Determination of Elemental Distribution in Ancient Fibers - Advances

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Determination of Elemental Distribution in Ancient Fibers Kathryn A. Jakes and Allen Angel 1

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Department of Textiles and Clothing, Ohio State University, Columbus, O H 43210 Center for Advanced Ultrastructural Research, University of Georgia, Athens, G A 30602

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Archaeological textiles can provide a vast body of evidence for prehistoric environments, cultures, and technologies. They may contain clues to the processes of degradation, alteration, or mineralization that occurred after burial. Determination of elemental composition and distribution within fiber structures can contribute to the understanding of biological, systemic, and diagenetic contexts of ancient textiles. A technique suitable for brittle, fragile, and very small samples of archaeological fibers was developed, in which fibers were freeze fractured, freeze dried, mounted in carbon paste, and analyzed with a scanning electron microscope coupled to an energy-dispersive spectrometer. Elemental content and distribution in cross sections of fibers have implications for identification of fibers, description of fiber processing, determination of fabrication technology, and elucidation of the history of the fiber in long-term storage or burial.

FABRICS THAT ARE RECOVERED FROM ARCHAEOLOGICAL SITES

are often so b a d l y d e g r a d e d that fiber identification o n the basis of p h y s i c a l m o r p h o l o g y is difficult. T h e changes that o c c u r d u r i n g diagenesis destroy p h y s i c a l a n d c h e m i c a l e v i d e n c e that is necessary to d i s c e r n fiber information. O n the o t h e r h a n d , the changes that o c c u r d u r i n g diagenesis, as w e l l as those that o c c u r at any stage of the fiber's l i f e t i m e , leave a r e c o r d w i t h i n the fiber's c h e m i c a l a n d p h y s i c a l structure, such that the altered fiber reflects its h i s tory. F i b e r s are not i n e r t , b u t interact w i t h t h e i r surroundings i n b o t h subtle

0065-2393/89/0220-0451$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

Allen; Archaeological Chemistry IV Advances in Chemistry; American Chemical Society: Washington, DC, 1989.

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and obvious ways. Just as a fiber exposed to an intense stress, such as i m m e r s i o n i n a solvent, w i l l r e s p o n d to the stress b y absorbing the c h e m i c a l , s w e l l i n g , a n d d i s s o l v i n g o r d e c o m p o s i n g , a fiber reacts i n response to a less intense stress w i t h s m a l l e r changes i n c h e m i c a l a n d p h y s i c a l structure. T h e result of the stress may not b e apparent u n t i l the perturbations accumulate over a l o n g t i m e . T h u s , a textile h a n g i n g u n s u p p o r t e d w i l l , over t i m e , show evidence of m o l e c u l a r c r e e p , a n d a fiber stored for a l o n g t i m e i n a p o l l u t i n g e n v i r o n m e n t m a y change color because of absorbed sulfur a n d n i t r o g e n oxides. D e g r a d e d fibers m a y b e difficult to identify b y the standard techniques p r e s c r i b e d for m o d e r n materials, b u t t h e i r structures offer valuable clues to the conditions of the fiber's g r o w t h (the biological context), to fiber p r e p a ration a n d fabric processing technology, to fabric use (the systemic or c u l t u r a l context), a n d to the conditions of b u r i a l or l o n g - t e r m storage (the diagenetic context). Information m u s t be extracted from the fibers c h e m i c a l a n d p h y s ical structure to i n t e r p r e t what the clues indicate. T h e goals of o u r w o r k were 1. to d e v e l o p a t e c h n i q u e that u s e d energy-dispersive analysis of X - r a y s that was appropriate for p r e p a r a t i o n , e l e m e n t a l analysis, a n d m a p p i n g the e l e m e n t a l d i s t r i b u t i o n of small, fragile fiber samples, t y p i c a l of those r e c o v e r e d f r o m archaeological sites (or of a size s m a l l e n o u g h to be m i n i m a l l y destructive of artifacts i n collections) 2. to d e t e r m i n e the e l e m e n t a l content a n d d i s t r i b u t i o n of a group of samples r e p r e s e n t i n g a b r o a d s p e c t r u m of fiber types a n d histories 3. to explore the i m p l i c a t i o n s of the analytical results for i n t e r p r e t a t i o n of the b i o l o g i c a l , systemic, a n d diagenetic contexts of archaeological a n d historical materials.

