Rare Collections

Our Proprietary Technology – Examples

Scientific Investigation, Authentication, and Research
(with special emphasis on ceramics, metals, and stone – both ancient and historic)

  • CT scanning (medical and industrial), post processing, digital imaging, and analysis of ceramics, wood, stone, and metals
  • XRF (X-ray fluorescence) elemental analysis - we own the advanced Bruker handheld XRF system
  • X-ray inspection and analysis (digital and film)
  • TL (Thermoluminescence) dating - Oxford Authentication authorized representative
  • Carbon 14 and accelerator mass spectrometry (AMS) dating
  • Metallography, corrosion/alloy analysis, isotopic analysis, and Pb-210 testing
  • FTIR (Fourier Transform Infra-Red) and Raman spectroscopy
  • LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry)
  • Materials characterization testing and pigment identification
  • Microscopic, macroscopic, and borescopic examination
  • Surface deposits, use-wear, and weathering analysis
  • Stable isotope analysis
  • Ultra-violet and infra-red analysis
  • Wood identification and dendrochronology
  • Provenance, documentation analysis, and research

  • The Authentication Process and Methodology

    Expert Witness

  • Strategy and standards for authenticity challenges and defense
  • Critical review of analysis, evidence, and expert reports
  • Authentication methodology

  • Outreach Services

  • Presentations and lectures
  • Seminars and workshops
  • Individual and corporate training

  • Conservation and Restoration Services

  • Conservation - analysis, cleaning, stabilization, research, and documentation
  • Photography - descriptive, scientific, microscopy, ultra-violet, and infra-red
  • Restoration - reassembly, reintegration, research, and documentation

  • Photography, Imaging, and Video Services

  • High-resolution digital photography
  • High-resolution digital scanning
  • High-definition video
  • Scientific, microscopy, ultra-violet, and infra-red

  • Technical Services

  • Web Site, Software, and Database development
  • Intellectual property rights management
  • Hardware sizing and selection
  • Remote systems administration

  • Paleontological Services

  • Research - identification and description
  • Conservation - analysis, cleaning, stabilization, research, and documentation
  • CT scanning, post processing, digital imaging, analysis, and stereolithography / 3D printing
  • X-ray inspection and analysis (digital and film)

  • More Examples, Supplemental Content, and Errata


    Verlag Philipp von Zabern

    Our Latest Publication: Original - Copy - Fake? (hardcover)
    My contribution provides detailed coverage of: scientific analysis of African terracotta’s (as well as Asian examples), TL testing,
    CT scanning, UV and Infra-red analysis, and the Authentication Process with numerous illustrations.

    Purchase the book "Original - Copy - Fake?"
    We have copies in stock! - Please email us for details


    International Symposium Examining the Authenticity of Ancient Works of Art
    Focusing on Bronze and Terracotta Objects from Africa and Asia


    Rare Collections
    5865 Neal Avenue North, Suite 345
    Stillwater, MN 55082 USA
    612-961-4747
    mark@rare-collections.com


