Authenticating Chinese porcelain

To authenticate a piece of porcelain, be it Chinese, the information sought is the age of manufacture of the support material. The most suitable tool for this investigation is thermoluminescence or the TL test. Like all dating methods, it can be used to date an event. In the case of TL, this is the last heat recorded by the material. As a general rule, this will be the firing of the material following its shaping.

The properties of thermoluminescence

The phenomenon of thermoluminescence and its applications have been known and widely described for several decades. Thermoluminescence properties are directly linked to the presence of crystals (mainly quartz) in terracotta. Quartz has the basic chemical formula SiO2. This means that quartz is composed of silicon and oxygen. On an atomic scale, a quartz crystal is a stack of small four-sided pyramids (tetrahedrons) in which there is an oxygen atom at each vertex, and a silicon atom in the middle of the pyramid. The oxygen atoms are shared with the adjacent tetrahedrons. This forms the basis of a perfect crystal. However, this crystal lattice contains defects: gaps, substitutions and the presence of interstitial ions. The existence of these defects is fundamental to TL dating, as they are capable of storing energy. These defects are filled by a steady supply of energy over time. This energy comes from natural radioactivity. As radioactivity is a regular phenomenon, it is correlated with the passage of time. As a result, the more time passes, the more energy is added to the crystals. In the laboratory, we heat the material and record and quantify luminescence (light emission). The amount of light emitted is proportional to the energy stored in the crystals, itself proportional to the time elapsed since the terracotta was manufactured.

Thermoluminescence method detects fake porcelain

Porcelain, like earthenware and stoneware, is fired at very high temperatures during manufacture. This high temperature results in partial or total amorphization (vitrification) of the material. Exposure to high temperatures alters the crystalline lattice, destroying the trapping centers or defects that store radioactive energy. This deprives us of all or part of the information we're looking for, making the material difficult to date by thermoluminescence. However, by adapting the TL measurement protocol, we can date virtually all porcelain. Whereas conventional thermoluminescence heats the material to 500°C, the alternative predose technique only heats to 200°C and focuses on a low-temperature signal at around 110°C.

The predose protocol is really dedicated to porcelain and earthenware, as it is the only way to obtain a date on this type of material heated to high temperature.

The development of counterfeiters' techniques has made thermoluminescence an indispensable tool for detecting fakes. However, as we saw in a previous article, TL tests must be combined with X-ray imaging (radiography or scanner) to detect new fakes.

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.

Our CIRAM laboratories date your tribal art objects using carbon-14 dating, thermoluminescence (TL), and materials analysis.

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The Parcours des Mondes is a major international art fair dedicated to the arts of Africa, Oceania, the Americas, and Asia, as well as archaeology, and is renowned for the quality, diversity, and number of its participants. Every year, in early September, the fair brings together some 50 galleries specializing in these fields in Saint-Germain-des-Prés, in the heart of Paris.

With over twenty years of experience, the Parcours des Mondes is committed to promoting the knowledge and works of the cultures of Africa, Oceania, the Americas, and Asia, and we are delighted to be part of this journey to share this passion with you.

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.

For the sake of precision, it would be more appropriate to speak of tin-rich bronzes, arsenic-rich coppers, or tumbaga (copper-rich gold alloys used in pre-Columbian art).

Metals (especially copper alloys such as bronze) cannot be dated directly. So we have to look for exploitable chronological markers, such as technical clues that can provide indications of the object's authenticity. Our laboratories then interpret the results to authenticate the materials.

CIRAM laboratories, for a global approach to bronze objects

The most relevant approach for metal objects remains the observation and study of the chemical composition of alloys and their degree of corrosion (patina) using optical microscopy and scanning electron microscopy coupled with an elemental analysis system using energy dispersive X-ray spectroscopy (SEM-EDS).

What information is obtained from the chemical analysis of the metal?

The first important piece of information to emerge from microscopy concerns the metal's microstructure. A good understanding of the metal's microstructure provides valuable clues as to how the object was manufactured. For example:

• The presence of dendrites characterizes a melt,
• Flattened, aligned inclusions are evidence of hammering,
• If this alignment is too perfect, it corresponds to a modern laminating process.

Examination of the internal structure can therefore reveal technological clues and, by extension, help to pinpoint the period of creation of the work in question. The same applies to the analysis of alloy composition.

Determining the age of an object by analyzing the composition of an alloy

The study of concentrations of copper, tin, zinc, lead, etc., while not sufficient to determine the age of an object, can be very useful in establishing its modernity.

For example, the presence of aluminum, phosphorus, chromium or manganese (from 0.2 to 0.3%) are formal signs of modernity. Of course, these elements are natural and have always been present on the planet, but their reasoned and deliberate use in the manufacture of metal alloys dates back to the end of the 19th century (and even the beginning of the 20th century for phosphorus).