Experimental Details Samples.

F i b e r samples w e r e selected from a variety of sources to

represent a range of fiber types, a variety of conditions of l o n g - t e r m storage or b u r i a l , a n d a variety of ages. T h e samples w e r e 1. m o d e r n w o o l , Testfabrics N o . 522 2. m o d e r n l i n e n , Testfabrics N o . L - 5 3 3. m o d e r n silk, Testfabrics N o . 601 4. w o o l t u n i c , C o p t i c , ca. A . D . 200 5. hair fiber, Paracas 500 B . C . - A . D . 150, catalog N o . 382-37


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6. bast fibers, E t o w a h M o u n d C , G e o r g i a , ca. A . D . 1200, catalog N o . 840 7. bast fibers, E t o w a h M o u n d C , G e o r g i a , ca. A . D . 1200, catalog N o . 1145 8. feathers, E t o w a h M o u n d C , G e o r g i a , ca. A . D . 1200, catalog


No.

1145

9. m e t a l - w r a p p e d l i n e n , T u r k e y , 15th c e n t u r y , catalog T S M 13.1919 10. m e t a l - w r a p p e d s i l k , I t a l y , 1 5 t h c e n t u r y , c a t a l o g M M A 46.156.134 M a n y of the fabric structures f r o m w h i c h these samples w e r e taken have b e e n d e s c r i b e d i n other publications (1-3). I n e x p e r i m e n t i n g w i t h a p p r o priate methods for p r e p a r a t i o n of samples for e l e m e n t a l analysis, fibers are of l i m i t e d value because t h e y cannot be p r o v e n to b e l o n g to the textile object i n the box. F o r e x p e r i m e n t a l purposes, these fabrics s e r v e d w e l l as r e p r e sentative b r i t t l e , fragile, a n d m i n u t e fibrous samples for p r e p a r a t i o n a n d analysis.

Materials. F i b e r s w e r e r a p i d l y frozen o n a l i q u i d - n i t r o g e n - c o o l e d block, t h e n fractured several times w i t h a p r e c o o l e d razor blade. T h e fibers w e r e p l a c e d i m m e d i a t e l y i n a h i g h - v a c u u m evaporator ( N R C ) to freeze-dry o v e r n i g h t to sublimate any existing water a n d to p r e v e n t condensation o v e r the surface of the samples after freezing. (Such condensation of w a t e r c o u l d result i n e l e m e n t a l translocation.) F i b e r s w e r e treated i n this m a n n e r to p r o d u c e smooth, flat cross sections, a r e q u i r e m e n t for e n e r g y - d i s p e r s i v e spectrometry ( E D S ) of X - r a y s a n d X - r a y m a p p i n g . E a c h fractured fiber was m o u n t e d i n a 1-mm h o l e d r i l l e d into a carbon p l a n c h e t ( S P I , W e s t C h e s t e r , PA). T h e fibers w e r e first affixed w i t h p u r e carbon paste ( S P I , W e s t C h e s t e r , PA), t h e n o r i e n t e d i n an u p r i g h t p o s i t i o n to a l l o w at least 0.5 m m of fiber to e x t e n d out of the hole, such that the fractured plane was p a r a l l e l to the surface of the planchet. T h e samples w e r e t h e n coated w i t h a p p r o x i m a t e l y 40 n m of carbon b y u s i n g h i g h - v a c u u m evaporative techniques. A scanning e l e c t r o n m i c r o s c o p e (Philips 505) e q u i p p e d w i t h four s c i n tillator-type backscattered e l e c t r o n detectors a n d an e n e r g y - d i s p e r s i v e X ray microanalysis system (Tracor N o r t h e r n 5500) w e r e u s e d to analyze the specimens. Method. F i r s t , fibers w e r e e x a m i n e d for morphology. I f a smooth fractured plane was present a n d o r i e n t e d to allow visualization of the e n t i r e cross section, t h e n 5 0 - n m spot X - r a y analyses w e r e o b t a i n e d from a n u m b e r of points at the p e r i p h e r y of the section a n d its center. Samples w e r e i r r a -