    Email Rare Collections

    Copyright 2013 - Rare Collections - All Rights Reserved

    Scientific Investigation Forensic Authentication Expert Witness Analysis and Research of Art and Archaeological Material Services Include CT Scanning XRF and Materials Analysis of African Asian Chinese Pre-Columbian Native American Cycladic and Oceanic Art Ceramics Metals Wood Stone African Art Tribal Art Asian Chinese Pre-Columbian Native American Cycladic Oceanic Art Ceramics Terracotta Metals Wood Stone Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Setting the Standard for Due Diligence Scientific Techniques in the Authentication Process Mark Rasmussen Rare Collections Rare Collections 5865 Neal Avenue North Suite 345 Stillwater MN 55082 USA 612 961 4747 mark@rare-collections.com www.rare-collections.com Introduction The author has recently been engaged in an extensive study of over 200 Nok Katsina and Sokoto terracotta figures imported over a fifteen year period. These objects were acquired from more than 40 dealers and variously tested by four thermoluminescence (TL) testing labs. Support of Legal Proceedings and Lawsuit Defense Support Fraud Investigation TL Testing TL Dating C14 Macro Photography In addition to studying the objects themselves more than 400 TL reports were analyzed. Nok Research A variety of scientific techniques were employed including computed tomography (CT) computed radiography (digital X-ray) microscopy UV and infra red analysis and petrography. An extensive survey of relevant literature was also conducted. The intent of this article is to present an overview of some of the issues and advanced scientific techniques that are currently being used to evaluate these types of objects. In addition a number of traditional techniques are mentioned and discussed within the greater framework of the Authentication Process. The Authentication Process The following is a description of the Authentication Process that documents the minimum standards that must be considered when evaluating objects. However it is clearly recognized that constraints exist when evaluating any object. www.artauthentication.com The availability of information expertise and analytical methods equipment as well as financial and time constraints invariably dictate how far any process can be taken. With that being stated a best practices approach with minimum applicable standards must be the starting point of any evaluation. Constraints must be clearly identified and disclosed as early in the process as possible to appropriately manage and set expectations. Upon completion of the evaluation process these constraints must again be clearly disclosed and ultimately govern the veracity and reliability of the final determination. Process Overview The process of authentication involves many distinct steps that are intimately linked and completely interdependent. The initial steps evaluate the provenance of an object the paperwork that documents it and any prior conservation or analysis efforts. Other steps evaluate the object itself on the basis of artistic qualities stylistic norms variations techniques and materials. Further steps include comparatives research and the identification of applicable analysis techniques. Authoritative Sources must be identified and consulted. Research into the potential for and frequency of forgeries within the relevant areas must also be completed. All of this information is then analyzed to guide the scientific analysis process which further supports or casts doubt on authenticity. It should be noted that scientific testing alone can rarely establish if an object is authentic inauthentic definitively (although it is often useful in detecting fakes alterations and damage). Similarly no single step in the Authentication Process is generally conclusive. Provenance Research The first and most important step in evaluating the authenticity of an object is a rigorous evaluation of its provenance and documentation. Although this process is often difficult it is essential to establish the complete history of the object in order to support the authentication and dating processes. This information should include the exact date location and circumstances of the object s collection and the identity of the collector supplemented by a complete history of the object through the chain of ownership. Provenance that cannot be reasonably verified or is completely absent may cast serious doubt on an object s authenticity and will push the onus of verification onto other aspects of the process that ultimately may not be able to determine the authenticity. It should be clearly noted that there are instances where objects are both scientifically consistent and stylistically correct but are fakes. In some circumstances it all comes down to provenance. Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Conservation History A formal Condition Report prepared by a qualified Conservator is a standard requirement and typically serves as the starting point of any evaluation. If an object has been conserved restored or previously the subject of analysis it is critical that this work is thoroughly documented and that the documentation accompanies the object through the chain of ownership. For example some conservation treatments and analysis techniques (e.g. computed tomography radiography etc.) may alter the effectiveness or completely limit the ability to perform certain authentication and dating procedures. In addition some materials that are routinely used during the course of conservation or cleaning may falsely (or sometimes correctly) be interpreted as signs of fakery or alteration. Authoritative Sources The identification of Authoritative Sources is a critical step in the Authentication Process. Authoritative Sources are represented by three categories Recognized experts Experts at analyzing the object in question must be identified and consulted. The qualifications of these individuals must be carefully reviewed and should be able to withstand reasonable scrutiny multiple experts in each area should be consulted. Reference materials Reference materials that support the analysis process need to be identified and reviewed. Peer reviewed scientific journals and scholarly textbooks are typically excellent resources. Publications that illustrate unprovenanced objects or objects that have not been appropriately studied must be avoided. Web references that can not be definitively tied back to Authoritative Sources must also be avoided. Typically a diligent review of scholarly literature and its accompanying references or bibliographies will identify the appropriate resources. Reference collections Reference collections provide the basis for comparative studies and should be identified. These collections must contain well documented and authentic objects with a solid provenance. Collections that also include inauthentic or altered objects with well documented records on how they were identified detected may also be helpful. Preliminary Research Preliminary research begins by utilizing the full complement of Authoritative Sources including experts in the field (art archaeology science etc.) who have a solid background in analyzing the specific type and style of the object in question. This collective knowledge and research will define which analysis techniques should be employed and will become the basis for the evaluation and interpretation of results. Scientific Research Applicable analysis techniques Every object presents its own unique set of requirements for analysis. Authoritative Sources must be consulted to guide in the selection of appropriate analytical techniques. Wherever possible multiple techniques should be utilized to confirm results and conclusions. Testing techniques that might impact or limit future analyses need to be carefully considered before use. One potential issue may be the lack of consent for analysis methods that affect the object e.g. taking required samples CT scanning radiographs etc. In instances where the owner will not allow the object to be thoroughly tested and where this type of testing is the only means to help authenticate the object no determination can or should ever be made. Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Scientific analysis Analyses should be performed by qualified individuals observing all of the protocols and quality standards appropriate to the techniques employed. The report for each test performed should not only document the findings and conclusions (with appropriate descriptions) but should also document the equipment and methods employed to produce the results. The limitations of the method including any exposure to fakery must be fully explained. Critical to this process is the ability to differentiate natural vs. artificially induced effects. If an attribute is found to be consistent with authenticity but cannot be differentiated from effects that can be artificially (or otherwise) created it cannot be given the same weight and must be considered inconclusive. However the issue of differentiation must not discourage appropriate analysis as most testing is geared toward the identification of attributes that are known to be inconsistent with authentic examples. Rigorous testing should always attempt to eliminate as many inconsistent attributes as possible thereby increasing the confidence (but not proving) that the object is authentic. Again Authoritative Sources must be consulted to guide in the selection of the appropriate and applicable analytical techniques. In addition the precision and detection limits of the techniques and equipment must be fully disclosed. The standard that should be applied to the testing report is that it must contain sufficient detail to facilitate auditing by a qualified third party who could verify the methodology technique results and interpretation. Reports that do not establish applicability (of the testing technique) or fail to relate results to established standards should be considered invalid. Reports that offer data or conclusions with no explanation of how they were derived must also be considered invalid. The final step in the scientific analysis process is to work with Authoritative Sources to interpret the results of the analysis testing correctly and accurately compare them with definitive sources and or statistically relevant expected norms. Please note All of the scientific analysis techniques presented later in this paper would (if applicable) only be small elements of the larger Authentication Process. Final Determination The final step in the Authentication Process is to make a determination. The determination must be made by a qualified individual capable of interpreting and weighing all of the available evidence as produced by the various authentication steps. An important aspect is to determine whether enough data exists to support a determination. A determination of authentic should never be made on the basis of a lack of evidence to the contrary. The evidence needs to support authenticity. In instances where results can be considered ambiguous or inconclusive they should be stated as such with no finding of authentic. Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Thermoluminescence Dating TL dating is an important (and often misunderstood) scientific technique that is applicable to such materials as pottery (baked clay objects) porcelain burnt stone burnt flint and volcanic products. The basic principle is that certain minerals (mainly quartz feldspar and zircon) essentially record the passage of time through the cumulative effect of prolonged exposure to the weak flux of nuclear radiation emitted by radioactivity in the surrounding burial soil and within the object itself (there can also be a small contribution from cosmic radiation). This clock is reset to zero during the firing process (if sufficiently heated) and will subsequently be indicative of the time since the last firing heating. TL testing can also be used to date casting cores (e.g. inside Benin brasses) as well as fired objects that may not have not been buried and the accuracy and limitations of each context must be fully understood. TL testing is performed by having a qualified conservator (trained in TL sample taking) collect (typically by drilling) an appropriate number of samples from the object and submitting them to a TL laboratory for testing. Making sure that the samples are representative of the object as a whole and that they are not contaminated is critical to the process. Forgers are aware of TL testing procedures and often place ancient authentic fragments where they feel sample takers will be most likely to take samples. CT scanning when combined with TL testing is considered the most thorough and accurate method of evaluating valid TL sampling locations. Specific TL Testing Issues Many supposedly ancient ceramic objects have been determined to be fake pastiche objects constructed from age appropriate authentic fragments (often unrelated) combined with various fill materials. This fill material is frequently comprised of age appropriate authentic material that has been ground up and mixed with binders adhesives in an attempt to simulate the original ceramic. The rationale for using ground up age appropriate authentic material is that it will create a similar look and may still pass a TL test if the laboratory does not screen the samples for binders adhesives. This issue is further complicated by the fact that samples that contain binders adhesives are not necessarily problematic it is common to find objects that have been stabilized with binders adhesives during the normal course of conservation. Interpreting the intent and context is the real issue. Some TL reports mention the fact that adhesives binders are present but still provide a date for the samples and leave it up to the reader to guess at the intent context and meaning. In some instances the report will mention that this is normal routine and may further minimize the issue. Objects with this type of notation on the TL report always require further evaluation and testing. The next major challenge is that age appropriate authentic materials are often strategically placed (pastiche objects) where the TL sample taker is most likely to take samples. There are many potential issues associated with TL testing. Specifically TL samples are rarely taken from important locations (such as the face) or from highly decorative areas in order to avoid potential damage. These locations are often the areas that contribute significantly to the value (monetarily historically) of the object. Restoration to these areas is common many featureless or highly damaged objects are enhanced and although they may be real in a general sense the original aesthetic has been changed. The repair of a TL hole is typically a very minor procedure by a qualified Conservator and unwarranted concerns should not discourage appropriate testing. Often the surfaces of objects are obscured by clay slip mud (which may be mixed with binders adhesives) or even completely painted. This issue can make site selection for TL sampling very difficult and often leads to results that are not representative of the object as a whole. Some TL labs charge according to the number of samples to be tested and have an additional charge to screen samples for binders adhesives. This often results in an inadequate number of samples being taken. Samples should be obtained and thoroughly screened (for binders adhesives) from every significant portion of the object especially from areas that contribute significantly to its value (monetarily historically). This sampling should be undertaken only by a fully qualified Conservator and must be considered in light of other techniques such as CT. This creates a bit of a challenge while CT can illustrate the exact condition and composition of the object and can serve as a guide in taking accurate TL samples it is not commonly performed first. While it is true that CT can contribute to