the scientific detection of fakes and forgeries

THE SCIENTIFIC DETECTION OF FAKES AND FORGERIES

by Paul T. Craddock

ARTICLE DE FOND ( THE SCIENTIFIC DETECTION ... )

Dr. P.T. Craddock <[email protected]>,Dept. of Scientific Research, The British Museum, LondonUK, WC1B 3DG

Fakes and forgeries are the inevitable consequences of thehigh prices paid for antiquities and scientific investigationhas an important but sometimes equivocal role in theirdetection. Many articles have been written on the subjectbut the best book to date on scientific authentication isStuart Fleming's Authenticity in Art[2] and the subject will be coveredin some detail in this author's forth-coming book 1.

It should be made clear at once thatthere are two very different typesof deceptive antiquity, the forgerywhere the entire object is a recentproduction, made to deceive andthe fake, where an artefact of someage has been deceptively changed,usually to increase its value. Thelatter tend to prompt more interest-ing, questions, not just is it old ornew, but rather trying to establishwhat has happened to the piece,when and why. For this the coop-eration of the archaeologist or arthistorian is essential.

Scientific authentication can be per-ceived as a series of conflicts, with differing degrees of reali-ty, some are real, others not. The subject can be viewed as acontest between the forger, intent on deceiving scientificmethodology, and as a conflict between the perceived differ-ing approaches of art history and science.

To address, and hopefully to dispel, the latter first, there is aperception, mainly amongst the art historians, that the scien-tific approach is somehow more objective than their stylisticapproach. This probably arises because the scientific datacan so often be presented in numerical form, seeming tohave a finality that can brook no dissention. In fact, ofcourse, the very figures themselves have limits of detection,precision and accuracy, which even when quoted in reportsto the art historian seem to be rarely understood. Perhapsthe scientist really does need to explain the limits of confi-dence of the data more carefully. However, it is not thenumbers themselves, but rather their interpretation that isall important, and here it comes down to judgements basedon experience and reference to previous examinations and /or comparison with known genuine pieces, which of course,is exactly the approach adopted by the art historian.

In practice the art historian and the scientist must worktogether. Science can offer a range of powerful investigativetechniques but they must be directed. For example, someyears ago the British Museum was offered a Medievalbronze aquamanile (a vessel for holding water that could be

poured to cleanse the hands ofguests at banquets) in the form of aunicorn. Apparently unicorn aqua-maniles are very rare, and thusexpensive, but horses are muchmore common, and this was reflect-ed in the asking price. The onlyway in which the creature on offerdiffered from a horse was the horn.That clearly was the region of inter-est as explained to us by the curator,thus it was no great surprise whenradiography of the head showed thehorn was an insertion and non-destructive X-ray fluorescence (XRF)analysis showed the horn was ofbrass, just copper and zinc, whereasthe rest of the beast was a mixedalloy, of copper with tin, lead andzinc. Furthermore, the patina wasgenuine over most of the creature,but in the vicinity of the horn it was

synthetic. Proof certain that the horn was an addition andthus the aquamanile as a unicorn was a fake. If, howeverthe piece had been handed to us with no advice we wouldvery likely have gone for an inconspicuous area such as theunderside of the hooves and concluded that the piece wasgenuine, as indeed 99% of it was, it was the crucial 1% towhich we had to be directed.

So often in authentication work the object under scrutiny isnot a forgery but a deceptively restored damaged piece or amundane piece that, like the unicorn, has been transformedinto the unique. The fake Tudor coffee pot (Plate 1), now inthe possession of the Goldsmith's Company in London pro-vides a suitably bizarre example. The forgers of English sil-ver seem to have an inordinate respect for the hallmarkspunched on the pieces, and the ability of the Antique PlateCommittee of the Goldsmiths Company to detect falsemarks, they have, after all, 700 years experience! Thus mostforged and faked English plate manages to incorporate agenuine hallmark. These were the letters, denoting that thepiece had been assayed, as well as the date, place of assay

... it shows the quagmire ofembittered controversy inwhich a physical scientist islikely to have to wade once heinvolves himself with materialof doubtful origin. Readershaving it in mind to involvethemselves in authenticitytesting take warning.(These are the rueful remarks of MartinAitken [1] , of the Oxford Laboratory forArchaeology and the History of Art, con-cerning the problematic ceramics fromGlozel in France)

LA PHYSIQUE AU CANADA, VOL. 59, NO. 5 septembre / octobre 2003 235

1. Craddock, P.T., The Scientific Examination of Copies, Fakes andForgeries, Heinemann Butterworth, Oxford, (forthcoming).

