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How to spot a fake
How to spot a fake
by Elen S. Humphreys
Think back to the last time you visited an art gallery or museum. As you wandered through the halls and peered at the various paintings and artifacts, did you ever question the information provided on the labels or in the guidebook? Did you wonder whether that Titian really is a Titian and not a fake? Did you question whether that vase had been correctly attributed to the Ming dynasty?
According to Richard Newman, head of scientific research at the Museum of Fine Arts, Boston, every museum contains artifacts that are not what they appear to be. “There are a lot of objects on display at the moment whose attributions are a little bit shaky,” he says. “There are some about which there are serious questions of authenticity and there are others we think are genuine but actually might be fakes.” Materials characterization techniques are central to identifying these fakes and to answering many other questions that the museum's curators may have about artifacts. The Museum of Fine Arts (MFA), Boston, has an enviable collection ranging from ancient Egyptian mummies to European paintings. Any one of its 400 000 artifacts could be the next project to come through the door of Newman’s laboratory. Often, curators just want to know more about an artifact to further their scholarly research. Or sometimes new information has given rise to a question about an object’s authenticity. A museum conservator may send an artifact to the lab because they want to find out more about its previous conservation or reconstruction so that they can decide how best to restore it. The objects arriving at the lab may be made from any material, range in size from the smallest coin to the largest Greek statue, and date from any time in history. Many of them are priceless and they are sometimes very fragile. The challenge facing Newman and his team is to answer the questions with non-destructive materials characterization or, if necessary, using only a tiny fragment of the artifact.
32
November 2002
ISSN:1369 7021 © Elsevier Science Ltd 2002
APPLICATIONS FEATURE
Fakes and copies We often think of forgeries as paintings, but in fact anything that is collectible and expensive is an attractive item to forge. For example, in recent years researchers at the MFA have tested numerous pieces of simple Neolithic Chinese pottery from the 3rd millennium BC, which have become popular with collectors and have been forged with some success. Often forgers will go to great lengths to reproduce the materials and processes, or the appearance, of the appropriate historical period. Not all incorrectly attributed items are intentional forgeries. In the same way that a museum shop might sell a print of a painting or a replica of a vase, copies of statues, paintings, and other precious artifacts have been popular through the ages. Some may be easy to spot, but others, perhaps even made in the same studio as the original, are much more difficult.
Where to start When planning an investigation, the museum scientist has to identify which properties of an artifact might yield clues to its origin. The starting point is always to find out as much of this information as possible using non-destructive techniques. Many familiar materials characterization techniques, in particular X-ray radiography, optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray fluorescence (ED-XRF), have proved their worth in the museum laboratory. The surface of an object often gives an indication of how it was made. A researcher can relate this information to when and where an artifact was made, because the technical processes available to various civilizations throughout history are well documented. Manufacturing processes leave telltale marks, such as casting where there may be some 'flash' or extra metal as a result of the molten material flowing into a small gap between molds, or turning by lathe, which leaves concentric lines, as does a pottery wheel. If sheet metal was the starting material, there may still be marks from the hammer that was used to beat it into shape. Some surface details are not visible to the naked eye, so an optical microscope or SEM may be used. The SEM is especially useful for observing small, metallic objects. For large objects, a copy of an area of interest on the surface can be made using a dental impression material. This gives a very good threedimensional reproduction of the surface, which can then be coated in a conducting material and imaged in the SEM.
Radiography has a long history of providing information from beneath the surface of museum artifacts. A sample from the object is bombarded with radiation (most commonly X- or beta-rays) to form a characteristic image of absorbing and non-absorbing regions. In a painting, for example, pigments that contain elements with high atomic weights, such as lead white and lead-tin yellow, absorb more X-rays and appear as light areas on the image. Other pigments and cracks do not absorb as many X-rays and appear dark. X-ray radiography can reveal hidden layers of paint, showing color and design changes made by the painter. A good example of this in the MFA’s collection is Rogier van der Weyden’s Saint Luke Drawing the Virgin (Fig. 1a). In galleries around the world there were four paintings purporting to be the original composition, painted around 1435-1440. There has been a long-running debate about which is the original and various techniques have been used to study the paintings. The combination of X-ray radiography with another non-destructive technique, infra-red reflectography (IRR), however, has provided valuable information. An IR reflectogram can reveal charcoal or graphite drawings from beneath the
Fig. 1 (a) ‘Saint Luke Drawing the Virgin’ by Rogier van der Weyden, dating from about 1435-40. Oil and tempera on panel. (Courtesy of the MFA, Boston.)