454



d i a t e d for 5 0 - 5 0 0 s a n d spectra c o l l e c t e d at 25 k V . S e v e r a l fibers of each type from a g i v e n p l a n c h e t w e r e analyzed. W h e n spectra i n d i c a t e d e l e m e n t a l variation over the span of the cross section, or the presence of elements w i t h atomic n u m b e r s h i g h e r than F e , backscattered e l e c t r o n i m a g i n g was u s e d to qualitatively assess the d i s t r i b u t i o n a l v a r i a t i o n of these elements a n d possible sites at w h i c h some e l e ments h a d a c c u m u l a t e d . Because the signal f r o m backscattered electrons increased w i t h atomic w e i g h t , accumulations of specific elements c o u l d b e d e t e r m i n e d b y the i n t e n s i t y of the signal. Backscattered e l e c t r o n i m a g i n g was not p e r f o r m e d o n samples that w e r e p r i m a r i l y organic. I f spot analyses or backscattered i m a g i n g s h o w e d e l e m e n t a l variations, X - r a y maps w e r e o b t a i n e d to d e t e r m i n e the d i s t r i b u t i o n of a single e l e m e n t i n each fiber. Specific regions of spectra w e r e defined, and maps c o r r e s p o n d i n g to these energy regions w e r e made. T o ensure that data came f r o m the sectioned fiber a n d not from other r a n d o m locations o n the planchet, maps of the w h o l e s p e c t r u m , d e f i n e d as an energy r e g i o n , w e r e o b t a i n e d . X - r a y maps w e r e c o l l e c t e d w i t h d w e l l times of 0 . 2 - 0 . 3 s a n d 256- X 256p i x e l r e s o l u t i o n . A d i g i t a l secondary e l e c t r o n or backscattered e l e c t r o n image usually was made for v i s u a l c o m p a r i s o n a n d overlap w i t h the e l e m e n t a l maps. F u r t h e r details of the t e c h n i q u e are r e p o r t e d i n reference 4.

Results A l t h o u g h freeze-fracturing, f r e e z e - d r y i n g , a n d E D S analysis w e r e generally satisfactory, some difficulties w e r e e n c o u n t e r e d because of the nature of the fiber samples. F i r s t , not a l l of the samples fractured smoothly, n o r d i d a l l of the fibers i n one sample display smooth, flat cross sections. Because the X - r a y m i c r o a n a l y t i c a l t e c h n i q u e r e q u i r e s a flat surface geometry to obtain accurate counts, this was the surface type selected from each fiber sample e x a m i n e d . A l t h o u g h different fiber fracture tips may indicate different causes of degradation (5, 6), i t was assumed that any of the fibers of a y a r n selected for e l e m e n t a l analysis w e r e representative of a l l of the fibers i n the y a r n b u n d l e . Because the fibers e x a m i n e d i n each sample w e r e sectioned f r o m a single y a r n , i t was assumed that the fibers i n the y a r n e x p e r i e n c e d the same conditions throughout t h e i r lifetimes, except for some possible v a r i a t i o n i n g r o w t h conditions. I n further w o r k , m a n y m i c r o s i z e d samples c o u l d b e exa m i n e d b y the t e c h n i q u e d e s c r i b e d i n this chapter to d e t e r m i n e the extent of v a r i a t i o n w i t h i n a single y a r n . A d d i t i o n a l difficulties i n e l e m e n t a l analysis o c c u r r e d w i t h fibers that w e r e c o m p l e t e l y or p r i m a r i l y organic. T h e e l e m e n t a l spectra o b t a i n e d for these fibers d i s p l a y e d a b r o a d b a n d t y p i c a l of hydrocarbons, a n d no e l e m e n t a l maps c o u l d b e d e t e r m i n e d . F i n a l l y , fibers w i t h e x t r e m e l y fine structures, such as the feather s a m p l e , h i n d e r e d e l e m e n t a l m a p p i n g e v e n w h e n t h e y contained elements heavy