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Francine Ford

Note

This is an official electronic offprint of the article entitled "The Scientific Detection of Fakes and Forgeries" by Paul T. Craddock, published in Physics in Canada, Vol. 59 No. 5 (Sept/Oct 2003), pp. 235-242. Copyright 2003, CAP/ACP All rights reserved/ Tous drots de reproduction réservés. F.M. Ford Managing Editor, PiC

236 PHYSICS IN CANADA, VOL. 59, NO. 5 September / October 2003

FEATURE ARTICLE ( THE SCIENTIFIC DETECTION ... )

and the maker. In this instance it seems that thebody of a late Medieval chalice has been taken andnow forms the body of a coffee pot. The body hashallmarks for London for the early 16th century,approximately 150 years before the first coffeereached England. The anachronism here is obviousbut chemical analysis could have been applied.Through the Post Medieval period and beyond thegold content of silver steadily declined as more andmore efficient means of recovering it were intro-duced [3] and thus it could be expected that thebody of the chalice would contain more gold thanthe spout, unless that had also been made from apiece of 16th century silver. However, the highergold contents are not invariable, for example, muchof the silver coming into Europe from SouthAmerica from the mid 16th century intrinsicallycontains very little gold.

HAN VAN MEEGEREN AND START OFSCIENTIFIC FORGERYTo a degree there is a real conflict between faker and scien-tist, with the former trying to anticipate the techniques ofthe latter, and the latter trying to stay one jump ahead. Thestory here commences with fine art, where back in the earlypart of the 20th century, scientific techniques such as radi-ography and identification of pigments began to be system-atically applied to paintings for authentication purposes,sometimes at dedicated laboratories such as that establishedat the Fogg Museum, Harvard in 1928. This was accompa-nied by the first issue of Technical Studies in the Field of FineArts in 1932, and the publication of books such as Martin deWild's Scientific Examination of Pictures in 1929 [4]. Thuswhen Han van Meegeren commenced on his career of forg-ing the paintings of de Hoogh and Vermeer in the early1930s [5] he anticipated that it was likely that they would besubjected to scientific authentication. He first carried outcareful experimentation to produce a medium that wouldgive a surface that would pass the then rather ad hoc tests,but more specifically he was very careful to try and ensurethat the reused canvases on which he painted would be con-vincing not only in natural light but by X-rays as well. Healso selected and ground his own pigments very carefullyso that they would be appropriate for the 17th century and

pass analysis. In particu-lar he used natural ultra-marine for his blues, man-ufactured from the naturalblue semi precious stone,lapis lazuli, and it is sure-ly no coincidence that thefirst chapter of de Wild'sbook is devoted to bluepigments and their recog-nition. He obtained hisultramarine, at greatexpense from Winsor andNewton in London.When, belatedly, X-raydiffraction (XRD) testswere performed on thepigments on his paintings,it was found that theultramarine had beenadulterated with cobaltoxide blue which wasvery much cheaper, possi-bly a case of the cheatercheated!

In fact van Meegeren neednot have taken such painsto ensure that his forgedpaintings would escapescientific detection. Noone bothered to seriouslytest them until after vanMeegeren's arrest for col-laborating with the Nazis.His crime was allegedlyselling to ReichmarshallHermann Goering, Dutch

masterpieces, namely one of his forged Vermeers. The sci-entific examination was finally carried out [6] , not as antici-pated by van Meegeren, to convince the Dutch art establish-ment that the paintings were authentic, but rather to try andconvince the court that they were forgeries. As a finalirony, after van Meegeren's death in 1947 a very bitter dis-pute took place between Coremans and the art historianJean Decoen, the latter convinced that some of the paintingswere genuine, including the Supper at Emmaus [7] , whichwas van Meegeren's first serious forged Vermeer and overwhich he had been especially careful.