November 2002
33
APPLICATIONS FEATURE
Fig. 1 (b) X-ray radiograph of the Virgin’s head from ‘Saint Luke Drawing the Virgin’. The halo effect around the head and smudging of the left side of the face indicate that changes were made during the painting. (Courtesy of the MFA, Boston.)
paint layers because IR radiation is absorbed by carbon, but not by the constituents of paint. These complementary techniques reveal a wealth of information beneath the surface of the MFA painting. As Richard Newman explains, “There were many design and color changes made during the course of the painting, which you would only see in the original. He was obviously changing things as he went along.” One of the most notable changes is the shift in orientation of the Virgin’s head, which is revealed in both the X-ray radiograph (Fig. 1b) and the IR reflectogram (Fig. 1c). Other changes include the position of the Christ child, which was altered many times (Fig. 1d), Saint Luke’s position, which was moved up slightly, and an angel, who was drawn but never painted. Similar analyses of the other paintings revealed no design changes, leading to a wide acceptance that the painting at the MFA is the original. X-ray radiography is also widely used for analyzing threedimensional artifacts. An X-ray radiograph of a vase can show whether it has been restored or even put together from the fragments of several vases. This is a common type of forgery because a whole vase is far more valuable than the pieces. If beta-rays are used instead of X-rays, the watermarks on paper can be revealed. Watermarks are well documented, so
34
November 2002
Fig. 1 (c) IR reflectogram of the Virgin’s head from ‘Saint Luke Drawing the Virgin’, showing the underdrawing. The changes in position of the facial features indicate that the final position of the head varied from the original intended position. (Courtesy of the MFA, Boston.)
Fig. 1 (d) IR reflectogram of the Christ child from ‘Saint Luke Drawing the Virgin’, showing changes in the underdrawing of the Christ child and the Virgin’s hand. (Courtesy of the MFA, Boston.)
can lead directly to valuable information about the date and origin of a print, drawing, or document. If a non-destructive compositional analysis is needed, ED-XRF can provide information quickly without damaging
APPLICATIONS FEATURE
the artifact. It can even be used in situ when an object cannot be moved. X-rays bombard the sample, generating secondary radiations characteristic of the elements present, which are collected and analyzed. This technique can be used to detect most elements, but it is not very sensitive, for example to trace constituents. It is, however, particularly useful for analyzing corrosion-free metal objects made from simple alloys. It can also be a good starting point for further analyses, for example the pigments in different areas of a painting could be analyzed to determine from which regions to take samples for further analysis with more sensitive techniques.
Taking a hammer and chisel to a priceless artifact Often, more detailed analysis is needed and a small amount of material may have to be removed from an artifact. For a painting, the museum researchers usually take small samples from areas that are already damaged. They use a low powered optical microscope to select areas and an eye surgery scalpel for the operation. For the most comprehensive study of a painting, in which five or six different analytical techniques will be used, as many as two dozen samples may be taken. For ceramic, stone, and metal artifacts, the researchers use very small drills and saws, or sometimes even a hammer and chisel, to remove a small piece of material from the underneath or back of an object. Newman is untroubled by the thought of taking a hammer and chisel to a priceless sculpture. “We have some very valuable artifacts in the museum, especially paintings and sculptures,” he says, “but we’ve taken samples from lots of them.”
