A TimeLine Auctions Guide to Artefact Testing and Validation
June 29, 2023
(Revised from an article first published in 2008)
It is impossible to judge if an antiquity is genuine or not by simply viewing an image. To make a judgement based on image alone is flawed and those that adopt such procedures do so unprofessionally. At TimeLine we employ various methods to ascertain if an item is genuine and in addition we employ a vetting committee of over ten qualified archaeologists and other specialists who meet for several days before every printed catalogue sale. Each of these professionals physically handles and studies all of the objects presented to us for the following auction. We do not accept any item for sale unless this vetting committee is unanimous in its dating and opinion regarding the object’s culture.
The testing and validation of artefacts offered for sale by coin and antiquities dealers is an important aspect of the authentication of antiquities, identifying fakes and forgeries and determining the likely origin. Technicians employed by TimeLine Auctions can deploy a range of techniques to provide information from which we may form an opinion about an object, and this article summarises the operation of the more commonly used ones.
Fakes and forgeries are a persistent problem for collectors and dealers, and the elimination of such spurious pieces from authoritative collections is in the interest of both groups and of the scholarly community. Misidentification of genuine artefacts is another problem. Investigation can be difficult and time-consuming, but is essential if our customers are to buy from us with complete confidence.
Laboratories are constantly seeking to maintain as wide a range of techniques and technologies as possible, therefore the techniques dealt within this guide may represent only a selection from among those actually in use. Many of these techniques are available through our in-house facilities.
Visual Appraisal
This is the first technique we use, and it is often the most useful. After years of studying genuine ancient artefacts, TimeLine’s specialists have developed a familiarity with the objects which helps in detecting when something does not look quite right. If so, we will use one of the following techniques to verify and cross-check.
Optical Microscopy
This technique involves the close examination of the surface of an object under powerful magnification. It is customary to use this as a preliminary exercise before progressing to the other techniques described here. The majority of faking and tampering can be detected using a good microscope and a practised eye. Fake surface patination which has been painted on to mask a repair or to impart a feeling of age to a reproduced object can easily be detected under the microscope. Additionally, genuine ancient objects which have been ‘upgraded’ with the addition of modern inlay to increase their value can be discovered.
Most periods of history have characteristic ‘signature’ technologies which are perhaps not hard to replicate to convince the naked eye, but which are easy to expose at high magnification. Microscopy has a further use in linking items produced from a single workshop. Where a particular tool has a slight deformity or irregularity and evidence for this can be found on several items, it is a reasonable deduction that these were all made with the same tool – and therefore they emanate from a single workshop, or from the hands of a single workman. Microscopy is also used when cleaning objects, to ensure that only adhesions and corrosion products are removed to stabilize the surface, and not the underlying structure. TimeLine Auctions is able to conduct this procedure with our in-house facilities.
Boroscopy
Boroscopy is sometimes called Remote Visual Inspection (RVI). It involves inserting a miniaturized camera into an aperture in the object to discover information about its internal structure. The methods of manufacture used to produce an item can often be determined by this method, and compared with those used on known genuine artefacts of the same culture and period. We are able to conduct this procedure with our in-house facilities.
Chemical Testing
There are several forms of chemical testing which can be used to analyse the surface of an object without recourse to XRF technology. It is commonly used to test surface ‘corrosion products’ to determine whether they are genuine or have been applied later to artificially age the object, and to detect repairs such as metal fractures strengthened with modern solder. We are able to conduct this procedure with our in-house facilities.
Metallography
The technique of metallography is used to determine the internal structure of a metallic object. Corrosion may be removed from the surface by mechanical means, but if the underlying chemical reactions which gave rise to it are not halted, the process will continue at a sub-surface level. This will weaken and degrade the object, and if left unchecked for long enough will result in its complete destruction.