Some years later measurements of the 210 Pb isotope of thelead in the lead white of the paintings showed that the leadis likely to have been smelted long after Vermeer's death [8] .

Put very briefly, the galena, PbS, lead ore usually containssmall amounts of 238 U, the long term decay of which gener-ates 226 Ra, which in turn begets 210 Pb, which itself decaysrelatively quickly to 206 Pb. Thus in the ground an equilibri-um becomes established, between the various isotopes, buton smelting the ore the radium and lead part company, themajority of the radium goes with the slag, whilst the 210 Pbnaturally goes with the rest of the lead. Thus immediately

Fig. 1 Plot of the Age / Radioactivityshowing the return to equilibriumof 210Pb after smelting of the leadore, which will have removed mostof the 226Ra. It is assumed herethat the activity of the 210Pb imme-diately after smelting was x100 theactivity of the remaining 226Ra.(From Fleming 1975, p.46)

Plate 1 From Chalice to Coffee Pot. (Courtesy theGoldsmith's Company)

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ation of the Order of the Round Table, inaugurated by KingEdward III in 1344.

The table is constructed radially from 49 great oaken plankscut from a limited number of trees. Absolute dating of thefelling of the trees is impossible because all of the plankshave been stripped of their bark and the majority of the sap-wood. Radiocarbon dating suggested a range of dates forfelling the trees, with the latest being in the 14th century.Dendrochronology indicated a similar wide range of fellingdates but suggested the trees were likely to have been felledin the mid 13th century. The estimated felling dates for theplanks from one tree varied consistently by between 60 to 70years and according to Biddle (p.328) 'show no semblance ofagreement'.

It is sobering to reflect that the dates produced by either ofthe conflicting techniques in themselves would have beenregarded as conclusive.

DRAKE'S PLATE OF BRASS The plate was reported to have been found in Marin Countyin San Francisco Bay in 1936. It carries a crudely carvedinscription claiming the surrounding land for QueenElizabeth of England in the name of Francis Drake, anddated 1579. If genuine this would be the very plate thatDrake, in his book The World Encompassed, stated that he hadleft as a record of his visit during his epic voyage.

The plate was first scientifically examined shortly after itsdiscovery by Fink and Polushkin [10] who, on the basis ofthe metal thickness, patina and composition claimed it asgenuine. Forty years later, and on the same criteria, Micheland Asaro [11] and Hedges [12] suggested that it was mod-

ern. Fink and Polushkin meas-ured the thickness of the plateand found it to be fairly uni-form at 3.38 ± 0.08 mm but stillconsidered it to be hammered.Michel and Asaro believed it tobe rolled sheet and thus mod-ern. In fact this is maybe of nogreat significance as some early17th century pictures are paint-ed on rolled copper sheet [13] .The patina was described asbeing soft and 'probably organ-ic', but was not analysed fur-ther. The composition of themetal itself is more interesting,and illustrates the sort of judge-ments that have to be made inauthenticity studies. The zinccontent was estimated from themetallographic structure in 1938to lie between 34 and 39%, andHedges[12] determined the com-position by XRF analysis ondrillings from several locationson the plate and found that theaverage zinc content was 34.8 ±

after smelting there is far more 210 Pb than could be account-ed for by the surviving amount of radium in the lead. 210 Pbhas a relatively short half-life and thus after a couple of cen-turies equilibrium between the 210 Pb and the remainingradium will have been re-established (Fig. 1). Samplestaken by Keisch from the lead white of Van Meergeren'spaintings, including the Supper at Emmaus, which Decoenshad pronounced genuine, showed the 210 Pb to be far toohigh in relation to the 226 Ra content realistically to havebeen smelted in the 17th century.

This seems to have been the final proof that has convincedeveryone, but it is chastening to realise that there were post-17th century cobalt pigments in the paint that could havebeen detected in the 1930s and if radiographs had beentaken then their careful examination would have revealedthat the paintings were made on canvases that were alreadyvery old when repainted. This would have provided damn-ing scientific evidence at the very outset if only anyone hadtaken scientific examination as seriously as van Meegeren.