Age and authenticity Once it has been agreed that samples of material can be removed from an artifact, a whole new set of analysis tools becomes available to the museum researcher. One of the most obvious issues that can now be addressed is that of age. If an object is made from a natural, once-living material such as bone, wood, or fabric, then this question might be answered by radiocarbon dating. When a plant or animal dies it stops absorbing carbon, including the radioactive isotope 14C. The level of 14C is well known, as is the way in which it decays over time, so measuring the amount of 14C in a sample can tell us the date the living material died. The results must be interpreted with care, however, since the
material may pre-date the manufacture of the object. Radiocarbon dating has proven to be a useful technique in many cases, like the much-publicized analysis of the Turin shroud. Several laboratories dated the material to the 14th century, therefore revealing it as a fake. For artifacts made from other materials, less direct methods are used. Material composition can be a very reliable way of dating an object. Much is known about the materials that were available to different civilizations, so a good compositional analysis can tell researchers where and when an artifact was made. As well as ED-XRF, the analysis techniques used most frequently at the MFA are X-ray diffraction (XRD), IR spectroscopy, and chromatography. The technique or combination of techniques is chosen according to the material being analyzed, the information needed, and the sensitivity required. XRD, in which the characteristic angles of diffraction by the crystal lattice of a material are measured, is used to identify phases rather than elements. This makes the technique particularly useful for determining the composition of minerals, such as limestone and marble, where the mixture of phases can pinpoint exactly where the material came from. IR spectroscopy is used to identify both organic and inorganic materials. Spectra generated by the absorption of IR radiation by chemical bonds in a material can be compared with spectra from known reference materials. For organic materials, IR spectroscopy is often used in conjunction with either gas or liquid chromatography coupled with mass spectrometry (GC/MS or LC/MS) to give much more direct compositional information. In GC/MS, the vaporized sample is separated into its constituents, which are then identified by mass spectrometry. Materials that cannot be vaporized, such as some complex polymers and dyes of plant or animal origin, are analyzed using LC/MS. The MFA has a particularly large furniture collection and if a curator needs to know the ingredients of a furniture varnish, researchers would first use IR spectroscopy to find out whether the varnish is made of oil or resin or a mixture. Then chromatography could be used to find out more about the type of resin or oil, bearing in mind that it may have degraded since the time it was applied. Most commercial databases of materials do not take account of material degradation, so scientists at the MFA have built up their own databases, as well as referring to spectra in the literature.
November 2002
35
APPLICATIONS FEATURE
In addition to bulk materials, researchers can study the coating of corrosion, or patina, that builds up on a metal or stone artifact over time, often as a result of being buried or badly stored. Although there are ways for forgers to recreate a convincing-looking patina, it rarely stands up to chemical analysis. Even if the mix of minerals is correct, a binder is often used to make the patina adhere to the artifact, which can be easily identified. However, analysis of patina alone is never enough, because genuine artifacts with fake patinas do exist. The fashion among collectors has, over the years, swung between the desire for gleaming, clean surfaces and weather-beaten, ‘genuine’-looking surfaces.
Clues from the microstructure As mentioned above, the method used to manufacture an object can be revealed by its surface, but for more detailed information about the type of alloy, its mechanical and heat treatment history, and any joins in the material, observation of the material’s microstructure may be necessary. This is particularly useful for metallic artifacts, samples of which can be mounted in bakelite, polished, etched, and viewed in an optical microscope or SEM. Microstructural analysis can be combined with electron microprobe analysis, where the distribution of elements in the various microstructural components can be mapped.