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e n o u g h to be c o u n t e d b y E D S analysis. T h e s e materials w o u l d heat u p a n d m o v e u n d e r the X - r a y b e a m . C o n s e q u e n t l y , an inside s p o t - o u t s i d e spot c o m p a r i s o n a n d backscattered e l e c t r o n i m a g i n g h a d to b e r e l i e d u p o n , r a t h e r than an e l e m e n t a l m a p , to get e l e m e n t a l d i s t r i b u t i o n i n f o r m a t i o n . D a t a o b t a i n e d i n the E D S analyses are l i s t e d i n T a b l e I. T h e fiber standards ( p r i m a r i l y organic ) gave b r o a d E D S spectra. N o heavy e l e m e n t a l c o m p o s i t i o n was i n d i c a t e d i n silk, a n d o n l y a s m a l l q u a n t i t y of c a l c i u m c o u l d b e d e t e c t e d i n l i n e n . N o e l e m e n t a l maps c o u l d b e o b t a i n e d for silk or l i n e n . T h e E D S spectra o f w o o l reflected its sulfur content. I n some of the samples, the somewhat h i g h e r concentration of sulfur i n one-half o f the cross section, w h i c h is expected o f this naturally b i c o m p o n e n t fiber, was apparent (7). I n o t h e r samples, the differentiation was not clear.

Table I. Elemental Components and T h e i r Locations i n Archaeological and Historical F i b e r Samples Element

Penetrating Surface Layer

Ca

382.37

Cu

EMC EMC

840 1145°

Fe

EMC EMC EMC EMC

840 1145, core 1145, feather 1145, feather

Ρ

Κ Ag S

fl

Throughout Fiber Modern linen E M C 840 E M C 1145, feather E M C 1145, core M M A 46.156.134 T S M 13.1919 Coptic tunic E M C 1145, core E M C 1145, feather E M C 840

E M C 1145, core E M C 840 E M C 1145, feather E M C 1145, feather E M C 1145, core T S M 19.19 Modern wooP 382.37 E M C 840 E M C 1145, feather E M C 840 E M C 1145, feather E M C 1145, core

3

6

Si

NOTES: E M C means Etowah Mound C. The samples are described under "Experimental Methods". The only elements found on the surface were Ca and Si, found only on hair fiber 382.37. Permeating throughout but somewhat larger concentration in sur face layer. ^Somewhat heavier concentration in one-half of the cross section. a



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T h e Paracas h a i r fiber s h o w n i n F i g u r e 1 fractured cleanly. I n some cases, the E D S maps r e v e a l e d a h i g h e r concentration of sulfur i n o n e - h a l f of the cross section, similar to the sulfur d i s t r i b u t i o n of w o o l (see F i g u r e 2). K , S i , a n d C a w e r e f o u n d o n the fiber edges o n l y (Figures 2 a n d 3). I n m a n y cases, t h e y w e r e c l u m p e d together o n the fiber surface i n a m a n n e r that i n d i c a t e d soil aggregation. N o p e n e t r a t i o n of these elements into the fiber surface was seen. I n the E D S maps of the C o p t i c w o o l fiber, the sulfur a n d c a l c i u m w e r e e v e n l y d i s t r i b u t e d throughout the fiber.

Figure 1. Hair fiber from Paracas (ca. A.D. 200); magnification: 2230 X.

Figure 2. Elemental dot map of Paracas hair fiber indicating distribution sulfur (left) and potassium (right). Allen; Archaeological Chemistry IV Advances in Chemistry; American Chemical Society: Washington, DC, 1989.

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Figure 3. Elemental dot map of Paracas hair fiber indicating distribution silicon (left) and calcium (right).