Metallography can often be performed where the surface of an object has been disturbed, without the need for further intrusive operations. It is an extension of optical microscopy which can give information about the composition and distribution of elements within the metal. In the case of copper-alloy material, the proportions of copper to other elements and their distribution within the metal can provide dating information when compared to other objects of the same period and culture. Needless to say, it can also be used to detect modern reproductions and ancient forgeries. Furthermore, the chemical changes which take place over decades or centuries are impossible to reproduce mechanically and where these are present at a microscopic level they indicate ancient metal. Several third party metal specialists offer this service.
X-Ray Fluorescence (XRF)
The XRF process is at the heart of modern metallurgical and elemental analysis. A tiny point on the surface of the object is bombarded with X-Rays at the atomic level, which causes the elements present to fluoresce (glow); the properties of the luminescence can be measured to determine which elements are present, and their relative proportions.
Technical developments in micro-processing have allowed XRF machines to be produced which can be bench-mounted or hand-held, and which can give results within minutes on a computer screen. This has allowed the process of testing to become faster and more efficient, and widened its potential applications. The process is entirely non-destructive and the material to be tested does not need any special preparation. The more sensitive machines can give results expressed as ‘parts per million’.
XRF by itself can only provide information about the material’s composition. Results obtained from an item have to be compared with results from other objects in order to establish with confidence that the item’s composition is consistent with material from a specific period. TimeLine is able to conduct this procedure with our in-house facilities.
Radiocarbon Dating
Radiocarbon dating is used to determine the age of organic materials such as wood, bone, ivory, shell, lacquer and antler. It is most useful on material less than about 50,000 years old; beyond that range, the results are less reliable. Radiocarbon (C14) is a naturally occurring radioactive isotope of carbon, far less common than the stable forms (C12 and C13); all three elements are absorbed by living things through interaction with their environment and through the food-chain. At death, further absorption of C14 ceases and gradually the unstable C14 begins to convert to the stable nitrogen (N14) at a known rate; in essence it takes 5730 years for half the C14 in an object to stabilise, known as its ‘half-life’. Comparison of the measured C14 content of an item with its stable carbon content allows an assessment of its age (i.e. the point at which it stopped absorbing C14 and the element began to stabilise). C14 results have to be adjusted due to variations in the amount of C14 in the atmosphere at given periods. Several third party laboratories offer this service.
Radiography
Radiography (X-ray imaging) can be used to detect the internal structure of an object, and thus to determine whether it is whole or assembled from a number of pieces, whether it has suffered damage (and repair), and whether the construction is consistent with other examples from the originating culture and period. Standard medical X-ray equipment is not usually sufficiently penetrative to be used on archaeological materials. Several third party laboratories offer this service.
Thermoluminescence
Thermoluminescence (TL) is a technique which can be used to date ceramic material. It relies upon bombarding the material with thermal energy to release trapped electrons; the freed electrons recombine with atoms and in doing so emit a photon (light particle). The light emitted by the clay upon heating is measured and compared to known emissions data from calibrated material, so it is possible to deduce the amount of radiation acquired by the material since it was fired. The quantity of radiation divided by a known rate of acquisition per year gives the number of years since the pottery was fired. For this process we use Oxford Authentication Ltd.
Ultraviolet Scanning
Ultraviolet Scanning (UVS) can be used to detect the presence of certain materials on an object’s surface – for example, epoxy or other adhesives used to repair breaks, alterations to the object’s appearance made with chemical dyes, re-touched areas. UVS is non-destructive and can be performed with hand-held equipment so that maximum coverage of complex shapes can be achieved. We are able to conduct this procedure with our in-house facilities.
X-Ray Diffraction
X-Ray Diffraction (XRD) is a technique, similar to XRF above, which can measure the diffraction pattern of a surface and thus supply information about the elements present; it is most useful for comparing surface treatments such as pottery glazes and pigments.
Several third party laboratories offer this service.
Conclusion
We hope that this guide has been useful in explaining some of the techniques we can use to authenticate artefacts we offer through our platform. As time progresses, new techniques become available and existing techniques are refined. TimeLine Auctions strives to keep abreast of current trends in the analysis of antiquities in order to ensure that all of our clients may make their purchases with the utmost confidence.
Brett Hammond
(Revised from an article first published in 2008)
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