After analysis, any remaining samples of artifacts are carefully archived in case the curators or researchers decide to reopen their enquiries at a later date. Some artifacts are the subject of intellectual debate for many decades. A case in point is the so-called Boston three-sided relief, a marble sculpture on display in the MFA, thought to be Greek in origin, dating from about 470-450 BC (Fig. 3). This has been scrutinized by art historians for almost a hundred years and by scientists for about fifty. Some art historians argue that there are stylistic reasons to believe that the relief is a fake, but there are very few similar objects for comparison. Recently, Newman and his team at MFA gathered together and added to the existing scientific evidence from gas chromatography, XRD, IR spectroscopy, and microstructural analysis, as well as other data. These data show that the marble is from the correct source and that the weathering
Piecing together the jigsaw New data about an artifact’s constituent materials and method of manufacture must be pieced together with other known information, such as where it was found and what else was found there. Then, collating this data with their own experience and information from the literature, researchers and curators can provide a recommendation regarding an object’s authenticity. Even then, the conclusion is not always clear-cut, as Richard Newman explains. “After a series of tests, there are some pieces that we feel are definitely authentic,” he says, “but others we’re not so sure. Every once in a while we prove that something is an out and out fake.” One inconclusive study carried out at the MFA was that of a small statue of a snake goddess (Fig. 2). Made from ivory and gold, the statue is thought to be either from the Minoan Bronze Age (1600-1500 BC) or else an early 20th century fake. In this case, because the hide glue and beeswax used in previous restorations have permeated the ivory, radiocarbon dating and other scientific analyses were not conclusive.
36
November 2002
Fig. 2 Statuette dating from the Late Minoan I, 1600-1500 BC, or early 20th century. Thought to be from Crete and made from ivory and gold. (Courtesy of the MFA, Boston.)
APPLICATIONS FEATURE
Fig. 3 Three-sided marble relief dating from the Greek Classical Period, about 470-440 BC. (Courtesy of the MFA, Boston.)
layers are appropriate, which provides a good case for the authenticity of the relief. Although the debate about style continues, the scientific evidence is strong enough that most scholars now believe it is authentic.
Going public All of this scientific investigation goes on behind the scenes at the MFA, and other museums like it. Museums and art galleries are arranged for visitors to enjoy the collection. Newman, however, believes that the public should be made aware when an object has questionable authenticity. “In past years, museums often didn’t like to advertise the problematic aspects of some of their objects on display,” he says. “In more recent years, we’ve been trying to change the labels on some of our problematic objects to reflect the question of authenticity.” The snake goddess, mentioned above, has just such a label.
So the next time you’re perusing a museum collection, remember that some of the labels may not be telling you the full story. The artifact you’re looking at might have been the subject of an intensive scientific study, employing half a dozen different characterization and analysis techniques to determine the date, composition, and method of manufacture. Large databases may have been trawled to find results from similar studies of comparable artifacts from around the world. The combined expertise of art historians, conservationists, materials scientists, and museum curators might have been pooled to come to the conclusion that the information on the label is overwhelmingly convincing. Or it might just be that this artifact has evaded attention and is a forgery waiting to be found out. MT
Acknowledgments The author would like to thank Richard Newman and Rhona MacBeth of the MFA, Boston, for their helpful discussions.
FURTHER INFORMATION AND READING 1. MFA, Boston, www.mfa.org 2. British Museum, London, www.thebritishmuseum.ac.uk 3. The Historical Metallurgy Society, www.hist-met.org 4. Reith, A., (1970) Archaeological Fakes, Barrie and Jenkins, London 5. Bowman, S., (ed.) (1991) Science and the Past, University of Toronto Press 6. Newman, R., and Herrmann Jr., J. J., Asmosia III Athens, (1995) p103-111 7. Lapatin, K. D. S., (2002) Mysteries of the Snake Goddess: Art, Desire and the Forging of History, Houghton Mifflin
8. Feller, R. L., et al., (eds.), (1986) Artists’ Pigments: A Handbook of Their History and Characteristics, Oxford University Press 9. Creagh, D. C., and Bradley, D.A., (eds.), (2000) Radiation in Art and Archeometry, Elsevier 10. Scott, D. A., (1991) Metallography and Microstructure of Ancient and Historic Metals, The Getty Conservation Institute in Association with Archetype Books 11. Purtle, C., (ed.) The Museum of Fine Arts, Boston, Rogier Van der Weyden St. Luke Drawing the Virgin: Selected Essays in Context, (1997) Brepols Publishers, Turnhout Belgium
November 2002
37
by Elen S. Humphreys
Think back to the last time you visited an art gallery or museum. As you wandered through the halls and peered at the various paintings and artifacts, did you ever question the information provided on the labels or in the guidebook? Did you wonder whether that Titian really is a Titian and not a fake? Did you question whether that vase had been correctly attributed to the Ming dynasty?
