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1 The Role of Chemists in Archaeological Archaeological Chemistry IV Downloaded from pubs.acs.org by 80.82.78.170 on 12/26/16. For personal use only.
Studies Ralph O. Allen Department of Chemistry, University of Virginia, Charlottesville, VA 22901
This chapter is an overview of the wide variety of archaeological studies conducted by chemists. From the earliest stone artifacts to the artistic manuscripts and textiles of the more recent past, the studies presented in this volume show the wide range of materials that have been studied by chemical techniques. The field keeps expanding as chemists help provide information valuable in the interpretation of archaeological sites and artifacts. Besides helping to detect fraudulent artifacts and artistic objects in museum collections, chemists have studied the physicochemical deterioration processes that destroy the monuments and objects of the past. Thus, the role of chemists is more than just discovery of the past; it includes investigation that may help preserve the artifacts for future generations to enjoy and study.
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i n the p h y s i c a l artifacts of the past. E v e n w i t h o u t r e c o r d e d histories, the partial r e c o r d of materials that have s u r v i v e d the ravages of t i m e p r o v i d e s us w i t h insight i n t o ancient t i m e s . T h e oldest s u r v i v i n g materials are h u m a n bones a n d the s i m p l e stone artifacts that are e v i d e n c e of ancient w o r k m a n s h i p . T h e stone (or lithic) tools can b e u s e d to describe early c u l t u r e . W h e t h e r w e study the r o u g h c h i p p e d - s t o n e i m p l e m e n t s of the P a l e o l i t h i c era or the finer m i c r o b l a d e tools of the N e o l i t h i c era, it is clear that early h u m a n s k n e w the m e c h a n i c a l properties of m a n y natural materials. It was not u n t i l m u c h later that the methods of c h e m i c a l transformation w e r e l e a r n e d . E v o l u t i o n of c u l t u r e can b e traced i n the gradual r e f i n e m e n t of the stone tools p r o d u c e d a n d the materials u s e d b y early h u m a n s . E v e n t u a l l y , objects 0065-2393/89/0220-0001$06.00/0 © 1989 A m e r i c a n C h e m i c a l S o c i e t y
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w e r e made of native metals l i k e c o p p e r a n d gold. W i t h t i m e , a n d p r e s u m a b l y t h r o u g h e x p e r i m e n t a t i o n , fire was u s e d to alter the p h y s i c a l characteristics a n d e v e n the c o m p o s i t i o n of c e r t a i n materials. T h u s , artifacts l i k e pottery, mortar, glass, a n d m e t a l alloys have c h e m i c a l compositions that reflect the c h e m i s t r y of the r a w natural materials u s e d , as w e l l as the changes i n t r o d u c e d b y n e w a n d e v o l v i n g technologies. Differences i n c h e m i c a l compositions usually p r o v i d e n e w i n f o r m a t i o n about artifacts. B y differentiating b e t w e e n the sources of the r a w materials u s e d to p r o d u c e objects, it is possible to infer c u l t u r a l contacts. F o r some artifacts, d e t a i l e d studies of compositional differences can also h e l p us u n d e r s t a n d p r o d u c t i o n methods. T h e remains of the h u m a n s themselves m a y also be a n a l y z e d to p r o v i d e useful information. T h e contributions that c h e m ists have m a d e i n the study of archaeological materials have gone far b e y o n d the s i m p l e c h e m i c a l analysis of the materials. T h i s v o l u m e gives b u t a s m a l l part of the great c o n t r i b u t i o n s that chemists have made t o w a r d the u n d e r standing of ancient materials a n d technologies. T h e use of careful c h e m i c a l analysis to enhance the u n d e r s t a n d i n g of p r e h i s t o r i c technologies is not n e w . Archaeological c h e m i s t r y was p i o n e e r e d b y m a n y of the earliest chemists, i n c l u d i n g the seventh p r e s i d e n t (1882) of the A m e r i c a n C h e m i c a l Society, J o h n W . M a l l e t . M a l l e t ' s doctoral dissertation at the U n i v e r s i t y of G o t t i n g e n was the first account of a c h e m i c a l investigation of p r e h i s t o r i c C e l t i c objects, i n c l u d i n g precious stones, glass beads, p i g m e n t s , bronzes, a n d g o l d ornaments. A l t h o u g h analysis of the objects was difficult b y today's standards, the results w e r e accurate e n o u g h to p r o v i d e n e w insights into these C e l t i c artifacts. F o r example, M a l l e t u s e d the c h e m i c a l compositions to define the sources of the r a w materials. O n the basis of his geological a n d c h e m i c a l k n o w l e d g e , M a l l e t c o n c l u d e d that d u r i n g the early C h r i s t i a n t i m e s , the C e l t s u s e d o n l y native gold (which t h e y graded b y color) a n d h a d not yet discovered the means of extracting s i l v e r from ores. Since these early endeavors, the analytical techniques have i m p r o v e d , a n d the p o t e n t i a l role of the c h e m i s t i n archaeological studies has increased. G r e a t e r sensitivity i n the analysis of atomic a n d m o l e c u l a r species has h e l p e d scientists differentiate b e t w e e n artifacts. I m p r o v e m e n t s i n selectivity for the m e a s u r e m e n t of m o l e c u l a r species have generated m o r e i n f o r m a t i o n about decorative objects a n d those organic materials that have s u r v i v e d . T h e a b i l i t y to measure isotopic compositions accurately has p r o v i d e d some of the most valuable information for archaeological studies. F o r example, the analysis of carbon-14 has r e v o l u t i o n i z e d the d a t i n g of archaeological sites. W i t h the i m p r o v e m e n t of methods a n d the r e s u l t i n g increases i n d e t a i l e d c h e m i c a l studies of archaeological materials, the p r o b l e m s of data management a n d i n t e r p r e t a t i o n have increased. F o r t u n a t e l y , the increased availability of c o m puters to manage data bases has e n h a n c e d the ability of the c h e m i s t a n d the archaeologist to d e a l w i t h a l l of the data that is p r o d u c e d .
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O n e of the goals of this book is to illustrate h o w chemists use t h e i r k n o w l e d g e a n d n e w techniques to p r o v i d e f u r t h e r i n f o r m a t i o n o n t h e artifacts of past cultures. A n o t h e r goal is to acquaint archaeologists w i t h c h e m i c a l techniques that m a y b e useful to t h e m i n t h e i r studies, a n d to h e l p t h e m appreciate some of the p r o b l e m s i n the i n t e r p r e t a t i o n of c h e m i c a l data. Archaeologists a n d chemists m u s t , for example, u n d e r s t a n d the role of p r o p e r s a m p l i n g i n a p p l y i n g c h e m i c a l methods to archaeological p r o b l e m s . A r chaeologists m u s t appreciate that, e v e n t h o u g h the c h e m i s t can measure v e r y l o w concentrations w i t h great p r e c i s i o n , the differences b e t w e e n s a m ples m a y not be significant. T h e chemist's k n o w l e d g e of the materials t h e m selves m u s t be u s e d to h e l p the archaeologist k n o w w h i c h variations are significant. A r c h a e o l o g i c a l c h e m i s t r y is a marriage b e t w e e n two d i s c i p l i n e s a n d requires o n g o i n g cooperation a n d interaction. A s a result of this i n t e r a c t i o n , o u r k n o w l e d g e of the past a n d of materials (both natural a n d synthetic) increases. M a n y of the chapters i n Archaeological Chemistry IV show h o w chemists a n d archaeologists can w o r k together a n d g r o w i n t h e i r u n d e r s t a n d i n g of each other's d i s c i p l i n e s .