In the author's experience there are perhaps more instancesof disagreements between the scientists themselves workingon the same object than between scientists and the art histo-rians. This can be either where different techniques werebeing used, as exemplified by the studies on King Arthur'sRound Table at Winchester, or sometimes even on the inter-pretation of the same data, as exemplified by Drake's Plateof Brass.

KING ARTHUR'S ROUND TABLE AT WINCHESTER This mighty table top is 18 feet in diameter, weighs 1.25tons, and has certainly been in the Great Hall at WinchesterCastle, in England since at least 1468 (Plate 2). Around theedges are emblazoned thenames of Arthur and hisknights and thus the table wasascribed by tradition to him.No one now seriously believesthat this was the Round Table,belonging to the ArthurianCamelot of legend, but ques-tions remained as to when thetable was made and why. Aspart of a major study of allaspects of the table, MartinBiddle [9] tried to resolve thesequestions, and unfortunatelyutilised two very differenttechniques, radiocarbon datingand dendrochronology, in abelt and braces approach thathe probably now deeplyregrets. Two possible occa-sions suggested themselves toBiddle, King Edward I held agreat tournament atWinchester in 1290, for whichthe table would have beenappropriate, or it could havebeen associated with the cre-

Plate 2 King Arthur's Round Table which has hung in theGreat Hall of Winchester castle for over 500 years.But which King had it made? Certainly not Arthur,but after one of the most intensive radiocarbonand dendrochronological surveys ever on a singleobject, we still don't know. (From CurrentArchaeology)

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0.4%, which represents good agreement between the twovery different methods of determination. The problemsarose over interpretation. Fink and Polushkin thought thatthe zinc content was acceptable for 16th century brass,Michel and Asaro and Hedges thought the zinc content toohigh for the brass to have been made by the cementationprocess, that was normally used in Post MedievalEurope [14] . In this process the calcined zinc ore, charcoaland finely divided copper were heated in a closed crucible.The charcoal reduced the zinc oxide to zinc vapour, some ofwhich dissolved in the copper to form the brass. Using thismethod the maximum zinc content was 33%, and the plateis apparently above that limit, but not by much. It was sug-gested that the brass must have been made by mixing cop-per and zinc metals together and was therefore modern.This is likely, but it must be stated that as early as 1512 car-goes of zinc metal were being imported into London fromIndia, presumably to be turned into brass [15,16] . Thusalthough it does appear that the plate is probably not of the16th century, the evidence is still far from conclusive.

APPROACHES TO AUTHENTICITY These can be covered here under three categories; the appli-cation of the standard archaeological physical dating tech-niques, radiocarbon, thermoluminesence (TL) and den-drochronology; technical examination to determine the com-position and methods of construction; and evidence of age-ing.

Dating

The advent of accelerator mass spectrometry (AMS) radio-carbon dating over the last 30 years, using samples meas-ured in milligrams, rather than the grams previouslyrequired, has made carbon dating a feasible method for dat-ing antiquities and art objects where minimal sampling is aprerequisite.

Probably the most well known AMS dating exercise to datehas been on the Shroud of Turin,where the 14 C content seemed toindicate that the flax from whichthe linen had been produced wasgrowing in the 13th or early 14thcentury AD, a date not farremoved from its first firmlyrecorded existence in France.Inevitably this was not the end ofthe debate, and for the often tor-tuous wranglings, sometimesbetween the scientists them-selves, see Wilson [17] andGove [18] . Many attempts havebeen made to explain away theradiocarbon date, including sug-gestions of all sorts of irradiationthat could have occurred at themoment of the Resurrection,thereby enhancing the 14 C con-tent. These scenarios have beendismissed by the dating scientistson the grounds that science only

deals with reproducible phenomena, rather forgetting thatthe Resurrection itself was most certainly a non-repro-ducible event, central to the beliefs of Christianity, whichmany of them profess to believe. Ultimately it comes downto faith, which, as yet, one cannot test with a spectrometer.

The calibration of radiocarbon dates has shown that there isnot a linear relationship between the 14 C content and time,there are certain periods in the past where there are signifi-cant deviations, making translation of radiocarbon yearsinto calendar years difficult. For most authenticity purposesthis is not so important where all that is being attempted isto distinguish between ancient and modern. One periodwhere the variations are significant, even for authenticitystudies, is the Post Medieval period. This means that formost items stylistically dated after about 1700 AD radio car-bon dating alone will not give a meaningful date, the piececould be original or recent.