According to Richard Newman, head of scientific research at the Museum of Fine Arts, Boston, every museum contains artifacts that are not what they appear to be. “There are a lot of objects on display at the moment whose attributions are a little bit shaky,” he says. “There are some about which there are serious questions of authenticity and there are others we think are genuine but actually might be fakes.” Materials characterization techniques are central to identifying these fakes and to answering many other questions that the museum's curators may have about artifacts. The Museum of Fine Arts (MFA), Boston, has an enviable collection ranging from ancient Egyptian mummies to European paintings. Any one of its 400 000 artifacts could be the next project to come through the door of Newman’s laboratory. Often, curators just want to know more about an artifact to further their scholarly research. Or sometimes new information has given rise to a question about an object’s authenticity. A museum conservator may send an artifact to the lab because they want to find out more about its previous conservation or reconstruction so that they can decide how best to restore it. The objects arriving at the lab may be made from any material, range in size from the smallest coin to the largest Greek statue, and date from any time in history. Many of them are priceless and they are sometimes very fragile. The challenge facing Newman and his team is to answer the questions with non-destructive materials characterization or, if necessary, using only a tiny fragment of the artifact.
32
November 2002
ISSN:1369 7021 © Elsevier Science Ltd 2002
APPLICATIONS FEATURE
Fakes and copies We often think of forgeries as paintings, but in fact anything that is collectible and expensive is an attractive item to forge. For example, in recent years researchers at the MFA have tested numerous pieces of simple Neolithic Chinese pottery from the 3rd millennium BC, which have become popular with collectors and have been forged with some success. Often forgers will go to great lengths to reproduce the materials and processes, or the appearance, of the appropriate historical period. Not all incorrectly attributed items are intentional forgeries. In the same way that a museum shop might sell a print of a painting or a replica of a vase, copies of statues, paintings, and other precious artifacts have been popular through the ages. Some may be easy to spot, but others, perhaps even made in the same studio as the original, are much more difficult.
Where to start When planning an investigation, the museum scientist has to identify which properties of an artifact might yield clues to its origin. The starting point is always to find out as much of this information as possible using non-destructive techniques. Many familiar materials characterization techniques, in particular X-ray radiography, optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray fluorescence (ED-XRF), have proved their worth in the museum laboratory. The surface of an object often gives an indication of how it was made. A researcher can relate this information to when and where an artifact was made, because the technical processes available to various civilizations throughout history are well documented. Manufacturing processes leave telltale marks, such as casting where there may be some 'flash' or extra metal as a result of the molten material flowing into a small gap between molds, or turning by lathe, which leaves concentric lines, as does a pottery wheel. If sheet metal was the starting material, there may still be marks from the hammer that was used to beat it into shape. Some surface details are not visible to the naked eye, so an optical microscope or SEM may be used. The SEM is especially useful for observing small, metallic objects. For large objects, a copy of an area of interest on the surface can be made using a dental impression material. This gives a very good threedimensional reproduction of the surface, which can then be coated in a conducting material and imaged in the SEM.
Radiography has a long history of providing information from beneath the surface of museum artifacts. A sample from the object is bombarded with radiation (most commonly X- or beta-rays) to form a characteristic image of absorbing and non-absorbing regions. In a painting, for example, pigments that contain elements with high atomic weights, such as lead white and lead-tin yellow, absorb more X-rays and appear as light areas on the image. Other pigments and cracks do not absorb as many X-rays and appear dark. X-ray radiography can reveal hidden layers of paint, showing color and design changes made by the painter. A good example of this in the MFA’s collection is Rogier van der Weyden’s Saint Luke Drawing the Virgin (Fig. 1a). In galleries around the world there were four paintings purporting to be the original composition, painted around 1435-1440. There has been a long-running debate about which is the original and various techniques have been used to study the paintings. The combination of X-ray radiography with another non-destructive technique, infra-red reflectography (IRR), however, has provided valuable information. An IR reflectogram can reveal charcoal or graphite drawings from beneath the
Fig. 1 (a) ‘Saint Luke Drawing the Virgin’ by Rogier van der Weyden, dating from about 1435-40. Oil and tempera on panel. (Courtesy of the MFA, Boston.)