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of

T h e feather w r a p p i n g of E t o w a h M o u n d G ( E M C ) 1145 c o n t a i n e d A l , S i , P, S, C l , K , C a , F e , a n d C u . T h e i n s i d e s p o t - o u t s i d e spot e l e m e n t a l c o m p a r i s o n i n d i c a t e d that the outer edge of each feather b a r b u l e c o n t a i n e d m o r e F e a n d Ρ t h a n the i n s i d e . T h e backscattered e l e c t r o n image c o r r o b orated this point. T h e outer r i m of the feathers appeared b r i g h t e r because of the greater concentration o f i r o n , a fact i n d i c a t i n g that i r o n h a d p e n e t r a t e d o n l y into the surface of the feathers. A l , S i , S, C l , K , C a , a n d C u w e r e d i s t r i b u t e d t h r o u g h o u t the material. A m i c r o g r a p h of E M C 1145 core is s h o w n i n F i g u r e 4, the backscattered image is s h o w n i n F i g u r e 5, a n d the e l e m e n t a l dot maps are s h o w n i n F i g u r e 6. T h e bast fibers, E M C 1145 core, a n d E M C 840, have similar spectra, and c o n t a i n e d A l , S i , P, S, K , C a , F e , a n d C u . E M C 1145 also c o n t a i n e d some C I . T h e E D S maps of these materials indicate that b o t h materials c o n t a i n e d h i g h e r concentrations of i r o n i n t h e i r outer surface layers a n d h a d c a l c i u m a n d c o p p e r d i s t r i b u t e d throughout. Phosphorus a n d sulfur w e r e c o n f i n e d to the fiber's i n t e r i o r . A s w i t h the feathers, the backscattered elec t r o n image of these materials reflected the i r o n concentrated i n the surface layers. E l e m e n t a l maps of the m e t a l - w r a p p e d l i n e n ( T S M 13.1919) s h o w e d that the m e t a l w r a p p i n g was silver, b u t the fibers i n the y a r n also c o n t a i n e d some silver a n d c a l c i u m . T h e maps of the m e t a l - w r a p p e d silk ( M M A 46.156.134) show that the m e t a l w r a p p i n g was gold-coated silver, a n d that c a l c i u m was present i n the fibers b u t not silver. Potassium was present i n b o t h the m e t a l w r a p p i n g a n d the fiber core. T h e m e t a l surface of the m e t a l - w r a p p e d silk showed a v a r i a t i o n i n c o l oration i n the backscattered image, a n d this variation reflected the variable c o m p o s i t i o n of the surface layer ( F i g u r e 7). T h e e l e m e n t a l m a p shows areas w h e r e silver b r o k e t h r o u g h the g o l d coating. W i t h no other heavy elements present, it is assumed that these layers w e r e silver oxides. Allen; Archaeological Chemistry IV Advances in Chemistry; American Chemical Society: Washington, DC, 1989.


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Figure 4. Bast fiber from Etowah Mound 1145 core (ca. A.D. 1200). Secondary electron image; magnification: 1200 X .

Figure 5. Bast fiber from Etowah Mound 1145 core (ca. A.D. 1200). Backscattered electron image; magnification: 345 x .



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Figure 6. Elemental dot map of bast fiber, Etowah Mound C 1145 core, indicating distribution of iron (left) and copper (right).

Figure 7. Metal-wrapped silk from Italy (15th century). Backscattered electron image; magnification: 686 X .