the radiation dose of the object testing has demonstrated that it does not normally alter the TL dates produced owing to the low levels of radiation used and the relatively Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved low precision of TL. The minimal risk associated with this radiation exposure can be further mitigated by reserving samples prior to CT scanning and including an appropriate dosimeter with the object during the CT scan then providing a record of the radiation dosage to the TL lab with the samples. This procedure must be done with the prior consent cooperation and guidance of the testing laboratory and its limitations must be fully understood. Most TL labs do not routinely screen samples using Fourier transform infrared (FTIR) spectroscopy or other sophisticated screening methods to check for binders adhesives. They typically must subcontract (at the client s request) for this analysis and additional charges and sampling requirements are necessary. Some contaminants may reveal themselves by their effects on the TL glow curve but not all are so easily detected. This can create a further problem in that some TL labs rely solely on the presence of residue after evaporating the acetone used during sample preparation to detect binders adhesives. This method may only detect binders adhesives that are immiscible with acetone or have discernable amounts of solids. Although this technique may be useful when residue is actually found it is generally considered inadequate. In the event that binders adhesives are detected the challenge of interpreting their presence context remains. One further drawback of TL testing is that it cannot reveal whether the features of an object (or the entire object) have been recently carved from age appropriate authentic material. Featureless and highly damaged objects are sometimes enhanced in this way a common example of this (seen in altered fake Nok figures) is the carving of new eyes into a highly eroded face. The addition of incised and enhancing elements is a further problem. Another example is when decorative elements made from age appropriate authentic material are added to the object. This is generally accompanied by a unifying wash of clay slip mud over the entire surface to obscure the issue. Again these elements objects may TL date correctly but are inauthentic. One final area of fraud that can cause TL to report misleading results is artificial irradiation. In principle the apparent TL age can be increased by exposing the object to a calibrated dose of ionizing radiation. The problem of artificial irradiation is sometimes detected by suspect TL glow curves or anomalous dates although independent testing has proven that it can go undetected. With that being said the artificial irradiation issue may be more prevalent than we currently appreciate. Fake (modern) bronzes brasses that have had their casting cores artificially irradiated have been seen to produce seemingly ancient and valid TL dates. There has been research into methods that have the potential for detecting artificial irradiation (the zircon technique etc.) but routine TL testing does not typically include them. Additional TL Testing Issues Further problems with TL include the frequency of forged or altered TL lab reports. Although some alterations issues concerning these documents are easy to detect some require forensic document examination techniques to discover. It is always advisable to secure a certified copy of the original TL report (with its original photograph) from the issuing lab. Verifying the photograph (with the report) is an important element as the deliberate mismatching of photos and reports is a known fraud technique. Another complication of TL is that it sometimes produces a date that indicates age but does not fit into generally accepted or statistically relevant norms for the material. In these cases other techniques should be employed to further evaluate the object no one should ever simply rely on the fact that it appears old. Analysis of Nok Katsina and Sokoto TL reporting frequency of dates ranges reported. The red bars represent a distribution of the individual years occurring within the TL range reported (as all dates within the range have an equal probability of being correct). The green bars represent a simple distribution of the dates that were specifically reported with a figure. Analysis of Nok Katsina and Sokoto TL accuracy frequency of values reported. Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved All TL labs are not created equal. It is very important to work with a lab that that is recognized for its reputation and experience. Some TL labs may not have the skills necessary to fully evaluate samples and deal with the complex technical issues all too common with potentially forged altered objects. Further labs that allow unqualified sample takers to submit samples or labs that do not have controls in place to deal with fraud chain of custody and quality control issues must be avoided. Examples of probable TL sample taker fraud the figures appear to be pastiche objects. These objects are typically comprised of unrelated age appropriate fragments and restorative materials. The intent of this deception is to create seemingly valid TL reports that falsely support the authenticity of the objects. (the white boxes