One important exception to this is where the object incorpo-rates material the carbon of which formed part of organismsgrowing after 1950. These will contain greatly enhancedlevels of 14 C, known as "bomb carbon", originating fromatmospheric nuclear weapons testing [8] . This is very recog-nisable, and as the amount of 14 C in the atmosphere is nowslowly but steadily decreasing, following the test ban treatyof 1963, means that quite precise dates are possible in someinstances (Fig. 2). Even mushroom clouds can have a silverlining!

The Vinland Map

A recent example of how the presence of bomb carbon canbe used is given by the radiocarbon dating of the VinlandMap [19] . The story of the discovery of the map, its acquisi-tion and the continuing acrimonious debate over its authen-ticity has been set out by Skelton et al [20] and rather differ-ently by Seaver [21] , but can be summarised here. The map,bound in with a medieval manuscript, seems to have firstappeared in the late 1950s, although certain records of it

exist only from the early1960s. It is drawn in inkon parchment and depictsthe world, including in thetop left hand corner a largeisland to the west ofGreenland labelledVinland. The map pur-ports to date from the 15thcentury, and if genuine,would be the earliest carto-graphic depiction of NorthAmerica (It would also bethe first depiction ofGreenland as an island,and in the opposite righthand side of the map is aremarkably accurate depic-tion of north east Asia andthe islands of Japan).The scientific examinationhas previously concentrat-ed on the ink, and in par-

Fig. 2 Plot of the increase in the levels of 14C in the atmos-phere during the 1950s and 1960s, and as reflected inthe 14C of plants (from Ref. [8]).

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bronze. The two were analysed with an open architectureXRF set that allows quite large objects to be positioneddirectly in the beam of primary X rays (Plate 4). Thisshowed that the upper figurine in Plate 3 to be of brass, andthus it is not Etruscan but instead it is likely to have beencast in the 19th century by one of the Italian foundries thatspecialised in reproductions of antiquities. It should bestressed that these were quite legitimate copies and wereusually marked as such. However, stamps and other marksidentifying the piece as modern can all too easily be filled inor filed away, and the object offered for sale as an antiquity.

This case study must seem like the perfect illustration of thescientific approach swiftly providing a clear and unambigu-ous answer. But, of course, reality is different. All that hasbeen obtained is an identification of the metals at theuncleaned surface of the object. Surfaces may have beenplated, will almost certainly have corroded to some extent,and may well have been conserved. A salutary example isprovided by another Etruscan bronze. This is a large bowlthat was examined by the author as part of a general surveyof Etruscan bronzes [26] , and the XRF analysis of the surfaceshowed that it was apparently made of brass. The bowl isfrom of one of the most important groups of material fromancient Etruscan tombs in the British Museum. Thus theDept. of Greek and Roman antiquities received the newsthat one of the major components of the tomb contents waslikely to be a forgery with some alarm and readily consentedto a drilling being made into the body metal. Analysis of thedrillings showed the body metal to be of copper with sometin and lead, that is, a leaded bronze quite typical ofEtruscan bronzes. The zinc in the surface corrosion is likelyto have come from some unrecorded electrochemical treat-ment in the 19th or early 20th century to loosen and removesome of the corrosion [27] . In this treatment the bronzewould have been wrapped in zinc foil and placed in anaqueous acidic or alkaline electrolyte and sometimes a smallpotential was applied. The zinc dissolved releasing hydro-gen, which effected the reduction, and of course some of thezinc salts would soak into the remaining copper mineralisa-tion. Unless the bronzes were very carefully washed after-wards some zinc would remain. Thus many ancient bronzesprobably have zinc salts in their otherwise genuine patinas. The treatment of localised outbreaks of copper chloride cor-

ticular the presence of titanium dioxide in the form knownas anatase [22] . This was apparently only used in paints etc.from the 1920s, but others have claimed that the amountsdetected in the ink are orders of magnitude less than firstclaimed, and anyway anatase could have been produced atan earlier date.