Trace Elements in Lithic Artifacts G l i m p s e s of the past are r e v e a l e d b y the few artifacts that are f o u n d . C a r e is r e q u i r e d to obtain as m u c h information as possible from these artifacts. I n most cases, the context a n d e v e n orientation i n w h i c h the object is f o u n d w i l l h e l p i n the e v e n t u a l i n t e r p r e t a t i o n of an archaeological site. H o w e v e r , c h e m i c a l analysis of a l l artifacts is b o t h i m p r a c t i c a l a n d u n w a r r a n t e d . T h e decision o n w h e t h e r to study an artifact a n d what techniques to use s h o u l d be based u p o n an u n d e r s t a n d i n g of the m a t e r i a l from w h i c h the object is made. T h i s decision can b e i l l u s t r a t e d b y c o n s i d e r i n g stone artifacts. A l t h o u g h early p e o p l e m u s t have u s e d m a n y natural materials, those l i k e the reeds a n d w o o d have decayed, whereas the l i t h i c or stone objects have s u r v i v e d . M a n y of the extant objects w e r e made from fine-grained h a r d stone l i k e flint. P h y s i c a l examination of these stone tools suggests that the styles a n d types of tools d i d not vary m u c h over l o n g periods of t i m e a n d over large geographical areas. T h e geological sources for h i g h - q u a l i t y r a w materials w e r e w i d e l y d i s t r i b u t e d a n d p r o b a b l y d i d not r e q u i r e a s o p h i s t i cated barter or exchange system. C h e m i c a l methods can sometimes be u s e d to d i s t i n g u i s h b e t w e e n stone artifacts that are made w i t h v e r y similar materials. L i t h i c r a w materials w e r e chosen because of p r o p e r t i e s , such as hardness, that d e p e n d u p o n c r y s t a l l i n i t y a n d c h e m i c a l composition. G e o c h e m i c a l processes d e t e r m i n e b o t h the c h e m i c a l c o m p o s i t i o n a n d p h y s i c a l properties of the rock. I n m a n y cases, l i t h i c artifacts do not r e q u i r e c h e m i c a l analysis to show that t h e y are made from different materials. A s i m p l e visual examination is frequently sufficient.
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I n C h a p t e r 2, H a n c o c k , P a v l i s h , a n d S h e p p a r d give an example of a case i n w h i c h visual examination o f stone tools was not adequate to differentiate b e t w e e n l i t h i c artifacts that w e r e p r o d u c e d from rocks that w e r e v e r y different i n t h e i r origins. D u r i n g the M e s o l i t h i c a n d early N e o l i t h i c t i m e s , the inhabitants of w h a t is n o w P o r t u g a l u s e d a variety of materials. A l t h o u g h most of the stone tools w e r e classified b y the archaeologists as s e d i m e n t a r y cherts, H a n c o c k c o n c l u d e d that m a n y tools w e r e made of volcanic r h y o l i t e . T h e basis for H a n c o c k ' s differentiation b e t w e e n rocks of different geological o r i g i n was the analysis of the i m p u r i t i e s (trace elements) i n the silicar i c h rocks. T h e trace e l e m e n t concentrations i n a p a r t i c u l a r rock d e p e n d p r i m a r i l y u p o n the minerals that are present i n the rock. A l t h o u g h there are m a n y factors to consider, generally trace elements i n minerals are i o n i c species that substitute i n a silicate crystal lattice. T h e degree of substitution depends o n h o w m u c h of the i m p u r i t y is present a n d o n h o w w e l l it is m a t c h e d i n i o n i c size a n d charge to the major ions i n the m i n e r a l . T h e silica lattice (quartz) itself does not accommodate i m p u r i t i e s , as there are no major cation sites at w h i c h substitution can occur. T h u s , trace e l e m e n t c o n c e n t r a tions t e n d to be v e r y l o w i n silica-rich rocks l i k e quartz a n d chert. C h a p t e r 2 describes a n u m b e r of silica (quartz)-rich rocks, b u t suggests that some that look l i k e c h e r t w e r e of volcanic o r i g i n , a n d thus c o n t a i n e d larger amounts of feldspar. Because feldspars are aluminosilicate, the presence of feldspar i n the r h y o l i t e is apparent from the h i g h e r concentration of A l (along w i t h associated N a , K , and Ca) i n those artifacts made of r h y o l i t e . S o m e of the most successful provenance studies have b e e n for o b s i d i a n , the glass f o r m e d from the r a p i d solidification of volcanic lava. O b s i d i a n was available o n l y i n l i m i t e d areas of volcanic activity, b u t because it was a natural glass, it p r o v e d to be an excellent m a t e r i a l for m a k i n g the sharp tools (e.g., knives) that are often f o u n d h u n d r e d s of m i l e s away from k n o w n sources of obsidian. M a t c h i n g an artifact to a distant obsidian deposit was possible because the c h e m i c a l compositions of these natural glasses are often q u i t e different. T h e c o m p o s i t i o n of volcanic lavas depends o n h o w m u c h rock has already c r y s t a l l i z e d from the lava. Because the trace elements are r e m o v e d from the lava b y s u b s t i t u t i n g for major elements i n a crystal lattice, the c o m p o s i t i o n of the lava a n d the r e s u l t i n g glass also depends u p o n the degree of crystallization (or l i k e w i s e partial m e l t i n g of rocks). T h e glass from a single lava flow is fairly homogeneous; therefore, s a m p l i n g is not as great a p r o b l e m as it is i n the case of a rock that is a m i x t u r e of several different m i n e r a l s . O f the m a n y studies of o b s i d i a n , B l a c k m a n ' s study of obsidian artifacts i n Iran f r o m the p e r i o d o f 3 5 0 0 to 1800 B . C . is t y p i c a l (I). T h e results s h o w e d that o b s i d i a n f r o m a single r e g i o n v a r i e d i n c o m p o s i t i o n because volcanic glass was p r o d u c e d at several different times throughout geological history. T h u s , the g r o u p i n g of artifacts b y u s i n g a hierarchical aggregative c l u s t e r i n g methodology d i d not necessarily identify distinct geographical sources.
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A s useful as the c h e m i c a l analysis of certain l i t h i c artifacts has b e e n i n e l u c i d a t i n g patterns of resource p r o c u r e m e n t , care m u s t always b e taken i n i n t e r p r e t i n g the results. F o r example, i n the early w o r k o n soapstone (steatite) artifacts, it appeared that the rare earth elements ( R E E ) w e r e p a r t i c ularly useful as " f i n g e r p r i n t s " for the geological sources (2). Soapstone was a w i d e l y u s e d soft rock, but it is a relatively rare geological m a t e r i a l f o r m e d b y local or regional m e t a m o r p h i s m . A n a l y s i s of m a t e r i a l from p r e h i s t o r i c quarries has s h o w n the variability i n the c o m p o s i t i o n of the soapstone from a particular outcrop. I n m a n y cases, the differences b e t w e e n source outcrops is greater than the variability w i t h i n a geological body. I n cases of regional m e t a m o r p h i s m w h e r e the geological formation is v e r y large, o n l y small a n d gradual c o m p o s i t i o n a l differences w e r e f o u n d i n outcrops that w e r e h u n d r e d s of miles apart (3). T h e use of trace elements to d e t e r m i n e patterns of resource use is not as h e l p f u l as w h e n d i s t i n c t outcrops have b e e n i d e n t i f i e d .
