by Mark Rasmussen, Stillwater, Minnesota and Thomas Amble, St. Paul, Minnesota
The purpose of this article is to present an overview of some of the advanced scientific techniques that are currently being used to evaluate artifacts. In addition, a number of traditional techniques are revisited and discussed within the greater framework of the Authentication Process. We would like to begin by thanking Tommy Beutell who was kind enough to loan us a few of his artifacts by Mark Rasmussen, Stillwater, Minnesota and Thomas Amble, St. Paul, Minnesota to demonstrate some of the techniques and provide a basis for discussion in this article.
The artifact collecting community has routinely used techniques such as microscopic analysis and ultra-violet inspection in the evaluation of artifacts, but the use of advanced imaging technology, scientific dating methods, and materials characterization techniques have rarely been used. Most collectors have had to rely on personal experience and the use of basic techniques to evaluate their artifacts. This separation between the analysis methods routinely utilized by members of the art and archaeological community and those of the artifact collector will eventually disappear as the importance and value of Native American material is fully recognized. As in many areas of collecting, it has been the use of formal analysis techniques, solid historical research, and scientific testing that has elevated objects to their current levels of importance and value. In addition, as the artifact collector and the archaeologist begin to share more methods and disciplines, the collaboration between the two communities can continue to mature.
The Authentication Process
The following is a description of the Authentication Process that serves as the standard framework that we apply when evaluating objects. All of the evaluation techniques presented later in this article are a small part of this larger process.
The process of authentication involves a wide variety of steps that are intimately linked and completely interdependent. There are steps to evaluate the provenance of an object, steps to evaluate the paperwork that documents it, and steps to evaluate any prior conservation or analysis efforts; while other steps evaluate the object itself on the basis of artistic qualities, stylistic norms, techniques, and materials. Further steps include comparables research and the identification of applicable analysis techniques. Authoritative Sources must be identified and consulted. Research into the potential and frequency of forgeries within the relevant areas must be completed. All of this information will then be analyzed and will guide the scientific analysis process, which will further support or cast doubts on authenticity. It should be noted that scientific testing alone can rarely establish authenticity (although it is often useful in detecting fakes or alterations). Similarly, no single step in the Authentication Process is generally conclusive.
The first and most important step in evaluating the authenticity of an object begins with 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 to support the authentication and dating processes. This information should include the exact date, the location and circumstances of the object’s collection and the identity of the collector, supplemented by a complete history of the object as it has changed owners. 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 object’s 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.
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 is thoroughly documented and that the documentation accompanies the object through the chain of ownership. For example, certain restorative procedures and certain types of testing (e.g., computed tomography, radiography, etc.) may impact the ability to perform certain types of authentication and dating procedures. Certain 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.
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 such individuals must be carefully reviewed and should be able to withstand reasonable scrutiny; multiple experts in each area should generally be consulted.
Reference materials – Reference materials that support the analysis process need to be identified and reviewed. Scientific journals that are peer reviewed 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 cannot be definitively tied back to Authoritative Sources must be avoided. Typically a diligent review of available literature and its accompanying references or bibliographies will help identify appropriate resources.
Reference collections – Reference collections provide the basis for comparative studies and should be identified. These collections must contain well-documented, authentic and inauthentic (for comparative study) objects with solid provenance.
This process looks to 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 research must utilize the full complement of Authoritative Sources. This collective knowledge will help define what techniques should be employed and will become the basis for the evaluation and interpretation of results.
Applicable analysis techniques – Every object willpresent 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 can impact or limit future analysis need to be carefully considered before use. A potential issue is the lack of consent for adequate analysis or destructive testing (taking required samples, CT scanning, radiographs etc.—please note: the term “destructive” does not mean that the object is destroyed; it merely refers to anything that affects the object). 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 nor should ever be made.
Scientific analysis – Analysis 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), it 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. 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 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 arrived at must also be considered invalid. The final process in scientific analysis is working with Authoritative Sources to correctly interpret the results of the analysis/testing and accurately compare them to definitive sources and/or statistically relevant expected norms.
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 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.”
Photographic analysis should always be considered an essential element in the evaluation of objects. In addition to providing quantitative data, it serves as part of the permanent record of the object and its condition at a given point in time. Detailed photographs can also prove invaluable in the unfortunate event that they become the only record of a stolen or damaged object.
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.
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, detecting surface accretions/deposits as well as highlighting areas of wear, damage, or restoration. In addition, IR can often penetrate old varnish and other coatings to reveal masked details. Examples would include the ability to reveal hidden writing, differentiate inks, uncover erased, worn or overwritten material, and recover writing on grimy, blackened, aged or burned surfaces. Obscured collection markings and damaged labels are a common problem that can sometimes be addressed by this technique.