The parchment itself has usually been regarded asmedieval, whatever the date of the map drawn upon it, andthe radiocarbon dates obtained by and Donahue et al [19] [see also Gove [23] ] were 15th century AD. It is usual prac-tice to carefully wash the samples before dating to removecontaminants, and Donahue et al [19] dated the extracts fromwashing with aqueous solutions of acid and alkali and withacetone. The extract dissolved by the aqueous treatmentwas found to contain bomb carbon. As nuclear testing onlygot underway in the early 1950s and the map in its presentform was seen by many people in the early 1960s, thisshows that the parchment must have undergone some seri-ous treatment in the 1950s just prior to its first appearance,as pointed out by Ambers and Bowman [24] . One can takethis further because although the organic components in thevarious extracts were not analysed, a common treatment forparchment is to size it with gelatine and the usual source ofthis would be animal bones or hides. These could well havepicked up bomb carbon and gelatine is, of course, water sol-uble. This new information would seem to disprove one ofthe leading hypotheses that the map was made in the 1930sto discredit the Nazis [21] , but it does show that somethingfairly major happened to the parchment on which the mapis drawn just prior to its appearance on the market.

MATERIALSAnother approach to authentication is to ascertain if theartefact is made of materials commensurate with its sup-posed age. With copper alloy items an important indicatoris whether the alloy is of bronze, the alloy of copper and tin,or of brass, the alloy of copper with zinc (NB antiquities orart objects made of copper alloy that are patinated arealmost invariably described as bronze no matter what theircomposition). Put very simply, brass began to be usedabout 2000 years ago over much of the Old World, thus anartefact of brass, which is stylistically much earlier will besuspect (for more on the history of zinc and brass, seeCraddock) [15] . For most authenticity studies non-destruc-tive methods are essential, and thus techniques such asenergy dispersive X ray fluorescence, once described as 'thecurator's dream instrument' are very useful [25] , and mod-ern portable sets make the technique very convenient. It ispossible to get a virtually instantaneous non-destructiveidentification of the inorganic components of an artefact, asthe following example shows.

The Two BanquetersThe British Museum possesses two 'bronze' figurines ele-gantly reclining at a banquet (Plate 3). One is clearly a copyof the other, but both are good castings, and have minimalcorrosion and are both generally in good condition, andthus it is not easy at a glance to tell which is original andwhich is the copy. They are Etruscan in style, dateable tothe early 5th century BC, that is, long before the generalintroduction of brass, the original really should be of

Plate 3 The two banqueters (T. Milton / The BritishMuseum)

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rosion with drops of silver nitrate is another potentialsource of misinterpretation, in danger of being mistaken forevidence of silver plating by the unwary analyst. Thoseengaged in authentication work must have a thoroughknowledge of the many processes and treatments that maybefall a real antiquity as well as those used by the fakers.

AGEINGThe characteristic surface changes that take place throughthe millennia, especially if the artefact is buried, provideanother approach to their authentication. There have beenmany studies on the patination of bronze, both natural andsynthetic, not least because as well as providing a means ofauthentication, the patina has always been the subject ofaesthetic appreciation in its own right [28,29] . Thus there isextensive information on the chemistry and mineralogy ofthe various naturally forming corrosion products on copperalloys and also on the characteristics of synthetic patina-tions, including those applied to deceive (see David Scott's2002 magisterial work on the subject) [13] .

The usual methods of examination include XRF with XRDand Raman microscopy to identify the minerals present.Where minerals have been stuck to the surface the organicbinders can sometimes be revealed by ultra violet radiation,which can induce fluorescence.

Problems can arise through the seemingly strange thingsthat can happen to antiquities, both real and forged. Forexample, in the 18th century there was a widely held viewthat classical bronzes originally had a black patina [28] .Unfortunately for the collectors, the bronzes coming out ofthe ground usually had a green patina. Some collectors,notably Richard Payne-Knight in England, were not abovegiving their bronzes the black patina they felt they ought tohave had. The Payne-Knight collection of some hundreds of

bronzes was purchased by the British Museum in the 1820s,and still forms a major part of the classical bronze collection.In the galleries where they are displayed their dark hues arevery noticeable compared to the bronzes alongside whichstill retain their natural patination.