with X s appear to communicate the planted hidden locations of ancient material) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Computed Tomography (CT) The use of CT in the examination of archaeological material is not a new concept it has been routinely used for many years in the study of everything from Egyptian mummies to fine art objects. Recent advances that have brought this technique to the forefront are the incredible levels of detail that the current generation of CT scanners are capable of producing and advances in computer imaging software that enable advanced analysis of the objects and data. Features as small as .05mm can be visualized with state of the art CT scanners and this combined with the ability to differentiate materials composition density construction and methods of manufacture have made this the technology of choice for serious researchers. These advances have become available at a very opportune time since the number of inauthentic objects and the difficulty in detecting them have presented serious challenges to the art and archaeological communities. The following series of illustrations demonstrate the capability of CT analysis and further underscore the issues that arise when objects are evaluated by TL testing alone (which is never recommended). Fake Nok figure 1. The figure is a pastiche comprised of age appropriate material prior TL testing provided no indication. The surface has been heavily coated to conceal the various unrelated fragments and restorative materials. Please note that this object is a fabrication and is not merely a real Nok that has been restored. (Left photograph Right 3D CT transparent volume reconstruction) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Nok figure 1. (3D CT transparent volume reconstruction various angles) Please note The scope of this article does not allow for the inclusion of sufficient detail to explain all of the analysis behind the CT illustrations. With that being said the following information is intended to provide a basic overview. CT analysis begins with a detailed knowledge of what the interior of objects should look like (and how the various attributes are characterized by CT). This insight typically comes from the prior analysis and study of fragments objects that were properly excavated combined with the knowledge and experience of art historians archaeologists conservators and scientists. A thorough understanding of the materials usage and fabrication techniques appropriate to the type of object is essential. Attributes like the temper grog (coarse inclusions) are evaluated in terms of size density orientation and distribution within the fragments object. The relative thickness and density of each section fragment is carefully considered. Any areas of discontinuity or abrupt change (especially at breaks) are diagnostic. The character of ground up material mixed with binders adhesives and other restorative materials must be recognized. In addition the numerous technical issues specific to CT scanning must be considered as they directly affect the acquisition and interpretation of data. For example spatial resolution constraints detection limits equipment calibration and issues such as beam hardening may all cause data to be misinterpreted if not fully understood. All of these factors (in addition to others) go into the analysis of CT data. Please consult the further reading section of this article for more information. Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Nok figure 1. (sagittal and coronal slices illustrating the use of restorative materials and unrelated fragments) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Nok figure 2. The figure is a pastiche comprised of age appropriate material prior TL testing provided no indication. The surface has been heavily coated to conceal the various unrelated fragments and restorative materials. Please note that this object is a fabrication and is not merely a real Nok that has been restored. (Left photograph Right 3D CT transparent volume reconstruction) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Nok figure 2. (3D CT transparent volume reconstruction various angles) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Nok figure 2. (sagittal and coronal slices illustrating the use of restorative materials and unrelated fragments) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Nok figure 3. The figure is a pastiche comprised of age appropriate material prior TL testing provided no indication. The surface has been heavily coated to conceal the various unrelated fragments and restorative materials. Please note that this object is a fabrication and is not merely a real Nok that has been restored. (Left photograph Right 3D CT transparent volume reconstruction) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Nok figure 3. (3D CT transparent volume reconstruction various angles) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Nok figure 3. (sagittal and coronal slices illustrating the use of restorative materials and unrelated fragments) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Nok figure 4. The figure is a pastiche comprised of age appropriate material prior TL testing provided no indication. The surface has been heavily coated to conceal the various unrelated fragments and restorative materials. Please