Analysis of Ceramic Pottery P o t t e r y is p r o d u c e d b y the conversion of s e d i m e n t a r y clay (produced b y the w e a t h e r i n g of rocks) into h a r d r o c k l i k e objects. T h e clay m i n e r a l s , w h i c h w e r e f o r m e d b y the c h e m i c a l d e c o m p o s i t i o n of certain r o c k - f o r m i n g m i n erals, contain trace elements. T h e sediments i n w h i c h these clays are f o u n d , h o w e v e r , also contain fragments of the p r i m a r y minerals f r o m the parent rock ( i n c l u d i n g grains of silica sand). These detrital components, w h i c h result from the p h y s i c a l a n d c h e m i c a l b r e a k d o w n of m i n e r a l s , are often a c c o m p a n i e d b y authigenic minerals that are c h e m i c a l l y p r e c i p i t a t e d from aqueous solutions. I n some ceramics, a d d i t i o n a l components w e r e a d d e d as t e m p e r during production. I f a clay s e d i m e n t c o n t a i n i n g a h i g h concentration of a u t h i g e n i c calcite ( C a C 0 ) was u s e d , the pottery p r o d u c e d was generally m o r e vitreous (glassy). W h e r e a s e d i m e n t c o n t a i n e d v e r y l o w amounts of C a , there w e r e technological advantages to a d d i n g C a as shell or calcite t e m p e r . I n C h a p t e r 3 b y A l l e n , H a m r o u s h , a n d Hoffman, the i m p o r t a n c e of C a i n the p r o d u c t i o n of P r e d y n a s t i c E g y p t i a n pottery is discussed. C h a p t e r 3 also describes some of the difficulties i n c h a r a c t e r i z i n g the r i v e r sediments that w e r e u s e d for pottery p r o d u c t i o n . S e d i m e n t s t e n d to be variable i n c o m p o s i t i o n a n d clay content because d u r i n g deposition from the r i v e r water there is sorting of grains according to size a n d density. E a r l y potters selected materials that w e r e r i c h i n clay, b u t i n some cases, t h e y separated coarser components f r o m the sediments. I n other cases, they a d d e d t e m p e r . I n C h a p t e r 4, B i s h o p a n d Neff discuss the effect of t e m p e r o n the c h e m i c a l analysis of pottery. T h e y p o i n t out that the c o n centration of an e l e m e n t m e a s u r e d i n a c e r a m i c artifact can be r e p r e s e n t e d mathematically. B i s h o p a n d Neff show that the analysis of pottery sherds 3
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alone can give rise to groups w i t h different compositions, because of the t e m p e r u s e d rather t h a n the source of the clay. Precise i n s t r u m e n t a l n e u t r o n activation analysis ( I N A A ) data was u s e d to show h o w v a r i a b i l i t y i n the c h e m i c a l c o m p o s i t i o n of ceramics can be accounted for b y the a d d i t i o n of volcanic ash. I n this case, the c l u s t e r i n g routines of the statistical analysis d i d not show differences i n the sources of the clays, b u t differences i n the p r o d u c t i o n methods. U n l e s s there are some geological a n d compositional differences b e t w e e n the clay sediments u s e d , the analysis of pottery w i l l not show different origins a n d c o u l d give m i s l e a d i n g results w h e n differences d u e to such things as t e m p e r occur. C h a p t e r 4 shows clearly h o w the speed a n d versatility of various statistical or pattern-recognition approaches to data analysis can outstrip the logic of the analysis. I n C h a p t e r 5, O l i n a n d B l a c k m a n explain that differences i n the c h e m i c a l compositions of pottery are caused b y b o t h the use of t e m p e r a n d b y c h e m i c a l a n d m i n e r a l o g i c a l differences i n the source of the clay. O l i n and B l a c k m a n report o n the c o n t i n u a t i o n of t h e i r studies of majolica (a c o m m o n earthenware pottery) f r o m the S p a n i s h C o l o n i a l p e r i o d i n M e x i c o . T h e y u s e d I N A A as w e l l as m i c r o s c o p i c examination of the m i n e r a l s to show that majolica p r o d u c e d i n S p a i n c o u l d b e d i s t i n g u i s h e d f r o m that p r o d u c e d i n M e x i c o . V o l canic t e m p e r was present i n the ceramics p r o d u c e d i n M e x i c o , a n d the c h e m i c a l analysis of these local ceramics suggested different p r o d u c t i o n c e n ters i n M e x i c o . T h e discovery of a c h e m i c a l l y distinct group of sherds a d d e d to the typological classifications of this pottery. M a n y times it is i m p o s s i b l e to identify a n d sample the sources of clay u s e d b y ancient artisans. I n these cases, c e r a m i c studies m u s t i n c l u d e a large n u m b e r of samples. I n C h a p t e r 6, H a n c o c k a n d F l e m i n g give an example of this k i n d of study. A large n u m b e r of samples of N e o l i t h i c Iranian c e r a m i c sherds (207 from three t i m e periods) w e r e analyzed as the first step i n d e t e r m i n i n g w h e t h e r there w e r e any r e a l compositional differences i n the pottery. T h e n o r m a l i z a t i o n approach d e s c r i b e d i n this chapter has a geological basis because minerals l i k e quartz (sand) can act a§ dilutants. N o r m a l i zation helps a v o i d m i s i n t e r p r e t a t i o n of the analytical results for ceramics. These authors also address some of the analytical p r o b l e m s , i n c l u d i n g c o n tamination a n d l e a c h i n g of the s h e r d w h e n it is b u r i e d . M a n y trace e l e m e n t studies of archaeological samples have used n e u t r o n activation analysis ( N A A ) . A l t h o u g h this t e c h n i q u e is not useful for a l l e l e ments, i t is v e r y sensitive for m a n y of those that have p r o v e d to be valuable indicators of geochemical processes (e.g., the rare earth elements). T h e p r e c i s i o n of the actual measurements is usually h i g h a n d easy to d e t e r m i n e . Samples can be i r r a d i a t e d w i t h little or no sample p r e p a r a t i o n , so there are few chances of c o n t a m i n a t i o n d u r i n g the analysis. H o w e v e r , the l i m i t e d n u m b e r of n u c l e a r reactors severely limits access to this type of analysis. W h e n samples are sent to a distant laboratory for analysis, the critical i n teraction b e t w e e n archaeologist a n d analyst can be lost.
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I n C h a p t e r 7, F o u s t , A m b l e r , a n d T u r n e r report o n studies of from the southwestern U n i t e d States u s i n g atomic absorption (AA) a n d i n d u c t i v e l y c o u p l e d p l a s m a ( I C P ) e m i s s i o n spectroscopy as alternatives to the m u c h m o r e expensive N A A . D i s s o l v i n g l i t h i c samples to prepare the solutions necessary for this type of analysis is a p r o b l e m , b u t n o w the methodology is m u c h m o r e r e a d i l y available to archaeologists. I n this study, t h r e e clays c o u l d be d i s t i n g u i s h e d o n the basis of the 8 elements they m e a s u r e d . A l t h o u g h m a n y of the samples c o u l d be assigned to a p a r t i c u l a r clay source, the analysis of the A n a s a z i pottery sherds gave results that w e r e somewhat ambiguous. T h e m i x i n g of clays or the a d d i t i o n of t e m p e r is d e s c r i b e d as the reason that h i g h levels of certain trace elements have b e e n f o u n d i n some of the sherds. F o r c e r a m i c studies w h e r e large n u m b e r s of samples m u s t be a n a l y z e d , the less expensive A A p r o c e d u r e may make c h e m i c a l analysis a m o r e r o u t i n e part of archaeological studies. O n e aspect of ancient c e r a m i c technology was the a d d i t i o n of various tempers to the clays. I n some cases, the a d d i t i o n of salts was u s e d to affect the colors a n d texture of the pottery (see C h a p t e r 3). I n C h a p t e r 8, M i t c h e l l a n d H a r t discuss a somewhat different approach to the study of c e r a m i c technology. T h e y l o o k e d at the m i n e r a l o g i c a l changes that clays u n d e r g o w h e n they are h e a t e d i n the presence of other minerals (especially those c o n t a i n i n g Ca). T h e m i n e r a l o g y , as d e t e r m i n e d b y u s i n g X - r a y diffraction, v a r i e d as a f u n c t i o n of t e m p e r a t u r e . A l t h o u g h such changes have the p o t e n t i a l to be u s e d to d e t e r m i n e firing temperatures, it is often necessary to c o n f i r m these temperatures b y other methods. N e v e r t h e l e s s , this research is an example of the basic studies i n ceramics a n d m i n e r a l o g y that have h e l p e d elucidate the e a r l i e r technologies.