Indeed, if we refer to the work published by the international scientific community, these elements have never been detected in ancient metals, except in trace amounts (of the order of 0.01%). Furthermore, aluminum cannot correspond to pollution originating from the melt core, for example, as pollution forms inclusions distinct from the metal, and these are not completely dissolved. What's more, aluminum never stands alone in a cast iron core, but is always associated with other elements: silicon in kaolinite; sodium, potassium or calcium in feldspars. So, if you detect 0.5% aluminium in brass, you'd have to detect silicon too, for it to be core pollution. And yet, this is never the case! This proves, if proof were still needed, that the presence of aluminium corresponds to the use of modern metals.

The same applies to phosphorus, manganese and chromium.

Examination for corrosion, or "patina

The final step in characterizing a metal object is to analyze its corrosion.

We usually talk about its patina. While this term implies a surface approach, the study of corrosion focuses in particular on the nature of surface corrosion products (the patina proper), but also on the development of corrosion processes within the alloy.

Why does the study of patina tell us how old an object is?

A copper or silver alloy that is several hundred years old will have been subjected to numerous environmental attacks: humidity, temperature variations, the development of micro-organisms... These elements will lead to the degradation of the metal, its corrosion. Among the most characteristic signs of corrosion of natural origin, developed over several centuries, we can cite the following:

• Deep metal weathering;
• Preferential degradation of copper-rich zones - which are the most fragile;
• Multiple corrosion products (cuprite, azurite, malachite, atacamite, nantokite, tin oxide, etc.), a combination of sediments, or the absence of recurring chlorine or sulfur.

On the other hand, if the corrosion remains very superficial and parallel to the surface of the object, if the metal is attacked homogeneously or if chlorine is detected in all the corrosion products, we can establish that the alteration is artificial and modern. This false patina will therefore indicate that the object has been intentionally degraded, in order to simulate its age.

Finally, it's important to point out that even if an object has been heavily cleaned and its patina removed, microscopic study is still possible. Corrosion processes penetrate the material, leaving traces that even violent abrasion cannot remove.

It is crucial to bear in mind that the study of a metal's chemical composition and degree of weathering provides indirect technical and chronological clues. It is impossible to obtain quantifiable chronological information on metal. Consequently, we cannot tell the difference between an object made 2,000 years ago and one made only 1,000 years ago. These investigations will only enable us to assess the compatibility of the elements studied with the presumed attribution.

CIRAM, a specialist in the dating and authentication of your materials, offers a complete interpretation service. We share our results and discuss their interpretation with you, to explain the relevance of the research, particularly for metal objects.

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 prefer carbon-14 dating. However, for stone statues, there is no direct dating method that can characterize man's use of these materials.

Stages in the study of stone objects

To study stone sculptures, CIRAM's laboratories have set up an analytical protocol enabling them to search for relative chronological markers as well as significant technical markers. Discover the two main stages of analysis 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.

In the demanding market for tribal art, where authenticity and provenance define the value of works, a central question emerges: how do you accurately date "recent" objects dating from the 18ᵉ, 19ᵉ and 20ᵉ centuries? One solution lies in a major scientific breakthrough: augmented carbon-14 dating. Find out in this article how this method reduces the dating interval from 300 to just 40 years, offering an unprecedented solution for tribal art collectors and professionals.

Understanding carbon-14 dating applied to tribal art

Carbon-14 dating is an essential technology that combines scientific rigor with the search for authenticity. Find out more about its fundamental principles and limitations in this section. 

The principles of the carbon-14 method: science and precision

Radiocarbon dating is based on the measurement of the decay of a radioactive isotope present in living organisms, carbon-14. This method was developed in the 1950s by W.F. Libby, winner of the Nobel Prize for Chemistry, and enables organic materials such as wood, ivory and leather to be dated for periods of up to 60,000 years.

However, the traditional Libby method has its limitations: in the past, it required large samples (up to one gram of pure carbon), which severely damaged during sampling. The advent of mass spectrometry (AMS) in the 1980s has since considerably reduced the amount of material required (1mg of pure carbon), ideal for art objects.

Importance of enhanced C14 dating for the authenticity of tribal art

The Suess effect, which limits the accuracy of works dating back 300 years, poses a particular challenge for tribal art. The Suess effect refers to the decrease in carbon-14 levels in the atmosphere due to the massive combustion of fossil fuels since the industrial revolution. This decrease in C14 levels in the air thus affects the accuracy of recent dating. Tribal works, mostly in wood, are often dated from the 18ᵉ to the 20ᵉ century, a period when the classical method is limited by significant uncertainties. 

Visit laboratories specializing in c14 dating dating for tribal art have had to create new methods to counter the Suess effect. CIRAM laboratories have developed a method that combines C14 dating with multidisciplinary analyses to refine the results: augmented C14 dating. augmented C14 dating. Augmented dating reduces, in the best case300 years to just a few decades, enabling a clear distinction to be made between an authentic work and a recent copy.

To achieve this, CIRAM laboratories use an approach based on multiple samples taken from the center to the outside of the wood, enabling the tree's history to be reconstructed. Combined with xylological wood analysis, a method for identifying wood species, estimating tree growth rates and identify the tree's geographical origin..