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 safety glasses should be employed.
Whether you have a flexible bore/endoscope or a high-quality macro lens on your camera, the internal features of objects should be examined thoroughly and documented.
Additional Scientific Methods
Although not covered in this article, the following scientific techniques are commonly used in the analysis of archaeological material and may be utilized in the Authentication Process:
- Computer/Software Based Analytical Techniques
- Electron Spin Resonance Dating
- Microscopy (Stereo, Scanning Election, etc.)
- Obsidian Hydration Dating
- Quartz Hydration Dating
- Radiocarbon Dating
- Spectroscopic Analysis (Visible/Near Infrared, Infrared [FTIR], LA-ICP-MS, Raman, etc.)
- Uranium Series Dating
Thermoluminescence (TL) Dating
TL dating is a scientific technique that is applicable to such materials as pottery (baked clay objects), porcelain, burnt stone, burnt flint, and volcanic products. The basic principal is that minerals (mainly quartz, feldspar, and zircon) “record the passage of time” through the cumulative effect of prolonged exposure to the weak flux of nuclear radiation emitted by radioactivity in the object itself and in the surrounding burial soil (there can also be a small contribution from cosmic radiation). This “clock” is reset to zero (if sufficiently heated) during the original firing process and is indicative of the years since firing. 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 dating. Making sure that the samples are representative of the object as a whole and that they are not contaminated is critical to the process. The Native American headpot featured on the following page has been restored. CT scanning was performed to establish the condition and composition of the various fragments. This critical step would allow this object to be sampled for TL testing with the assurance that the areas being sampled are representative of the object as a whole. Forgers are aware of TL testing and often place authentic fragments where they feel sample takers would be most likely to take samples. CT scanning combined with TL testing is considered the most thorough and accurate method for evaluating these objects.
Specific TL Testing Issues
Many supposedly ancient ceramic objects have been found to be fake pastiche objects constructed from ageappropriate/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 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” during the normal course of conservation (interpreting the intent and context is the real issue). Additionally, 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 customer to guess at the intent, context, and meaning. In some instances, the report will mention that this is normal/routine and may minimize the issue. Objects with this type of notation on the TL report always require further evaluation and testing. The next major challenge with pastiche objects is that age-appropriate/authentic materials are often strategically placed where the TL sample taker is most likely to take samples. There are many problems with sample-taking for TL, 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 in this way and although they are “real” in a general sense, the primary esthetic is not. 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, sometimes 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 taken 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 only be undertaken by a fully qualified Conservator and must be considered in light of other techniques such as cr. This creates a bit of a chickenbefore-the-egg problem in that CT can illustrate the exact condition and composition of the object and guide you in taking TL samples but 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 affect TL dating owing to the low levels of radiation used and the relatively low precision of TL. The minimal risk (to TL etc.) associated with this radiation exposure can be further mitigated by including an appropriate dosimeter badge with the object during the CT scan and 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).
- Many TL labs do not routinely screen samples using FTIR (Fourier Transform Infrared Spectroscopy) or other sophisticated screening methods to check for binders/adhesives—they typically must subcontract (at the client’s request) for this analysis and have additional charges and sampling requirements. Some “contaminants” may reveal themselves by their effects on the “glow curve”, but not all will. 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 is useful when residue is actually found, it is generally considered inadequate. In the event that binders/adhesives are detected, you still have the challenge of interpreting their presence/context.
TL dating cannot reveal if 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 is carving new eyes into a highly eroded face. Another example is carving decorative elements from age-appropriate/authentic material and affixing them to an 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 date correctly but are inauthentic/fake.
Further problems with TL include the frequency of invalid or altered TL lab reports. Although some alterations/issues are easy to detect, some require forensic document examination techniques to discover. It is advisable to secure a certified copy of the original TL report (with its original photograph) from the issuing lab. Verifying the photograph (in addition to the report) is an important element, as mismatching reports and photos 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 – you should never just rely on the fact that it is old.
All TL labs are not created equal. It is very important to work with a lab that has the right reputation and experience. 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. Oxford Authentication is a recognized leader in the field and is an excellent laboratory with a great reputation and stringent controls.
Techniques like CT scanning, a thorough examination by a qualified Conservator and appropriate scientific testing techniques 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, solid provenance, and the knowledge of an art historian and/or archaeologist can contribute to a more complete understanding of these objects.