November 2002
33
APPLICATIONS FEATURE
Fig. 1 (b) X-ray radiograph of the Virgin’s head from ‘Saint Luke Drawing the Virgin’. The halo effect around the head and smudging of the left side of the face indicate that changes were made during the painting. (Courtesy of the MFA, Boston.)
paint layers because IR radiation is absorbed by carbon, but not by the constituents of paint. These complementary techniques reveal a wealth of information beneath the surface of the MFA painting. As Richard Newman explains, “There were many design and color changes made during the course of the painting, which you would only see in the original. He was obviously changing things as he went along.” One of the most notable changes is the shift in orientation of the Virgin’s head, which is revealed in both the X-ray radiograph (Fig. 1b) and the IR reflectogram (Fig. 1c). Other changes include the position of the Christ child, which was altered many times (Fig. 1d), Saint Luke’s position, which was moved up slightly, and an angel, who was drawn but never painted. Similar analyses of the other paintings revealed no design changes, leading to a wide acceptance that the painting at the MFA is the original. X-ray radiography is also widely used for analyzing threedimensional artifacts. An X-ray radiograph of a vase can show whether it has been restored or even put together from the fragments of several vases. This is a common type of forgery because a whole vase is far more valuable than the pieces. If beta-rays are used instead of X-rays, the watermarks on paper can be revealed. Watermarks are well documented, so
34
November 2002
Fig. 1 (c) IR reflectogram of the Virgin’s head from ‘Saint Luke Drawing the Virgin’, showing the underdrawing. The changes in position of the facial features indicate that the final position of the head varied from the original intended position. (Courtesy of the MFA, Boston.)
Fig. 1 (d) IR reflectogram of the Christ child from ‘Saint Luke Drawing the Virgin’, showing changes in the underdrawing of the Christ child and the Virgin’s hand. (Courtesy of the MFA, Boston.)
can lead directly to valuable information about the date and origin of a print, drawing, or document. If a non-destructive compositional analysis is needed, ED-XRF can provide information quickly without damaging
APPLICATIONS FEATURE
the artifact. It can even be used in situ when an object cannot be moved. X-rays bombard the sample, generating secondary radiations characteristic of the elements present, which are collected and analyzed. This technique can be used to detect most elements, but it is not very sensitive, for example to trace constituents. It is, however, particularly useful for analyzing corrosion-free metal objects made from simple alloys. It can also be a good starting point for further analyses, for example the pigments in different areas of a painting could be analyzed to determine from which regions to take samples for further analysis with more sensitive techniques.
Taking a hammer and chisel to a priceless artifact Often, more detailed analysis is needed and a small amount of material may have to be removed from an artifact. For a painting, the museum researchers usually take small samples from areas that are already damaged. They use a low powered optical microscope to select areas and an eye surgery scalpel for the operation. For the most comprehensive study of a painting, in which five or six different analytical techniques will be used, as many as two dozen samples may be taken. For ceramic, stone, and metal artifacts, the researchers use very small drills and saws, or sometimes even a hammer and chisel, to remove a small piece of material from the underneath or back of an object. Newman is untroubled by the thought of taking a hammer and chisel to a priceless sculpture. “We have some very valuable artifacts in the museum, especially paintings and sculptures,” he says, “but we’ve taken samples from lots of them.”
