 and 6 mGy/year will be considered, which corresponds to the vast majority of cases encountered. The absence of annual dose measurement limits the accuracy of thermoluminescence dating tests to approximately 20 to 30% of the estimated age.
Distinction between forgeries and authentic objects
The examination of thermoluminescence curves can provide clues about the age of an object and help distinguish an old object from a recent imitation.
Thermoluminescence dates the last significant heating of the material, generally the firing during its manufacture. It therefore does not, on its own, allow dating of the object's use by humans.
The thermoluminescence test
The TL test is relatively simple to perform. However, the diversity of materials makes it complex to adapt measurement protocols and interpret the results.
Porcelain, like earthenware and stoneware, is fired at high temperatures during its manufacture. This heating can lead to partial or total amorphization of the material and alter the crystalline defects that store natural radioactivity energy. The physical properties necessary for classic thermoluminescence can then be modified, making the material difficult to date by this method.
For these materials, laboratories can adapt the measurement protocol. The so-called pre-dose method, particularly suitable for porcelain and earthenware, is based on the study of a low-temperature signal, around 110 °C, with heating that can be limited to 200 °C, compared to a temperature that can reach 500 °C for classic TL.
The evolution of forgers' methods, linked to their growing understanding of analytical techniques, makes the use of TL increasingly necessary to detect fakes. To authenticate works of art, this method can be combined with other investigative techniques, notably X-ray imaging (radiography or CT scan), which provides complementary information on the object's structure.
The quest for authenticity in terracotta objects
Factual data from physicochemical analysis, cross-referenced with knowledge of the evolution of forms and techniques, contribute to the quest for authenticity.
To establish an accurate diagnosis, our scientists rely on a range of clues, while taking into account the limitations of each approach. If certainty is the absolute goal of authentication, it remains rarely attainable. However, detecting a fake is generally more obvious than absolutely confirming the authenticity of an object. Thanks to their expertise and know-how, CIRAM laboratories provide objective and relevant results.
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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).
You may be asking yourself these questions about TL-OSL?
What does thermoluminescence allow to date?
Thermoluminescence allows dating mineral materials that have been heated, such as terracotta, ceramics, and certain porcelain objects. It estimates the time elapsed since their last firing.
Does thermoluminescence make it possible to detect fakes?
Thermoluminescence can help distinguish an ancient object from a recent imitation by estimating the time elapsed since its last firing. To strengthen authentication, it can be supplemented by other analyses, notably X-ray imaging.
What is the difference between thermoluminescence and carbon-14 dating?
Thermoluminescence applies to certain heated mineral materials, while carbon-14 dating concerns materials containing carbon of biological origin. These methods therefore meet different needs and can be complementary.
Can porcelain be dated by thermoluminescence?
Yes. However, high cooking temperatures can alter the material's properties and complicate analysis. The pre-dose method can then be considered depending on the object's characteristics.
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CIRAM laboratories offer carbon-14 dating for your works of art, whether made of wood, ivory, bone, wood, plant fibers... or organic matter in general.
In summary:
Carbon-14 dating makes it possible to date wooden sculptures and other objects made of organic materials up to about 60,000 years old.
Thanks to accelerator mass spectrometry (AMS), the analysis requires only very small amounts of sample.
In particular, this method makes it possible to distinguish between antique works and modern copies and to ensure the authenticity of art objects.
When combined with historical and stylistic analyses, radiocarbon dating provides essential complementary scientific evidence.
How does 14-dating work on wood carvings?
In the late 1940s, American researchers discovered how to use the properties of natural carbon-14 radioactivity to date organic matter. Carbon-14 dating was then exploited by Williard Frank Libby in the 50s on Egyptian samples.
Radiocarbon (carbon 14) dating is used to determine the time elapsed since the death of an organism. This method has revolutionized archaeology, making it possible to date artifacts made of wood, bone, teeth, textiles or even plant macroremains, up to 60,000 years ago.
How does radiocarbon dating work?
This laboratory technique is based on measuring the quantity of carbon 14 remaining in an organism. C14 is a radioactive isotope of carbon that will progressively decrease as soon as the organism dies, according to a known exponential law. It is estimated that the quantity of carbon 14 is halved every 5730 years. However, beyond 60,000 years, the quantity of carbon 14 will be too low to provide a date.
To measure radiocarbon, our scientists use cutting-edge technologies such as Accelerator Mass Spectrometry (AMS). This method is a revolution in the world of dating, since it requires very little material (1 mg of carbon compared with 1g previously), a minimum of time (around 1 hour of counting instead of several days or weeks in the past) and a more precise result.
Calibrating results
To obtain reliable and relevant data, it is important to calibrate the results based on :
Gross age: expressed in BP years, "before present", based on the assumption that carbon-14 concentration has been constant in time and space.
To obtain calibrated dates. We know that carbon-14 content has varied as a function of solar activity, climate and industrial activity. This is why we need to correct and calibrate the raw ages using calibration curves. These calibrated dates, combined with probability percentages, are used to verify the authenticity of a wooden sculpture.
Why were the results different before and after 1954?
It is possible to tell whether objects were made before or after 1954 by their carbon-14 content, but how?
This artificial "boundary" was man-made, as atomic bombs and atmospheric nuclear testing in the 50s and 60s doubled the amount of carbon-14 in the atmosphere.
In recent objects, our scientists have detected abnormally high levels of carbon 14. However, since the end of atmospheric nuclear testing in the mid-1960s, we have seen a steady decline in the quantity of C14. This phenomenon makes it possible to provide very precise dating of recent years (to within one or two years in the best case), used for dating wine, for example.
Is radiocarbon dating relevant to tribal art?
Radiocarbon dating is relevant to Tribal Art, because carbon 14 can absolutely differentiate between objects made from materials that lived before or after 1954. Carbon 14 clearly identifies copies and fakes. Moreover, this analysis is equally effective for older cultures (Dogon, Tellem, Djennenké, for example). Finally, thanks to augmented carbon 14, an innovative method developed by CIRAM and presented in a future article, we can reduce the intervals between the 18th, 19th and early 20th centuries to a few decades.
The place of science in the art market
Whether for the art market or archaeology, carbon-14 dating is a major advance. Over the years, this analysis has become a precious and indispensable tool for CIRAM laboratories.
Carbon 14 dating is particularly useful for detecting fakes in tribal art, for example.
But these scientific "tests" must be combined with a historical and stylistic study of a work. It is important to maintain a global and comprehensive approach to deliver accurate and reliable results. Carbon-14 dating should be used as an objective aid to decision-making, not as an imperative.
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Jean-Baptiste Forget
Head of Fine Art at CIRAM
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