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ARCHAEOLOGICAL CHEMISTRY

Discussion


T h e i n t e r a c t i o n o f fibers w i t h t h e i r e n v i r o n m e n t is often s t u d i e d b y o b s e r v i n g the changes i n p h y s i c a l a n d c h e m i c a l structure as reactions occur. T y p i c a l changes s t u d i e d are increase i n o x i d i z e d or unsaturated groups, decrease i n degree o f p o l y m e r i z a t i o n , decrease i n tensile strength, a n d changes i n m o r phology. A n o t h e r w a y to m o n i t o r the i n t e r a c t i o n of fibers w i t h the e n v i r o n m e n t is to d e t e r m i n e w h i c h c o m p o u n d s are absorbed or adsorbed i n t o the fibers. F i b e r s can b e a l t e r e d b y sorption of or reaction w i t h h y d r o c a r b o n s , s u c h as soils; h o w e v e r , this w o r k focused o n c o m p o u n d s that c o n t a i n e d h e a v i e r e l e m e n t s , because of t h e i r m o r e obvious differences f r o m the h y d r o c a r b o n structure of fibers. E n e r g y - d i s p e r s i v e analysis of X - r a y s was the chosen analytical m e t h o d because of its sensitivity to e l e m e n t s h e a v i e r t h a n s o d i u m , its capability o f m a p p i n g e l e m e n t a l d i s t r i b u t i o n , a n d its capacity for c o m b i n a t i o n w i t h a scanning e l e c t r o n microscope. E D S microanalysis has b e e n r e p o r t e d to b e suitable for the d e t e r m i n a t i o n o f m o r d a n t treatments o n historical fibers (8-10) a n d has b e e n u s e d to characterize m e t a l w r a p p i n g s of c o m b i n a t i o n yarns (11-13). E D S microanalysis has also b e e n u s e d to d e t e r m i n e the c o m p o s i t i o n of p s e u d o m o r p h s a n d fibers i n the process of m i n e r a l r e p l a c e m e n t (13, 14, IS). I n this chapter, the results of past research are e x p a n d e d because fiber cross sections w e r e e x a m i n e d , r a t h e r than l o n g i t u d i n a l v i e w s of fibers, a n d distributions of elements w e r e o b t a i n e d i n a d d i t i o n to o v e r a l l e l e m e n t a l spectra. Because the X - r a y b e a m penetrates o n l y a small distance into the surface of a sample (approximately 8 - 1 0 μηι for a 2 5 - k V excitation ), ex a m i n a t i o n of a l o n g i t u d i n a l l y m o u n t e d fiber produces e l e m e n t a l spectra of surface layers o n l y . S u c h spectra may not be representative of the b u l k of the fiber. I n a d d i t i o n , this w o r k i m p r o v e s u p o n past research i n that the freeze-fracturing-freeze-drying E D S t e c h n i q u e is s u i t e d to v e r y s m a l l , frag i l e fiber samples (whether single fibers or small y a r n pieces), a n d is l i m i t e d i n size o n l y i n the o p e r a t o r s a b i l i t y to see a n d h a n d l e the samples. B y u s i n g this p r o c e d u r e , c o m p r e s s i o n o f the fiber cross section a n d e l e m e n t a l r e d i s t r i b u t i o n are a v o i d e d . T h e ability to v i s u a l i z e e l e m e n t a l content a n d the d i s t r i b u t i o n of those elements w i t h i n a fibers structure is p o t e n t i a l l y significant for the i n t e r p r e tation o f the b i o l o g i c a l , systemic, a n d diagenetic contexts of fibrous materials. I f fiber i d e n t i t y is questionable, E D S analysis can p r o v i d e some a d d i t i o n a l information. H a i r fibers contain a significant a m o u n t of sulfur, a n d that sulfur is somewhat m o r e concentrated i n one-half of the fibers' cross sections. T h i s b i c o m p o n e n t nature sometimes is apparent i n e l e m e n t a l maps and can b e useful i n i d e n t i f y i n g w o o l or hair. Because silica and c a l c i u m oxalate crystals f o r m i n p l a n t materials as t h e y grow, o v e r a l l d i s t r i b u t i o n o f large amounts of s i l i c o n or c a l c i u m indicates bast fibers. T h i s d i s t r i b u t i o n can r e a d i l y b e d i s t i n g u i s h e d f r o m l o c a l i z e d soil c o n t a m i n a t i o n o n fiber surfaces; the larger


26.