Age and authenticity Once it has been agreed that samples of material can be removed from an artifact, a whole new set of analysis tools becomes available to the museum researcher. One of the most obvious issues that can now be addressed is that of age. If an object is made from a natural, once-living material such as bone, wood, or fabric, then this question might be answered by radiocarbon dating. When a plant or animal dies it stops absorbing carbon, including the radioactive isotope 14C. The level of 14C is well known, as is the way in which it decays over time, so measuring the amount of 14C in a sample can tell us the date the living material died. The results must be interpreted with care, however, since the
material may pre-date the manufacture of the object. Radiocarbon dating has proven to be a useful technique in many cases, like the much-publicized analysis of the Turin shroud. Several laboratories dated the material to the 14th century, therefore revealing it as a fake. For artifacts made from other materials, less direct methods are used. Material composition can be a very reliable way of dating an object. Much is known about the materials that were available to different civilizations, so a good compositional analysis can tell researchers where and when an artifact was made. As well as ED-XRF, the analysis techniques used most frequently at the MFA are X-ray diffraction (XRD), IR spectroscopy, and chromatography. The technique or combination of techniques is chosen according to the material being analyzed, the information needed, and the sensitivity required. XRD, in which the characteristic angles of diffraction by the crystal lattice of a material are measured, is used to identify phases rather than elements. This makes the technique particularly useful for determining the composition of minerals, such as limestone and marble, where the mixture of phases can pinpoint exactly where the material came from. IR spectroscopy is used to identify both organic and inorganic materials. Spectra generated by the absorption of IR radiation by chemical bonds in a material can be compared with spectra from known reference materials. For organic materials, IR spectroscopy is often used in conjunction with either gas or liquid chromatography coupled with mass spectrometry (GC/MS or LC/MS) to give much more direct compositional information. In GC/MS, the vaporized sample is separated into its constituents, which are then identified by mass spectrometry. Materials that cannot be vaporized, such as some complex polymers and dyes of plant or animal origin, are analyzed using LC/MS. The MFA has a particularly large furniture collection and if a curator needs to know the ingredients of a furniture varnish, researchers would first use IR spectroscopy to find out whether the varnish is made of oil or resin or a mixture. Then chromatography could be used to find out more about the type of resin or oil, bearing in mind that it may have degraded since the time it was applied. Most commercial databases of materials do not take account of material degradation, so scientists at the MFA have built up their own databases, as well as referring to spectra in the literature.
November 2002
35
APPLICATIONS FEATURE
In addition to bulk materials, researchers can study the coating of corrosion, or patina, that builds up on a metal or stone artifact over time, often as a result of being buried or badly stored. Although there are ways for forgers to recreate a convincing-looking patina, it rarely stands up to chemical analysis. Even if the mix of minerals is correct, a binder is often used to make the patina adhere to the artifact, which can be easily identified. However, analysis of patina alone is never enough, because genuine artifacts with fake patinas do exist. The fashion among collectors has, over the years, swung between the desire for gleaming, clean surfaces and weather-beaten, ‘genuine’-looking surfaces.
Clues from the microstructure As mentioned above, the method used to manufacture an object can be revealed by its surface, but for more detailed information about the type of alloy, its mechanical and heat treatment history, and any joins in the material, observation of the material’s microstructure may be necessary. This is particularly useful for metallic artifacts, samples of which can be mounted in bakelite, polished, etched, and viewed in an optical microscope or SEM. Microstructural analysis can be combined with electron microprobe analysis, where the distribution of elements in the various microstructural components can be mapped.