Composition of Metal Artifacts and Art Objects T h e history of the use of various metals is p r e s e r v e d as a part of the a r chaeological r e c o r d . T h e age of a m e t a l artifact can be d e t e r m i n e d e i t h e r b y carbon-14 analysis of organic remains associated w i t h the artifact or b y its association w i t h ceramics of k n o w n age. I n m a n y cases, the technology u s e d for w o r k i n g the m e t a l or extracting it from ores can be o b t a i n e d from careful c h e m i c a l a n d microscopic analysis of the m e t a l artifact itself. M o s t of the metals that w e r e u s e d b y early p e o p l e are not v e r y abundant i n the earth's crust. F o r example, the average abundance of C u i n the crust is o n l y about 45 p p m . F o r t u n a t e l y , the processes of geochemical differentiation a n d m i n e r a l i z a t i o n t e n d e d to concentrate specific metals i n l o c a l i z e d deposits. T h e s e deposits w e r e often r e a d i l y recognizable b y t h e i r color a n d texture. W h e r e a s color may have b e e n i m p o r t a n t to the discovery of metals a n d ores, the t h e r m o d y n a m i c stability of the m e t a l c o m p o u n d s (the ease w i t h w h i c h the ores c o u l d be r e d u c e d to metals) d e t e r m i n e d the o r d e r i n w h i c h t h e y w e r e used. It is i n t e r e s t i n g that o n l y 8 of the 70 m e t a l l i c elements ( F e , C u ,
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A s , S n , A g , A u , P b , a n d H g ) w e r e r e c o g n i z e d a n d u s e d before the 18th century. T h e analysis of m e t a l artifacts has b e e n u s e d extensively to differentiate materials b y sources. X - r a y fluorescence a n d n e u t r o n activation analysis have b o t h p r o v e d valuable i n d e t e r m i n i n g e l e m e n t a l concentrations. N a t i v e m e t als, such as g o l d , c o n t a i n e d i m p u r i t i e s that c o u l d , i n some cases, b e u s e d to characterize t h e i r sources. H o w e v e r , the s m e l t i n g of ores to recover the metals often c h a n g e d the concentrations of i m p u r i t i e s . L a t e r , as alloys (e.g., b r o n z e a n d brass) w e r e p r o d u c e d , the compositions w e r e i n t e n t i o n a l l y a l t e r e d a n d c o n t r o l l e d . I n some cases, the re-use of materials or the lack of q u a l i t y c o n t r o l made the alloy c o m p o s i t i o n q u i t e variable (especially i n t e r m s of the trace components). A p r o m i s i n g approach to this p r o b l e m has b e e n the use of l e a d isotope ratios to characterize sources. C h a p t e r 9 b y G a l e a n d Stos-Gale is an example of this type of study. T h e isotopic ratios of l e a d are variable because some of the isotopes are the daughters f r o m the radioactive decay of u r a n i u m a n d t h o r i u m (4). E v e n t h o u g h the a m o u n t of l e a d i n b r o n z e artifacts is s m a l l , G a l e has b e e n able to d i s t i n g u i s h b e t w e e n sources of the ore o n the basis of the ratios of the various l e a d isotopes. T h e sources of silver, l e a d , a n d c o p p e r i n the B r o n z e A g e M e d i t e r r a n e a n are discussed. C h e m i c a l analysis, especially d e t a i l e d examination of inclusions w i t h scanning e l e c t r o n microscopy ( S E M ) , has p r o v i d e d considerable insight into m e t a l - w o r k i n g technology. C h a p t e r 10, b y M a n e a - K r i c h t e n , H e i d e b r e c h t , a n d M i l l e r is one example of a technological study. T h e i n t e r p r e t a t i o n of early s m e l t i n g practices is c o m p l i c a t e d b y the contamination from the cer a m i c c r u c i b l e s . T h i s c o n t a m i n a t i o n is i n d e e d a p r o b l e m as some of the fragments (from the archaeological site at T e l D a n , Israel) that this group investigated w e r e metal-fused to c e r a m i c crucibles. A l t h o u g h these results are p r e l i m i n a r y , the study does indicate some of the p r o b l e m s i n i n t e r p r e tation that can result w h e n the samples are not chosen to answer a specific question. T h e chapter i n c l u d e s a discussion of the sources for the t i n u s e d at this site. A l t h o u g h C h a p t e r 10 describes a study a i m e d at e l u c i d a t i n g early t e c h nological m e t h o d s , the research p r e s e n t e d i n C h a p t e r 11 b y C a r t e r a n d R a z i shows h o w the analysis of coins can p r o v i d e historical p o l i t i c a l i n f o r m a t i o n . T h i s chapter is the latest i n a series of c h e m i c a l studies of R o m a n coins that have b e e n i n c l u d e d i n the e a r l i e r v o l u m e s of the Archaeological Chemistry series. T h e s e studies have s h o w n h o w coins w e r e p r o d u c e d a n d h o w early R o m a n m i n t s functioned. C h a p t e r 11 shows h o w the p o l i t i c a l fortunes of the R o m a n E m p i r e affected the c o m p o s i t i o n of the coins. D e b a s e m e n t of the coins reflected periods of p o l i t i c a l t u r m o i l . C o i n s w e r e valuable as m o n e y , b u t they w e r e also artistic endeavors. M e t a l s have b e e n u s e d i n n u m e r o u s ways i n art objects. T h e great value of certain art objects has increased the n e e d for authentication, w h i c h is a
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different aspect of archaeological c h e m i s t r y . I n some cases, the process of authenticating art objects has p r o v i d e d chemists w i t h k n o w l e d g e about the artists' materials a n d techniques. C h a p t e r 12 b y W i l l i a m s , H o p k e , a n d M a g u i r e describes the X - r a y fluorescence analysis of m e d i e v a l L i m o g e s enamels. A l t h o u g h this is a p r e l i m i n a r y r e p o r t o n these g i l d e d c o p p e r ecclesiastical objects, the goal was to d e t e r m i n e the metals u s e d to create the different c o l o r e d enamels. X - r a y fluorescence was u s e d to analyze the different c o l o r e d e n a m e l regions. A l t h o u g h one goal of this research was to u n d e r s t a n d h o w the colors w e r e p r o d u c e d , c l e a r l y another aspect of this w o r k was to p r o v i d e a basis to d i s c r i m i n a t e b e t w e e n different materials of s i m i l a r appearance. A n o t h e r t y p e o f study that looks at the decorative, artistic objects o f the past is f o u n d i n C h a p t e r 13 b y D e m o r t i e r , E a r l y g o l d j e w e l r y was p r o d u c e d from p h y s i c a l l y w o r k i n g native metals. Intricate objects w e r e fashioned by brazing or soldering individual pieces together. D e m o r t i e r describes attempts to d e t e r m i n e h o w the b r a z i n g alloy u s e d i n ancient j e w e l r y was p r o d u c e d . D e m o r t i e r u s e d X - r a y s excited w i t h a b e a m of h i g h energy protons ( P I X I E ) to analyze m i c r o s c o p i c portions o f j e w e l r y t h o u g h t to b e o v e r 2000 years o l d . T h i s d e t a i l e d analysis r e v e a l e d four different k i n d s of b r a z i n g or s o l d e r i n g . A l t h o u g h several sources for this solder have b e e n suggested b y later descriptions i n the h i s t o r i c a l literature, D e m o r t i e r ' s a n a l ysis suggests that C d was used. T h e p o s s i b i l i t y of h a v i n g a C d - b a s e d solder i n antiquities from I r a n a n d S y r i a is discussed because it has b e e n a r g u e d that C d solders indicate m o d e r n forgeries. A n o t h e r example of d e t a i l e d m i c r o c h e m i c a l analysis is g i v e n i n C h a p t e r 14. O r n a , K a t o n , L a n g , M a t h e w s , a n d N e l s o n e x a m i n e d the c o l o r e d portions of several m e d i e v a l manuscripts b y u s i n g infrared microspectroscopy. I n one example, a forgery was d e t e c t e d o n the basis o f a b l u e i n k c o n t a i n i n g f e r r i c ferrocyanide that was not u s e d u n t i l 500 years after the m a n u s c r i p t was supposed to have b e e n p r o d u c e d . I n m a n y cases, this t y p e of e x a m i n a t i o n can h e l p authenticate a p a r t i c u l a r object a n d can a i d i n the d e v e l o p m e n t of greater u n d e r s t a n d i n g of the techniques u s e d b y the artists. I n some i n stances, inorganic salts w e r e u s e d to p r o d u c e c o l o r e d inks. T h e s e inks w e r e a n a l y z e d b y u s i n g X - r a y diffraction. F o r t i n y samples o f organic inks, a microscopic attachment to a F o u r i e r transform infrared spectrometer ( F T I R ) was valuable. B e s i d e s s h o w i n g w h i c h materials w e r e u s e d for s i z i n g a n d t a n n i n g the p a r c h m e n t s , F T I R h e l p e d O r n a et a l . identify the source of the r e d i n k as some species of insect. T h e i m p o r t a n c e o f p r e s e r v i n g archaeological m o n u m e n t s is discussed b y B u r n s a n d M a t s u i i n C h a p t e r 15. C h e m i c a l i n f o r m a t i o n not o n l y helps our u n d e r s t a n d i n g o f early technologies, b u t can h e l p answer questions about h o w best to p r e s e r v e a n object. B u r n s a n d M a t s u i describe t h e i r studies of v e r y large art objects: the r i c h l y decorated tombs of the E g y p t i a n pharaohs. D e t e r i o r a t i o n o f these m o n u m e n t s has r e s u l t e d f r o m p h y s i c o c h e m i c a l p r o c esses that are site-specific. D e t e r i o r a t i o n often depends o n such things as