JAKES & A N G E L

Elemental Distribution

in Ancient Fibers

461


concentration excludes the possibility that the presence of c a l c i u m is due to residual soap s c u m . W h e n c a l c i u m oxalate a n d silica crystals are i n d i c a t e d b y E D S , further study of these crystals a n d t h e i r shape may a i d fiber i d e n tification. T h e s e crystals, also called p h y t o l i t h s , do not degrade after b u r i a l a n d so p r o v i d e an e n d u r i n g m o d e of plant identification w h e n the rest of the fiber is gone (16-18). E l e m e n t a l content and m a p p i n g also w i l l contribute to the u n d e r s t a n d i n g of the systemic context of fibrous materials. T h e m o d e r n l i n e n e x a m i n e d i n this w o r k contained a quantity of c a l c i u m that was too small i n comparison to the organic nature of the fiber to be m a p p e d . Possibly this c a l c i u m was the result of r e s i d u a l soap scum from cleaning. M o r e significant quantities of elements, such as c a l c i u m , m a g n e s i u m , a n d i r o n , w i t h i n the l i n e n or other bast fibers c o u l d indicate that the fiber was retted i n h a r d water. Because bast fibers can act as ion-exchange columns a n d attract m i n e r a l s , a n d because these ions c o u l d be m o r e concentrated i n the protoplasm l i n i n g the l u m e n , e l e m e n t a l m a p p i n g c o u l d p r o v i d e more e v i d e n c e c o n c e r n i n g bast fiber p r o cessing. O t h e r aspects of fiber-yarn-fabric treatment that can be i n d i c a t e d b y E D S analysis are d y e i n g w i t h mordants, w h i t e n i n g a n d d e l u s t e r i n g w i t h agents such as t i t a n i u m dioxide, a n d w e i g h t i n g of silk. T h e e l e m e n t a l maps w i l l reveal d e p t h of penetration of these treatments. E x a m i n a t i o n of the m e t a l - w r a p p e d yarns shows that E D S analysis a n d m a p p i n g can be used to infer y a r n structure (systemic contextual information) a n d l o n g - t e r m storage conditions (diagenetic contextual information). F i b e r s s u r r o u n d e d w i t h silver m e t a l s h o w e d absorbed silver ions; fibers s u r r o u n d e d w i t h gold-coated silver d i d not. A l t h o u g h some silver oxides w e r e present on the surface of the m e t a l w r a p p i n g , the inert gold coating or other e n v i r o n m e n t a l conditions h i n d e r e d silver ion m i g r a t i o n into this y a r n . T h e fibers, thus, reflect t h e i r l o n g - t e r m storage conditions. T h e s e fabrics have not b e e n b u r i e d , a n d have not b e e n subjected to l o n g - t e r m i m m e r s i o n i n water. R a t h e r , conditions of n o r m a l h u m i d i t y a n d t e m p e r a t u r e have b e e n sufficient for e l e m e n t a l transfer to the i n n e r fibers a n d for corrosion layers to form on the m e t a l wrappings. H a r d i n a n d Duffield (11) found sulfur-containing c o r rosion layers on the silver w r a p p i n g of 16th-century T u r k i s h c o m b i n a t i o n yarns a n d a t t r i b u t e d the sulfur source to b u r n i n g fossil fuels. E D S analysis of yarn cross sections c o u l d p r o v i d e additional i n f o r m a t i o n , a n d d o c u m e n t , for example, w h e t h e r sulfur from the air permeates the fibrous core as w e l l . S u c h is the case i n the " f u m e f a d i n g " of textiles e n c l o s e d i n e n v i r o n m e n t s w i t h sulfur a n d nitrogen oxides. E l e m e n t a l m a p p i n g of the fiber cross sections w o u l d show the d e p t h of penetration of the a b s o r b e d or adsorbed species, a n d perhaps indicate the l e n g t h of exposure, as w e l l as of exposure to gaseous rather than aqueous e n v i r o n m e n t s . T h e results of the analysis of materials e x a m i n e d i n this w o r k p a r t i c u l a r l y l e n d themselves to inferences of diagenetic context. Just as the m e t a l w r a p p e d yarns s h o w e d that m e t a l ions can transfer to fibers i n contact w i t h silver, fibers b u r i e d i n association w i t h c o p p e r reflect that association b y