After analysis, any remaining samples of artifacts are carefully archived in case the curators or researchers decide to reopen their enquiries at a later date. Some artifacts are the subject of intellectual debate for many decades. A case in point is the so-called Boston three-sided relief, a marble sculpture on display in the MFA, thought to be Greek in origin, dating from about 470-450 BC (Fig. 3). This has been scrutinized by art historians for almost a hundred years and by scientists for about fifty. Some art historians argue that there are stylistic reasons to believe that the relief is a fake, but there are very few similar objects for comparison. Recently, Newman and his team at MFA gathered together and added to the existing scientific evidence from gas chromatography, XRD, IR spectroscopy, and microstructural analysis, as well as other data. These data show that the marble is from the correct source and that the weathering
Piecing together the jigsaw New data about an artifact’s constituent materials and method of manufacture must be pieced together with other known information, such as where it was found and what else was found there. Then, collating this data with their own experience and information from the literature, researchers and curators can provide a recommendation regarding an object’s authenticity. Even then, the conclusion is not always clear-cut, as Richard Newman explains. “After a series of tests, there are some pieces that we feel are definitely authentic,” he says, “but others we’re not so sure. Every once in a while we prove that something is an out and out fake.” One inconclusive study carried out at the MFA was that of a small statue of a snake goddess (Fig. 2). Made from ivory and gold, the statue is thought to be either from the Minoan Bronze Age (1600-1500 BC) or else an early 20th century fake. In this case, because the hide glue and beeswax used in previous restorations have permeated the ivory, radiocarbon dating and other scientific analyses were not conclusive.
36
November 2002
Fig. 2 Statuette dating from the Late Minoan I, 1600-1500 BC, or early 20th century. Thought to be from Crete and made from ivory and gold. (Courtesy of the MFA, Boston.)
APPLICATIONS FEATURE
Fig. 3 Three-sided marble relief dating from the Greek Classical Period, about 470-440 BC. (Courtesy of the MFA, Boston.)
layers are appropriate, which provides a good case for the authenticity of the relief. Although the debate about style continues, the scientific evidence is strong enough that most scholars now believe it is authentic.
Going public All of this scientific investigation goes on behind the scenes at the MFA, and other museums like it. Museums and art galleries are arranged for visitors to enjoy the collection. Newman, however, believes that the public should be made aware when an object has questionable authenticity. “In past years, museums often didn’t like to advertise the problematic aspects of some of their objects on display,” he says. “In more recent years, we’ve been trying to change the labels on some of our problematic objects to reflect the question of authenticity.” The snake goddess, mentioned above, has just such a label.
So the next time you’re perusing a museum collection, remember that some of the labels may not be telling you the full story. The artifact you’re looking at might have been the subject of an intensive scientific study, employing half a dozen different characterization and analysis techniques to determine the date, composition, and method of manufacture. Large databases may have been trawled to find results from similar studies of comparable artifacts from around the world. The combined expertise of art historians, conservationists, materials scientists, and museum curators might have been pooled to come to the conclusion that the information on the label is overwhelmingly convincing. Or it might just be that this artifact has evaded attention and is a forgery waiting to be found out. MT
Acknowledgments The author would like to thank Richard Newman and Rhona MacBeth of the MFA, Boston, for their helpful discussions.
FURTHER INFORMATION AND READING 1. MFA, Boston, www.mfa.org 2. British Museum, London, www.thebritishmuseum.ac.uk 3. The Historical Metallurgy Society, www.hist-met.org 4. Reith, A., (1970) Archaeological Fakes, Barrie and Jenkins, London 5. Bowman, S., (ed.) (1991) Science and the Past, University of Toronto Press 6. Newman, R., and Herrmann Jr., J. J., Asmosia III Athens, (1995) p103-111 7. Lapatin, K. D. S., (2002) Mysteries of the Snake Goddess: Art, Desire and the Forging of History, Houghton Mifflin
8. Feller, R. L., et al., (eds.), (1986) Artists’ Pigments: A Handbook of Their History and Characteristics, Oxford University Press 9. Creagh, D. C., and Bradley, D.A., (eds.), (2000) Radiation in Art and Archeometry, Elsevier 10. Scott, D. A., (1991) Metallography and Microstructure of Ancient and Historic Metals, The Getty Conservation Institute in Association with Archetype Books 11. Purtle, C., (ed.) The Museum of Fine Arts, Boston, Rogier Van der Weyden St. Luke Drawing the Virgin: Selected Essays in Context, (1997) Brepols Publishers, Turnhout Belgium
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