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the c o m p o s i t i o n of the plaster or the rock f r o m w h i c h statues are c a r v e d . C h a p t e r 15 describes experiments u s i n g X - r a y photoelectron spectroscopy a n d e l e c t r o n m i c r o p r o b e analysis to d e t e r m i n e w h y the p a i n t e d murals o n the walls of tombs have d e t e r i o r a t e d so r a p i d l y . T h e goal of u n d e r s t a n d i n g the c o m p l e x m e c h a n i s m of deterioration (which involves the plaster, the p i g m e n t , a n d the atmosphere) is to devise conservation measures to protect a n d restoration practices to revitalize these ancient works of art.
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Proteinaceous and Organic Artifacts Besides the stone o r l i t h i c tools, bones represent another large class of artifacts that have s u r v i v e d because of t h e i r m i n e r a l o g i c a l nature. T h e p h y s ical characteristics of these bones have p r o v i d e d m u c h i n f o r m a t i o n about h u m a n e v o l u t i o n . T h e r e have b e e n extensive studies u s i n g l i g h t a n d e l e c t r o n microscopes to elucidate the structures of fossil shells, bones, a n d teeth. I n some of these studies, various fossil components seen w i t h the scanning e l e c t r o n microscope w e r e a n a l y z e d c h e m i c a l l y to ascertain w h e t h e r the s t r u c tures w e r e c o m p o s i t i o n a l l y related to t h e i r m o d e r n counterparts. T h e s e experiments r e v e a l e d d e t a i l e d m i c r o s c o p i c a n d compositional similarities. W i t h the advent of i m p r o v e d methodologies, it became clear that bones a n d similar m i n e r a l i z e d portions of l i v i n g organisms c o u l d preserve some o f the proteinaceous m a t e r i a l of the organism. A l t h o u g h proteinaceous m a t e r i a l d i d s u r v i v e , it was a l t e r e d over t i m e . S o m e studies have concentrated o n the assignment of t i m e scales to the archaeological r e c o r d o n the basis of the changes i n the p r o t e i n c o m p o s i t i o n of b o n e a n d t e e t h o v e r t i m e . O t h e r studies have a t t e m p t e d to d i s c e r n p a leopathological data a n d dietary i n f o r m a t i o n from the analysis of the calcified tissue. H o w e v e r , i n a l l cases, r e l a t i v e l y little is k n o w n c o n c e r n i n g the basic biological processes of p o s t b u r i a l change i n these proteinaceous materials. T h u s , the study of proteins i n archaeological materials continues to focus o n u n d e r s t a n d i n g h o w the p o s t b u r i a l e n v i r o n m e n t affects c h e m i c a l a n d p h y s i c a l changes i n the proteins themselves, as w e l l as a t t e m p t i n g to answer specific archaeological questions r e l a t i n g to diet, age, etc. A t the 8 t h S y m p o s i u m o n A r c h a e o l o g i c a l C h e m i s t r y i n D e n v e r , a n u m b e r of papers dealt w i t h the i m p o r t a n t research o n proteinaceous matter i n archaeological materials. T h e s e papers are b e i n g p u b l i s h e d elsewhere, b u t some of the research i n the field m u s t b e s u m m a r i z e d for the sake of completeness. I n the p i o n e e r i n g w o r k o n the occurrence a n d stability of proteins a n d a m i n o acids i n fossils, A b e l s o n d e t e r m i n e d that t h e r m a l l y unstable a m i n o acids such as t h r e o n i n e a n d serine w e r e e i t h e r m u c h r e d u c e d or absent i n fossils, whereas m o r e stable a m i n o acids, such as glycine a n d alanine, w e r e still present (see ref. 5). T h e total concentration of amino acids decreases dramatically w i t h t i m e , v o n E n d t and E r h a r d t r e p o r t e d t h e i r results c o n c e r n i n g the differential c h e m i c a l disintegration of a m i n o acids i n compact
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faunal bones from three archaeological sites (6). T h e y also r e p o r t e d o n t h e c o m p o s i t i o n a n d state o f preservation o f proteinaceous m a t e r i a l i n t h e c a l culus from p r e h i s t o r i c h u m a n teeth. T h e results o f a m i n o a c i d analysis o f similar bones from each site i n d i c a t e d that there was significant w i t h i n - s i t e variability, a n d that t h e most c h e m i c a l l y reactive amino acids v a r i e d t h e most. T h e stability o f b o n e decreases i n p r o p o r t i o n to d e p t h o f b u r i a l a n d i n r e l a t i o n to t h e severity o f the soil e n v i r o n m e n t . T h e a m i n o acid content of d e n t a l calculus differs greatly from that o f b o n e . A m i n o a c i d analysis o f calculus from three distinct A m e r i c a n I n d i a n populations differed b y m o r e than 1 0 % b e t w e e n groups. Isomeric forms o f a m i n o acids result from different arrangements o f the different atoms o r groups o f atoms a r o u n d a n a s y m m e t r i c carbon atom o r c h i r a l center. A l t h o u g h laboratory-produced a m i n o acids are usually a m i x ture o f the L a n d t h e e n a n t i o m e r i c D isomers, those p r o d u c e d i n biological systems are v i r t u a l l y a l l present i n t h e L configuration. Isoleucine has t w o c h i r a l centers a n d can thus exist as the D,L-isoleucine p a i r , o r as the closely related D,L-alloisoleucine p a i r . Rearrangement of atoms o n the c h i r a l carbons of t h e naturally o c c u r r i n g p r o t e i n a m i n o a c i d L-isoleucine results i n t h e formation of the n o n p r o t e i n a m i n o acid D-alloisoleucine. T h i s rearrangement process, c a l l e d e p i m e r i z a t i o n , must occur i n t h e proteinaceous m a t e r i a l o f fossils because alloisoleucine is observed (see ref. 7). I n d e e d , i n o l d e r fossils the a m o u n t o f isoleucine decreases a n d t h e amount o f alloisoleucine i n creases. A m i n o acids s u c h as alanine, aspartic a c i d , a n d isoleucine m a y change from L to D configurations over t i m e b y t h e process o f racemization. T h e s e changes found i n fossils l e d H a r e a n d A b e l s o n to suggest that e p i m e r i z a t i o n a n d racemization m i g h t b e u s e d i n techniques for dating s h e l l a n d other proteinaceous m a t e r i a l (8). H o w e v e r p r o m i s i n g these results appeared, i t soon became apparent that there w e r e complications i n a p p l y i n g this theory of a m i n o acid dating. F o r example, the half-life for t h e e p i m e r i z a t i o n o f isoleucine i n c o w b o n e was calculated to b e 110,000 years i n b o n e at 20 ° C and 290,000 years at 15 °C. T h i s finding shows h o w sensitive the reaction is to t e m p e r a t u r e , a factor that is often n o t k n o w n for archaeological s p e c i mens (9). S o m e p r o b l e m s c a n b e o v e r c o m e i f radiocarbon d a t i n g o f b o n e from the same site can b e used to " c a l i b r a t e " the racemization rates o f a m i n o acids. P r o b l e m s r e m a i n , a n d differing lines o f evidence suggest that r a c e m i zation d a t i n g o f b o n e i s , at best, tentative, a n d that m a n y o f the " e a r l y " dates for h u m a n skeletons are w r o n g . F o r instance, t h e S u n n y v a l e skeleton (racemization dated at 70,000 years B.P.) is morphologically i n d i s t i n g u i s h a b l e for skeletons dated b e t w e e n 400 a n d 1600 years B . P . (10). A n o t h e r i m p o r t a n t a n d controversial skeleton was d e s c r i b e d i n D e n v e r . B a d a a n d Masters p r e sented t h e results o f a d e t a i l e d study o f the general c o m p o s i t i o n a n d extent of racemization o f a m i n o acids isolated from the D e l M a r M a n skeleton (11).