The study on the surface alteration and patina on other met-als, notably stone, is much less advanced. This has beenillustrated by the authenticity studies over the past twentyyears or so, on the above life size marble statue of a youthin the Attic Greek style of the 6th century BC. This wasfinally acquired by the Getty Museum in 1986, but soonbecame their 'Curious Spurious Kouros' as acerbicallysummed up by Thomas Hoving [30] , the ex-director of theMetropolitan Museum of Art.

The statue was acquired from a supposed Swiss collection,which really did turn out to be spurious. Stylistic debateover the statue ranges those who believe it to be a master-piece of Classical antiquity against those who equally sin-cerely believe it to be a risible modern forgery [31] .

Thus scientific examination was called in to help, or as itturned out, to add to the confusion. Analysis of the stoneby a combination of techniques including petrology, miner-alogy, grain size analysis, trace element analysis, stable iso-tope analysis and cathodoluminescence identified the stoneas being dolomite most likely from the quarries on theisland of Thasos in the northern Aegean (see Herz 2001 foran overview article of the progress made in recent years onthe provenancing of marble in the Mediterraneanworld) [32] . The studies on the patination initially assumedthat it was largely formed of calcite, CaCO 3 , redeposited onthe surface of the marble following surface dissolution, in aprocess known as dedolomitisation, which is a well knownweathering phenomenon of dolomitic marbles duringburial [33] . However, subsequent XRD examination showedthe patina to be largely composed of Whewellite, hydratedcalcium oxalate. This has now been found on a number ofexposed marbles and is apparently related to the oxalatecoatings found on many rock surfaces, sometimes referredto as rock varnish etc., and seems to be formed from thedecomposition of the micro-organisms living on the rocksurface.

It was initially claimed that such oxalate deposits could notbe artificially induced, but latterly this was achieved byanother group of researchers by placing the marble in whatamounted to a vat of hot potato soup. The prevalence ofthese oxalate-based natural patinas on carbonate rocks hasonly very recently been fully appreciated, thus if the statuereally is a forgery, then someone back in the early 1980s atthe latest had given it a false patina of a type that was notgenerally known to exist. Attempts to date the rock varnishdirectly by AMS or cation dating have proved extremelycontroversial [34] .

INTERACTIONSThe serious forgeries of today are much more convincingthan previously because more is known of the ancient tech-nologies that would have been used to produce the genuinearticles. The adoption of the correct technology by the forg-ers generally dates from the extensive publication of the

Plate 4 One of the banqueters positioned in the path of theX-ray beam. Secondary X-rays emitted from the sur-face of the object are analysed and displayed on thescreen to the right. In this instance the two outerpeaks are for copper and the one in between is forzinc, suggesting that the figure is not a genuineEtruscan antiquity. (A. Milton / The BritishMuseum)

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well documented sites around the world where both lootingand faking was rife, exposure of the extent of the faking,often by scientific means, has had the effect of killing themarket and thereby saving the site from further depreda-tion. A good example is the ceramics from Haçilar, inTurkey.

Haçilar

Excavations conducted between 1957 and 1961 by JamesMellaart [36] at the small village of Haçilar, near to Burdur insouth west Turkey, uncovered remains of very sophisticatedceramic vessels and figurines dating from the 7th and 6thmillennia BC, arguably the earliest such figurines known.Mellaart's excavations were confined to the settlement whereinevitably the surviving fragments were in poor condition.Unfortunately there was no opportunity to locate the ceme-tery, which Mellaart suspected must exist, before the excava-tions came to an end.