This approach guarantees a clear differentiation between an old work and a recent copy, meeting the expectations of professionals who demand rigor and reliability when dating tribal artworks. 

Augmented C14 analysis: what benefits for tribal art professionals?

Technological advances now enable far more precise dating, meeting the specific challenges of tribal art professionals and collectors alike. But what are the benefits of this innovative method?

Securing and enhancing the value of tribal artworks

For art collectors and dealers, augmented dating offers a scientific and rigorous guarantee of the authenticity of tribal artworks. This increased precision meets the growing expectations of a market where trust between buyers and sellers is essential.

• Better market value Works accompanied by scientific certificates issued by laboratories such as CIRAM are better perceived by collectors and auction houses. These documents, which attest to the authenticity and precise dating of the pieces, enhance their market value. Buyers are willing to invest more in works that have a verified and scientifically validated provenance.
• Secure transactions Increased dating eliminates areas of uncertainty by guaranteeing the age and origin of works, thus reducing the risk of post-sale disputes. Professionals selling tribal art can thus rely on scientific evidence to defend the authenticity of their pieces in the face of potential buyer disputes.
• Reducing the risk of counterfeiting Enhanced carbon-14 dating actively combats the proliferation of modern copies on the art market, becoming a key tool for distinguishing originals from recent reproductions.

Enhancing the historical understanding of tribal artworks

Augmented dating not only helps to determine the age of works, it also contributes to their historical and cultural contextualization. This multi-dimensional study enriches not only the scientific value of analyses, but also their relevance to art professionals and collectors.

• Analysis of materials Study of and decorative patinas, as well as tool marks can help us to better understand the craft techniques specific to tribal cultures. For example, analysis of a wooden mask can reveal details of the tools and processes used, providing a better understanding of the object's history.
• Knowledge of geographical origins Knowledge of geographical origins: it is possible to trace the ancient trade routes or cultural influences that contributed to the creation of the work by identifying the wood species and analyzing their provenance. This information adds a unique dimension to each piece.
• Detailed cultural narrative Enhanced c14 analysis provides professionals with an enriched narrative, by combining scientific data with historical historical and ethnographic knowledge to present the object to their customers or the public. This narrative, then based on objective resultsreinforces collectors' interest in the work. For example, a Yoruba statuette analyzed using this method could reveal not only its age, but also the environmental context in which the tree grew. the tree's growththe environmental context of the tree's growth, the external influences that marked its creation, and the specific craftsmanship practices of the period.

The historical and cultural enrichment that comes from analyzing a tribal tribal artworks thanks to enhanced carbon-14 dating not only benefits the art market and its players. It also helps to preserve and transmit a unique cultural heritage, while educating the public and art lovers about the importance of tribal objects in world history.

The role of specialized laboratories, such as CIRAM, for tribal art

Specialized laboratories play an essential role in guaranteeing the reliability and integrity of tribal object dating.

CIRAM services: enhanced carbon-14 dating

CIRAM's laboratories do not limit themselves to classical carbon-14 dating. Their expertise extends to a full range of services designed to meet the specific needs of tribal art professionals.

The analyses offered by the laboratory combine several disciplines to deliver reliable results tailored to each object.

• Xylological and physico-chemical analysis By studying the types of wood used, CIRAM scientists can determine not only the type of wood of the woodbut also its geographical origin and growth conditions. This approach enriches our understanding of the objects' history.
• Micro-sampling Micro-sampling: CIRAM's state-of-the-art tools enable micro-sampling to be carried out, preserving the integrity of the artwork. This ensures that even the most fragile objects, such as African wooden masks or ivory sculptures, can be safely analyzed without damaging the work.
• Multidisciplinary studies Multidisciplinary studies: the laboratory combines dating, analytical chemistry, art history and mathematics to cross-reference the data obtained and offer robust conclusions dedicated to tribal art collectors.

Certificates of authenticity and customized support

Working with CIRAM laboratoriesprofessionals or collectors of tribal art benefit from detailed reports and certificates of authenticity, recognized on the art market.. These certificates of authenticity are a major asset in securing transactions in a market where counterfeits are commonplace. They are essential for securing transactions and enhancing the value of works with auction houses, galleries and collectors.

In addition, CIRAM supports its customers in understanding the results and using them to enrich the presentation and enhancement of their works. This advanced level of service, coupled with augmented carbon-14 dating technology, enables collectors, gallery owners or sellers of tribal art to benefit from the best assets to enhance the value of their works for sale. 

Augmented carbon-14 dating revolutionizes the analysis of tribal artworks, offering professionals guarantees of authenticity and provenance. By combining scientific rigor and innovation, CIRAM offers services tailored to market requirements. Relying on precise results and multi-disciplinary multidisciplinary dataCIRAM transforms scientific analysis into a strategic lever for tribal art.

To guarantee the authenticity of your works and secure your investments, call on the CIRAM teams: Request your study today.