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Archaeological Chemistry IV Downloaded from pubs.acs.org by 80.82.78.170 on 12/26/16. For personal use only.
T h e s e remains w e r e f o u n d e r o d i n g from the face of a coastal bluff i n D e l M a r , C A , i n 1929. A variety of dates have b e e n o b t a i n e d for these r e m a i n s , d e p e n d i n g u p o n w h i c h materials w e r e analyzed a n d w h i c h d a t i n g m e t h o d was u s e d . B a d a a n d M a s t e r s r e p o r t e d o n n e w dates based u p o n the n e w a n d m o r e sensitive C - 1 4 d a t i n g t e c h n i q u e . T h e results, o b t a i n e d o n a m i n o acids isolated f r o m the b o n e , i n d i c a t e d that the skeleton was 5400 years o l d . T h e s e results w e r e made possible b y the m o r e recent i m p o r t a n t advances i n carbon d a t i n g that are d e s c r i b e d i n C h a p t e r 16. I n C h a p t e r 16, H a r b o t t l e a n d H e i n o address the p a r t i c u l a r a p p l i c a t i o n of c a r b o n isotopic d a t i n g to textile fibers. T h e discussion of the accelerator mass s p e c t r o m e t r i c ( A M S ) t e c h n i q u e , w h i c h allows the accurate m e a s u r e ments o f isotopic ratios i n v e r y small amounts of carbon, shows w h y this t e c h n i q u e has h a d s u c h an i m p o r t a n t i m p a c t o n the field. C h a p t e r 16 s u m marizes the progress i n this v e r y i m p o r t a n t methodology that remains the most accurate absolute measure of the ages of artifacts. O t h e r isotopic measurements may also b e useful i n p r o v i d i n g i n f o r m a t i o n o n proteinaceous material. Because a m i n o acids contain n i t r o g e n , an analysis of the n i t r o g e n r e m a i n i n g i n p r e h i s t o r i c bones m a y p r o v i d e an a p proximate i n d i c a t i o n o f the q u a n t i t y of p r o t e i n r e m a i n i n g i n the bone. P e r haps o f greater i m p o r t a n c e , the n i t r o g e n that remains m a y also p r o v i d e insight into diet. I n the papers p r e s e n t e d i n D e n v e r b y H a r e , F o g e l , Stafford, a n d H o e r i n g (12), as w e l l as i n the paper b y B a d a a n d M a s t e r s (II), the isotopic analysis of carbon a n d n i t r o g e n w e r e d e s c r i b e d . H a r e n o t e d that most of the a m i n o acids i n collagen f r o m bones of animals that h a d b e e n r e a r e d o n c o n t r o l l e d diets w e r e e n r i c h e d i n C - 1 3 a n d N - 1 5 as c o m p a r e d to the c o r r e s p o n d i n g a m i n o acids i n t h e i r food. T h r e o n i n e was an e x c e p t i o n a n d was d e p l e t e d i n N - 1 5 relative to that i n the food source. U n l i k e most a m i n o acids, t h r e o n i n e does not d e r i v e its n i t r o g e n v i a transamination from the c e l l u l a r n i t r o g e n p o o l , b u t rather i n h e r i t s it from the t h r e o n i n e that is c o n s u m e d . T h e isotopic fractionation o f N - 1 5 i n t h r e o n i n e has b e e n s u g gested as a means to d i s t i n g u i s h b e t w e e n h e r b i v o r e s a n d carnivores at different levels i n food chains. T h e patterns o f stable isotope content i n a m i n o acids from bones o f fossil h e r b i v o r e s a n d carnivores w e r e r e p o r t e d to b e well-preserved. T h e r e can be little q u e s t i o n about the the value of absolute techniques for d e t e r m i n i n g the ages of artifacts. A s the ability to measure isotopic ratios has i m p r o v e d , not o n l y has the i m p a c t of carbon d a t i n g i m p r o v e d , b u t a n e w t e c h n i q u e has b e e n proposed. I n C h a p t e r 17, T a y l o r , Slota, H e n n i n g , K u t shiera, a n d P a u l discuss the feasibility of u s i n g a l o n g - l i v e d isotope of c a l c i u m (Ca-41) as a means o f d e t e r m i n i n g the absolute age of a b o n e . T h e isotopic abundances are l o w so the accelerator mass spectrometric approach ( A M S ) has b e e n u s e d to m a k e the measurements of C a - 4 1 . W h e r e the a p p l i c a t i o n of carbon d a t i n g to the d e t e r m i n a t i o n of the age of bone r e q u i r e s the s u r v i v a l of some of the proteinaceous matter (e.g. collagen), the inorganic p o r t i o n of
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the b o n e , w h i c h contains the c a l c i u m , survives m o r e r e a d i l y . C o n t a m i n a t i o n of the a m i n o a c i d fraction i n b o n e samples is another p r o b l e m w i t h carbon dating w h i c h , it was reasoned, s h o u l d not be as great a p r o b l e m w h e n the inorganic m i n e r a l phase is u s e d to d e t e r m i n e the age. F i n a l l y , one of the reasons that r a d i o c a l c i u m d a t i n g can c o m p l e m e n t carbon d a t i n g is that the h a l f life of C a - 4 1 is longer (fy of about 1 0 years c o m p a r e d to C - 1 4 £y of 5 7 3 0 years). Taylor et a l . discuss the c u r r e n t status of the r a d i o c a l c i u m d a t i n g m e t h o d i n terms of the p o t e n t i a l p r o b l e m s i n c l u d i n g e n v i r o n m e n t a l a n d diagenetic effects. Archaeological Chemistry IV Downloaded from pubs.acs.org by 80.82.78.170 on 12/26/16. For personal use only.