note that this object is a fabrication and is not merely a real Nok that has been restored. (Left photograph Right 3D CT transparent volume reconstruction) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Nok figure 4. (3D CT transparent volume reconstruction various angles) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Nok figure 4. (sagittal and coronal slices illustrating the use of restorative materials and unrelated fragments) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Nok pastiche objects comprised of age appropriate material. The surfaces been heavily coated to conceal the various unrelated fragments and restorative materials. Please note that these objects are fabrications and are not merely Nok figures that have been restored. (photograph and 3D CT volume reconstructions illustrating the analysis and composition of each object) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved An authentic Nok figure the figure is in three sections and is shown prior to conservation. (Left photograph Right CT sagittal slice illustrating the clay body and interior of the figure) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Various Nok Katsina and Sokoto figures illustrating the variety of objects reviewed during the study. (3D CT transparent volume reconstructions) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved An authentic Tang horse photograph 3D CT image. This image combines the photograph (for identification purposes) with the CT data illustrating the restoration. (photograph 3D CT transparent volume reconstruction highlighting minor repairs) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Fake Han pastiche horse probably comprised of ancient material. The object was made from multiple unrelated fragments and restorative materials concealed beneath a layer of clay and paint pigment. The object was not selected for TL testing as any results would be misleading. (3D CT transparent volume reconstruction) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Tang pastiche horse (the head and body are unrelated) prior TL testing provided no indication. (3D CT transparent volume reconstruction highlighting unrelated element) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Infra red Analysis Direct infra red (IR) reflectance photography utilizing monochromatic as well as full spectrum lighting techniques with various lens filters has been widely used in the scientific examination of artwork for many years. Many materials reflect IR and the degree of reflectance may differ greatly from one material to another even though visually they may appear very similar. This property of differential reflection can be very useful in characterizing materials and detecting surface accretions deposits as well as highlighting areas of wear damage or restoration. IR can often penetrate old varnish and other coatings to reveal masked details. In addition IR can be used to differentiate inks and potentially uncover erased worn or overwritten writing markings on grimy blackened aged or burned surfaces. Djenne pastiche figure (the head and body are unrelated) prior TL testing provided no indication. (Left photograph Center infra red photograph Right CT sagittal slice) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Nok pastiche figure (the head and body are unrelated) prior TL testing provided no indication. (Left photograph Right enhanced infra red photograph) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Ultra violet Analysis Direct ultra violet (UV) and UV fluorescence examination and photography have long been standard tools in the examination of artwork and in the field of forensics. UV fluorescence is often used in mineralogy for identification purposes and can be used to identify metal traces. Many adhesives fluoresce under UV light revealing repairs coatings and the prior location of labels. UV fluorescence may be able to reveal hidden writing markings on surfaces. Weathered original surfaces sometimes fluoresce differently than new or freshly exposed surfaces. Different areas of the UV spectrum can reveal different characteristics and each of the primary wave lengths should be utilized namely long (351 or 368 nm peak) medium (312 nm peak) and short (253.7 nm peak). These light sources should be filtered to remove as much visible light as possible and appropriate UV absorbing safety glasses should always be worn. Fake stone panel from India illustrating artificial patina breakage (above the knee) and enhancements. (Left normal photograph Right 253.7 nm photograph) Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Copyright 2009 Mark Rasmussen Rare Collections All Rights Reserved Conclusion Techniques like CT scanning when accompanied by a thorough examination by a qualified Conservator and the appropriate scientific testing methods can establish the condition character of an object with a high degree of accuracy. This level of scientific certainty when combined with the full Authentication Process a solid provenance and the knowledge of a qualified and experienced art historian and or archaeologist can contribute to a more complete understanding of objects. Further Reading The high level overview provided above is of course just that and as such may be inadequate for a complete understanding of each technique. For those inclined to