Soon afterwards ceramics similar to those found on the exca-vation but in much better condition, began to appear on theinternational art markets, and over the next decade theywere acquired in considerable numbers by major museumsaround the world (Plate 6). But the greater range of shapesand the generally superior condition to those from con-trolled excavation began to arouse suspicions. Was itbecause they came from the putative cemetery, and beingburied intact were in better condition than those that hadbeen broken and trodden into the ground, or were they for-geries?The sheer quantity and sophistication of the unprovenancedmaterial on the markets was undermining all attempts tocategorize them, such was the uncertainty over their status.In order to clarify the situation a group of 68 pieces selectedfrom the collections of the British Museum in London, theAshmolean in Oxford, and the Metropolitan Museum inNew York were examined. The most significant test wasthermoluminescence dating which unequivocally showedthat a high percentage of them were recent productions [37] .After the publication of Aitken et al's report antiquities in theHaçilar style became unsaleable overnight.

technology concerned. Thus for example, the methods bywhich gold wires were produced in antiquity were firstinvestigated in the 1920s, but with little publication. Inantiquity gold and silver wires were usually made by eitherstrip or block twisting until about the mid first millenniumAD when the modern method of drawing thin rods throughthe holes in a draw plate was introduced and rapidlybecame universal (Plate 5). The forgers continued to usedrawn wires up until about the early 1970s when a consid-erable amount of research was carried out and widely pub-lished (Oddy 1977, for example) [35] . Since then all seriousforgers of ancient gold jewellery use strip or block twistedwire.

Many forgeries of oriental ceramics are so competent thatthere have been calls for technical information on the mate-rials and production methods to be omitted from reports.Such censorship of information may seem superficiallyattractive in the narrow world of dubious antiquities, but itis ultimately counterproductive and probably unworkableanyway. If this approach was followed through to its logi-cal conclusion then it should be extended to the stylistic ele-ments as well and the publication of the range of shapesand decorative motifs for a particular culture should also bebanned. The description and publication of all aspects ofthe material culture of the past has always been a core dutyof archaeology and curation, and it is not possible or desir-able to separate the technical from the stylistic aspects. Amore positive argument is that with the technical knowl-edge it is possible to easily detect many earlier forgeries,often made with consummate skill, but, as we now know,using the wrong materials and methods. The involvementof authenticity testing with material that has only veryrecently appeared on the market is a contentious subject,which must be addressed.

Another consequence of the rise in prices paid for antiqui-ties has been the quite ruinous despoliation of ancient sitesaround the world, looted for their saleable antiquities,which legislation has patently been unable to curb, muchless to stop. One of the few effective checks amongst collec-tors has been the fear of fakes and forgeries. On certain

a b c

Plate 5 Gold wire production ancient and modern: 4a) Strip twisting. A thin strip of gold is tightly twisted to form a tube withthe running helical edges visible. 4b) Block twisting. A thin rod of gold is twisted and rolled into a wire with theedges of the rod still surviving as helical grooves in the surface. 4c) Drawn wire: Where the gold has been drawnthrough a worn or damaged plate these distinctive parallel striations appear along the length of the wire. (A. Milton /The British Museum)

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It should perhaps also be noted that much simpler testswith drops of nitric acid on the surface had also been per-formed. These tests showed that the encrustation on theforgeries was not a genuine hard layer of calcite that haddeveloped on the surfaces over millennia, but was in factjust a layer of applied white clay. It does seem little short ofextraordinary that none of the major museums had appliedeven the simplest of tests prior to purchase. It is alsoextraordinary that so many leading museums acquiredmaterial that their curators believed to have been illegalexports, having been clandestinely dug up and therebydestroying valuable information on them and the culture towhich they belonged. As James Mellaart wrote in the intro-duction to his report [36] 'the whole affair was one of themost tragic chapters in the history of archaeology'.

The suspected presence of fakes amongst antiquities that,being illegal exports will have no firm provenance, has sha-ken confidence and thus depressed the market in antiquitieslooted from archaeological sites around the world. As withthe Haçilar ceramics, only scientific testing can establishwhether some classes of unprovenanced antiquity are gen-uine. Many of these are likely to have been looted and thereis clearly a duty on the part of responsible scientific institu-tions not to handle such material. The forging of antiquitieshas perhaps unwittingly achieved a real role in the preser-vation of the past that scientific testing must not jeopardise!

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London, (1985)..2. Fleming, S., Authenticity in Art, Institute of Physics, London,

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Plate 6 Forged or looted?: Ceramic figurines from Haçilar,the large double headed vase with obsidian inlaideyes is a forgery but legal. The small vessel on theright is authentic but looted (T. Heffron / BritishMuseum).

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the scientific detection of fakes and forgeries

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