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S o m e of the p o t e n t i a l p r o b l e m s w i t h u s i n g t h e i n o r g a n i c p o r t i o n o f bones for age d e t e r m i n a t i o n a n d for the discovery of the constituents of ancient diets are discussed i n C h a p t e r 18. T h i s chapter b y E l - K a m m a r , A l l e n , a n d H a n c o c k shows some o f the changes that occur w h e n bones are b u r i e d . T h e scanning e l e c t r o n microscope ( S E M ) a n d X - r a y diffractometer w e r e u s e d to show h o w n e w m i n e r a l phases, i n c l u d i n g some that contain c a l c i u m , can fill the voids left i n b o n e as the organic fraction decomposes. C o n t a c t b e t w e e n the b o n e a n d soil not only affects the major elements l i k e c a l c i u m , b u t the trace elements as w e l l . C o m p a r i s o n s b e t w e e n bones b u r i e d i n the N i l e d e l t a a n d bones of m u m m i e s that w e r e p r o t e c t e d f r o m d i r e c t contact w i t h the soil show v e r y clearly that diagenesis a n d contamination are p r o b l e m s w h e n the inorganic p o r t i o n o f the b o n e is analyzed. T h e photomicrographs show c l e a r l y that e v e n the i n t e r i o r regions of a bone can b e affected i f g r o u n d water is present. Part of the p r o b l e m w i t h u s i n g the m o r e d e v e l o p e d radiocarbon d a t i n g techniques w i t h b o n e samples is that, i n m a n y cases, the bones b e i n g s t u d i e d are too o l d . T h e l o n g e r half-life for the C a - 4 1 w i l l make it m o r e valuable for d e t e r m i n i n g the age of the p a l e o l i t h i c bones that are of great interest to anthropologists. I n C h a p t e r 19, R o b i n s , Sales, a n d O d u w o l e describe another t e c h n i q u e that appears to be valuable for e x t e n d i n g the dates of b o n e samples to materials o l d e r t h a n can b e o b t a i n e d w i t h the radiocarbon m e t h o d . T h i s is not, h o w e v e r , an absolute t e c h n i q u e based u p o n changes i n the isotopic ratios, b u t a t e c h n i q u e based u p o n changes i n the e l e c t r o n s p i n resonance ( E S R ) signal. T h e chapter describes some of the p r o b l e m s w i t h u s i n g this t e c h n i q u e , i n c l u d i n g the effects of temperatures o n the change i n the E S R spectrum.
Organic Residues and Fibers I n a n u m b e r of instances, organic materials other than those i n bones, shells, a n d t e e t h survive the ravages of t i m e . O n e of the m o r e i n t e r e s t i n g examples is the n e a r l y r o c k l i k e organic r e s i n c a l l e d a m b e r . L o n g n o t e d for its attractive color, this m a t e r i a l h a d great value. Because a m b e r is a r e s i n f r o m c e r t a i n plants, differences i n its c o m p o s i t i o n reflect the original plants. I n C h a p t e r 2 0 , L a m b e r t , L e e , W e l c h , a n d F r y e report o n t h e i r c o n t i n u i n g investigation
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Archaeological Chemistry IV Downloaded from pubs.acs.org by 80.82.78.170 on 12/26/16. For personal use only.
that is a i m e d at " f i n g e r p r i n t i n g " a m b e r f r o m different sources. T h i s chapter describes the use o f C - 1 3 n u c l e a r magnetic resonance ( N M R ) spectroscopy for the characterization of a m b e r . C h a p t e r 20 reports that a m b e r from two M e x i c a n sites are similar to each other. T h e s e results differ from results o b t a i n e d for B a l t i c a n d D o m i n i c a n amber. T h e focus o f most archaeological c e r a m i c studies has b e e n o n p r o v e n a n c e or technology. T h e r e is also a g r o w i n g b o d y o f specific evidence o n h o w the p o t t e r y was u s e d . C h a p t e r 21 b y B e c k , S m a r t , a n d O s s e n k o p describe the organic tars u s e d to l i n e ancient M e d i t e r r a n e a n amphoras. C h a p t e r 21 i n cludes a d e s c r i p t i o n of h o w the residues from a m p h o r a contents can be analyzed. A s i n most cases w h e r e u n k n o w n organic materials are e n c o u n t e r e d , the most p o w e r f u l analytical t e c h n i q u e is gas chromatography w i t h mass s p e c t r o m e t r i c detection ( G C - M S ) . T h i s t e c h n i q u e is expensive for the analysis of large n u m b e r s o f samples. B e c k et al. show the advantages of u s i n g s i m p l e r , less expensive methods l i k e F T I R a n d t h i n layer chromatography ( T L C ) . T h e s e techniques p r o v i d e speed a n d ease o f analysis. W h e n u s e d to investigate c o m p l e x m i x t u r e s l i k e the natural products e x a m i n e d b y B e c k et a l . , more extensive methods m a y b e r e q u i r e d to validate the findings. O n e of the most e x c i t i n g n e w techniques i n analytical c h e m i s t r y has b e e n the d e v e l o p m e n t of sensitive methods based o n i m m u n o l o g i c a l r e sponses. O n e of the m a i n advantages of i m m u n o l o g i c a l techniques is t h e i r h i g h selectivity, e v e n i n c o m p l e x matrices. T h i s approach has made a d r a matic i m p a c t o n c l i n i c a l c h e m i s t r y . A s n e w probes are d e v e l o p e d , they w i l l p r o b a b l y be a p p l i e d to ancient proteinaceous materials. R a d i o i m m u n o a s s a y techniques are capable of m e a s u r i n g as little as 10~ g of p r o t e i n i n fossils. Because bone collagen is somewhat species-specific b y v i r t u e of its n o n h e l i c a l ends, the system has p o t e n t i a l for clarifying the p h y l o g e n y of h u m a n s . L o w e n s t e i n has d e v e l o p e d antisera i n rabbits capable of establishing the i m m u n o l o g i c a l distance ( I . D . ) b e t w e e n h u m a n s , p y g m y a n d c o m m o n c h i m p , rhesus m o n k e y , g u i n e a p i g , dog, cat, calf, a n d m o u s e (13). B y u s i n g the collagen I . D . L o w e n s t e i n suggested that h u m a n s a n d c h i m p s are close to each other, as are rats, m i c e a n d g u i n e a pigs. T h e s e techniques w e r e t h e n u s e d to test a n t i h u m a n a n d a n t i c h i m p sera against a series of six h o m i n i d fossils r a n g i n g i n age from 1000 (Hungary) to 1,900,000 (Omo) years o l d . It was d i s c o v e r e d that i m m u n o l o g i c a l activity decreased w i t h t i m e a n d c h a n g e d from b e i n g h u m a n l i k e to b e i n g c h i m p l i k e i n the t i m e p e r i o d b e t w e e n C r o - M a g n o n a n d N e a n d e r t h a l . These experiments d e m onstrated that i m m u n o l o g i c a l l y reactive collagen fragments persist i n 2 - m i l l i o n - y e a r - o l d fossils and e x h i b i t species-specific antibody b i n d i n g . 12
R a d i o i m m u n o a s s a y techniques may a i d i n clarifying genetic r e l a t i o n ships i f sufficient i m m u n o l o g i c a l activity is m a i n t a i n e d i n archaeological bones. I n C h a p t e r 22, H e r r , B e n j a m i n , a n d W o o d w a r d discuss some n e w i m m u n o l o g i c a l tests that can d i s t i n g u i s h b e t w e e n b l o o d a n d tissue of h u m a n