know everything (or at least more) the following texts make up the body of research from which these methods have been gleaned. Contained within are detailed descriptions of all of the analytical techniques discussed in this paper as well as references that expand on issues specific to the types of objects illustrated. In addition authoritative references are included that provide insights into the archaeological scientific and historical research associated with Nok Katsina and Sokoto figures. Aitken M. (1985). Thermoluminescence dating. London Academic. Aitken M. (1990). Science based dating in archaeology. London Longman. Baruchel J. Buffiere J.Y. Marie E. Merle P. Peix G. (2000). X ray tomography in material science. Paris Hermes Science. Bradley D. Creagh D. (Eds.). (2006). Physical techniques in the study of art archaeology and cultural heritage volume 1. Amsterdam Elsevier. Buchanan M.S. MacLeod W.N. Turner D.C. (1971). The geology of the Jos Plateau. Geological survey of Nigeria bulletin 32 volume 2 younger granite complexes. Calvocoressi D. David N. (1979). A new survey of radiocarbon and thermoluminescence dates for West Africa. The Journal of African History 20(1) 1 29. Ciliberto E. Spoto G. (Eds.). (2000). Modern analytical methods in art and archaeology. New York Wiley Sons. Creagh D.C. Bradley D.A. (2000). Radiation in art and archaeology. Amsterdam Elsevier. Dorrell P.G. (1994). Photography in archaeology and conservation. Cambridge Cambridge University Press. Douglas J.G. Jett P. Winter J. (Eds.). (2009). Scientific research on the sculptural arts of Asia proceedings of the third Forbes Symposium at the Freer Gallery of Art. London Archetype. Fagg B. (1968 October). The Nok culture excavations at Taruga. The West African archaeological newsletter 10 27 30. Fagg B. (1990). Nok terracottas. London Ethnographica. Fagg B.E.B. and Fleming S.J. (1970). Thermoluminscent dating of a terracotta of the Nok culture Nigeria. Archaeometry 12 pt. 1 53 55. Farr S. (2003 January 26). Test to determine age in ceramics is not foolproof – or scamproof. The Seattle Times. Fleming S.J. (1976). Authenticity in art. New York Crane. Fleming S. (1979). Thermoluminescence techniques in archaeology. Oxford Oxford University Press. Ghysels M. (2003 Winter). CT scans in art work appraisal. Art Tribal 04 116 131. Copyright 2009 Mark Rasmussen Rare Collections Page 30 of 30 All Rights Reserved Gibson L.H. (1978). Photography by infrared. Canada John Wiley Sons. Goksu H. Oberhofer M. and Regulla D. (Eds.). (1991). Scientific dating methods. Dordrecht The Netherlands Kluwer Academic. Haustein M. Krbetschek M.R. Pernicka E. (2003). Influence of radiation used by the security control at airports on the TL signal of quartz. Ancient TL 21(1). Jemkur J.F. (1986). Recent results of thermoluminescent (TL) tests on Nok terracottas and sherds. West African Journal of archaeology 16 165 168. Jemkur J.F. (1992). Aspects of the Nok culture. Zaria Ahmuda Bello University Press. Jett P. Douglas J.G. McCarthy B. Winter J. (Eds.). (2003). Scientific research in the field of Asian Art proceedings of the first Forbes Symposium at the Freer Gallery of Art. London Archetype. Jones M. (Ed.) (1990). The art of deception. California University of California Press. Ketcham R.A. Carlson W.D. (2001). Acquisition optimization and interpretation of X ray computed tomographic imagery applications to the geo sciences. Computers Geosciences 27 381 400. Lang J. Middleton A. (2005). Radiography of cultural material. 2nd ed. Amsterdam Elsevier. MacDonald L. (Ed.). (2006). Digital heritage. Germany Elsevier. MacLeod W.N. Turner D.C. Wright E.P. (1971). The geology of the Jos Plateau. Geological Survey of Nigeria bulletin 32 Volume 1 general geology. Martini M. Milazzo M. Piacentini M. (Eds.). (2004). Physics Methods in Archaeometry Proceedings of the International School of Physics Enrico Fermi . Amsterdam IOS. Mees F. Swennen R. Van Geet M. Jacobs P. (Eds.). (2003). Applications of X ray computed tomography in the geosciences. London Geological Society. Munshi P. (Ed.). (2009). Computerized tomography for scientists and engineers. New Dehli Anamaya. Ray S.F. (1999). Scientific photography and applied imaging. Oxford Focal. Rice P.M. (1987). Pottery analysis a sourcebook. Chicago University of Chicago Press. Salimbeni R. Pezzati L. (Eds.). (2005). Optical methods for art and archaeology. Bellingham WA SPIE. Shaw T. (1968). Radiocarbon dating in Nigeria. Nigeria Ibadan University Press. Shaw T. (1981 February). The Nok sculptures of Nigeria. Scientific American 244(2) 154 166. Stuiver M. Kra R. (Eds.). (1986). High precision calibration of the radiocarbon time scale AD 1950 500 BC. Radiocarbon 28. Taylor R. Aitken M.J. (Eds.). (1997). Chronometric dating in archaeology. New York Plenum. Uda M. Demortier G. Nakai I. (Eds.). (2005). X rays for archeology. Dordrecht The Netherlands Springer. Velde B. Druc I.C. (1998). Archaeological ceramic materials origin and utilization. Berlin Springer Verlag. Wagner G.A. (1998). Age determination of young rocks and artifacts physical and chemical clocks in quaternary geology and archaeology. Berlin Springer Verlag. Mark Rasmussen is the owner of Rare Collections a company that specializes in authentication scientific investigation and research. URL www.rare-collections.com ct scans artwork