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a n d a n i m a l o r i g i n . A l t h o u g h the p r o b e d e s c r i b e d b y H e r r has not b e e n u s e d to examine any archaeological samples, it is i n c l u d e d i n this v o l u m e because it p r o v i d e s a valuable o v e r v i e w o f the field. T h e r e v i e w of this r a p i d l y d e v e l o p i n g field w i l l be valuable to archaeologists as n e w probes are d e v e l o p e d that c o u l d p r o v i d e n e w insight into archaeological p r o b l e m s . T h i s t e c h n i q u e may soon p r o v i d e m o r e specific genetic i n f o r m a t i o n , e v e n w i t h small amounts of p r e s e r v e d D N A i n hair a n d i n other proteinaceous m a t e r i a l that survives as part of the archaeological r e c o r d . I n C h a p t e r 22, H e r r et a l . describe a m o n o c l o n a l antibody u s e d to test for h u m a n a l b u m i n i n b o d y fluids. T h e d e v e l o p m e n t of this m o n o c l o n a l a n t i b o d y was a i m e d at forensic evidence, b u t i f (and it m u s t be tested) degradation processes do not destroy the antigenic site that this a n t i b o d y recognizes, it c o u l d b e used for archaeological samples. C e r t a i n l y as these techniques are d e v e l o p e d t h e y w i l l prove valuable i n the studies of objects that are suspected of c o n t a i n i n g b l o o d . F o r example, these n e w e r methods c o u l d h e l p further define an artifact l i k e the S h r o u d of T u r i n , w h i c h is d e s c r i b e d i n C h a p t e r 23. I n C h a p t e r 2 3 , D i n e g a r , A d l e r , a n d J u m p e r present a s u m m a r y of the k n o w n history a n d the earlier scientific examination of the famous religious artifact k n o w n as the S h r o u d of T u r i n . O n the basis of the previous i n t e r pretations of the changes i n the cellulose fibers a n d the b l o o d stains, a p l a n is p r e s e n t e d for m o r e specific testing u s i n g i m p r o v e d techniques. T h e a u thors propose that other tests be m a d e at the same t i m e that samples of the S h r o u d are b e i n g analyzed. A l t h o u g h these other tests m a y h e l p clarify the changes i n the fibers of this historical textile, the real test of its a n t i q u i t y w i l l b e the radiocarbon analysis. N e v e r t h e l e s s , the c o n t i n u e d progress o n the analysis of natural fibers w i l l p r o v i d e m o r e d e t a i l o n the changes that account for the b o d y images a n d stains o n the S h r o u d . (The image is i n t e r p r e t e d as h a v i n g b e e n the result of an o x i d a t i o n - d e h y d r a t i o n reaction.) I n a d d i t i o n , study of the S h r o u d may a i d conservationists as t h e y attempt to better u n d e r s t a n d natural aging processes and find ways to preserve these more fragile artifacts. B a l l a r d , K o e s t l e r , B l a i r , a n d I n d i c t o r discuss some of the p r o b l e m s w i t h the p r e s e r v a t i o n of silk i n C h a p t e r 24. T h e i r w o r k was a i m e d at u n d e r s t a n d i n g h o w various components a d d e d to the silk d u r i n g the m a n u f a c t u r i n g of a n u m b e r of historical flags affected the e m b r i t t l e m e n t a n d d e c o m p o s i t i o n of the material. T h e y f o u n d that colorants a n d chemicals a d d e d to w e i g h t the natural silk fibers c o u l d be detected b y u s i n g X - r a y fluorescence. T h e y correlated the inorganic additives to the deterioration of the flags. O n the other h a n d , organic silk itself is the subject o f C h a p t e r 25 b y H e r s h , T u c k e r , a n d B e c k e r . A n u m b e r of historical silk fibers w e r e e x a m i n e d i n o r d e r to u n d e r s t a n d the c h e m i s t r y of the degradation process. T h e roles of p h o t o c h e m i c a l processes as w e l l as heat are discussed. T h e c h e m i c a l processes of aging are c o m p l e x a n d slow. E i t h e r historical samples m u s t b e
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s t u d i e d , or methods m u s t be f o u n d to r e l i a b l y accelerate the aging process i n the laboratory. T h e e v e n t u a l object o f the studies p r e s e n t e d i n C h a p t e r s 24 a n d 25 is to p r o v i d e better ways to p r e s e r v e the silk artifacts.
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I n C h a p t e r 26, Jakes a n d A n g e l show that the analysis of e l e m e n t a l concentrations can also a i d i n the study of ancient textiles. I n this chapter, the inorganic components a n d t h e i r d i s t r i b u t i o n s i n the fibers w e r e the basis of a m e t h o d to identify the fibers. Jakes a n d A n g e l u s e d a scanning e l e c t r o n microscope to image the fibers m o r p h o l o g y , a n d energy dispersive X - r a y spectrometry to d e t e r m i n e e l e m e n t a l distributions. T h i s approach is suitable for the v e r y small samples often e n c o u n t e r e d as archaeological fibers. I n e a r l i e r w o r k , Jakes a n d coworkers have s h o w n that it is not always necessary for the organic fibers to survive i n o r d e r to o b t a i n i n f o r m a t i o n o n the textile. C h a p t e r 27 b y Jakes, S i b l e y , Kuttruff, W i m b e r l e y , M a l e c , a n d B a j a m o n d e discusses the i m p r i n t s or p s e u d o m o r p h s of fabrics that are m a d e w h e n m e t a l salts replace the d e c o m p o s i n g organic matrix. I n this research the m e t a l p s e u d o m o r p h s w e r e f r o m b r o n z e weapons that are over 3000 years o l d . Jakes et a l . u s e d photomicrographs to observe the m a n n e r i n w h i c h the y a r n was w o v e n to p r o d u c e the o r i g i n a l fabric. T h e statistical methods that w e r e u s e d to identify a n d correlate the patterns i n these textile p s e u d o m o r p h s are v e r y s i m i l a r to those o r i g i n a l l y u s e d i n provenance studies of the less fragile stone a n d pottery artifacts. T h i s study shows the i m p o r t a n c e that c o m p u t e r s a n d statistical methods have attained i n a i d i n g i n the o r ganization of the extensive data sets generated as a part o f archaeological studies.
Conclusions These examples of h o w chemists c o n t r i b u t e to archaeology are not i n t e n d e d to p r o v i d e a c o m p l e t e r e v i e w o f the field. T h e purpose of this chapter was to indicate h o w the field has m a t u r e d . I n some of the earlier w o r k , the analysis of i n o r g a n i c artifacts took m o r e of a " s h o t g u n " approach. It was thought that the p r o b a b i l i t y of differentiating b e t w e e n materials was e n h a n c e d b y a n a l y z i n g for a large n u m b e r of elements. F o r this reason, m u l t i e l e m e n t techniques w i t h p r o v e n accuracy l i k e n e u t r o n activation analysis w e r e favored. G r o u p i n g artifacts o n the basis of c h e m i c a l similarities l e d to increased use of various statistical protocols (computer programs). H o w e v e r , as different types of artifacts w e r e s t u d i e d (by c h e m i c a l means), i t b e c a m e increasingly clear that a m o r e d e t a i l e d u n d e r s t a n d i n g of the materials t h e m selves m a d e i t m o r e l i k e l y that useful archaeological i n f o r m a t i o n c o u l d b e obtained. M o r e d e t a i l e d studies, u s i n g an e v e r w i d e r array of analytical t e c h n i q u e s , have increased o u r u n d e r s t a n d i n g of m a n y natural materials a n d o f the early technologies. T h i s greater u n d e r s t a n d i n g of the materials p r o v i d e s a b e t t e r rationale for the choice of samples a n d techniques to be u s e d . T h e
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chapters i n this v o l u m e reflect the d i v e r s i t y of materials b e i n g s t u d i e d . I n each chapter, there has b e e n an attempt to u n d e r s t a n d the m a t e r i a l itself as w e l l as to increase o u r k n o w l e d g e of the past.
Archaeological Chemistry IV Downloaded from pubs.acs.org by 80.82.78.170 on 12/26/16. For personal use only.
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