462



t h e i r large c o p p e r content. A t present, it is b e l i e v e d that the c o p p e r is b o u n d to fiber cellulose or p r o t e i n p o l y m e r s . U n d e r appropriate conditions, h o w ever, the c o p p e r l o c a l i z e d w i t h i n the fiber structure w i l l oxidize to form c o p p e r m i n e r a l s s u c h as malachite a n d c u p r i t e . T h e r e s u l t i n g fiber p s e u d o m o r p h maintains the p h y s i c a l shape o f the fiber b u t no longer has its organic c o m p o s i t i o n (19, 20). T h e presence of S i , A l , P, C a , a n d Κ throughout the fibers from E t o w a h M o u n d is e v i d e n c e of the i n t e r a c t i o n b e t w e e n the fiber a n d soil i n a w e t e n v i r o n m e n t . T h e s e soil e l e m e n t s , as w e l l as c o p p e r i o n from the c o r r o d i n g c o p p e r m e t a l , r e a d i l y dissolve i n an o x i d i z i n g aqueous e n v i r o n m e n t a n d migrate w i t h w a t e r p e r c o l a t i n g t h r o u g h the g r o u n d . B y absorbing this g r o u n d water, b u r i e d fibers also absorb the dissolved elements. I r o n ions migrate o n l y u n d e r r e d u c i n g conditions, a n d therefore do not behave i n a m a n n e r s i m i l a r to the other soil elements. R a t h e r , m i c r o p a r t i culate i r o n is c a r r i e d b y the waters p e r c o l a t i n g t h r o u g h the site a n d deposits i n the fiber surface i n a m a n n e r comparable to rust staining of m o d e r n textiles. W h e t h e r the i r o n particles are m e c h a n i c a l l y e n t r a p p e d or are c o m p l e x e d i n some m a n n e r w i t h the fiber's organic structure has not b e e n d e t e r m i n e d , b u t the backscattered electron images of the fibers from E t o w a h M o u n d clearly show this t h i n l a y e r of i r o n penetration ( F i g u r e 5). I n contrast to the w e t , o x i d i z i n g conditions of the E t o w a h M o u n d , w i t h its i r o n - c o n t a i n i n g c l a y l i k e s o i l , the d r y conditions a n d l i m e s t o n e - t y p e soil of the Paracas p e n i n s u l a have r e s u l t e d i n fibers w i t h soil encrustations of silicon a n d c a l c i u m , b u t w i t h no absorbed soil elements. A n u n r e s o l v e d question remains c o n c e r n i n g the presence of significant quantities of sulfur i n the materials from E t o w a h M o u n d . N o t o n l y do the fibers contain sulfur, b u t c o p p e r sulfate corrosion layers are also present o n the associated c o p p e r m e t a l from these burials (21). Because sulfur is present i n the soil o n l y i n trace quantities, some other sulfur source must b e f o u n d . T h e source of the sulfur m a y b e a treatment of the textile o r m a y be a p r o d u c t of the d e c o m p o s i n g b o d y nearby. F u r t h e r examination other textiles f r o m these burials s h o u l d p r o v i d e answers to the questions of the source of sulfur.

Conclusions The freeze-fracturing, freeze-drying, E D S analysis, a n d m a p p i n g p r o c e d u r e was t a i l o r e d for the examination of b r i t t l e , fragile, a n d s m a l l fiber samples. E v a l u a t i o n of a group of fibers w i t h this t e c h n i q u e p r o d u c e d results that suggest a great p o t e n t i a l for p r o d u c i n g information that m a y c o n t r i b u t e to the u n d e r s t a n d i n g of the b i o l o g i c a l , systemic, a n d diagenetic contexts of archaeological a n d historical textiles. I n each of the cases d e s c r i b e d , m a n y implications for contextual i n f o r m a t i o n c o u l d be i n f e r r e d f r o m the data, b u t no conclusions c o u l d b e d r a w n for any of the materials e x a m i n e d because m a n y m o r e samples f r o m w e l l - d o c u m e n t e d sites n e e d to be s t u d i e d .


463 JAKES & A N G E L Elemental Distribution in Ancient Fibers E l e m e n t a l content a n d d i s t r i b u t i o n m a y be useful i n d e t e r m i n i n g b i o logical context (discussed h e r e o n l y i n terms of fiber identification), b u t further w o r k may suggest g r o w t h conditions of the fibers as w e l l . Inferences c o n c e r n i n g systemic contexts w e r e discussed, i n c l u d i n g fiber processing, d y e i n g , a n d finishing. F u r t h e r w o r k , p a r t i c u l a r l y e x a m i n i n g treated m o d e l fibers, w i l l c o n f i r m the speculations made h e r e . T h e d e f i n i t i o n of the d i agenetic contexts of archaeological materials made here can b e v e r i f i e d a n d e x p a n d e d w i t h the analysis of samples from fully d o c u m e n t e d sites. E x a m ination of soil, m e t a l , w o o d , or any other associated m a t e r i a l f r o m the sites m u s t b e i n c l u d e d as w e l l as evaluation of m o i s t u r e content, acidity, a n d oxidation p o t e n t i a l . A f t e r study of fully d o c u m e n t e d materials, patterns can b e d e d u c e d , i n c l u d i n g d e f i n i t i o n of those factors that persist t h r o u g h diage nesis a n d those that change i n p r e d i c t a b l e m a n n e r . F r o m these patterns, i t w i l l b e possible to examine fibers of u n k n o w n o r i g i n a n d to infer some information c o n c e r n i n g t h e i r b i o l o g i c a l , systemic, a n d diagenetic contexts. D e t e r m i n a t i o n of e l e m e n t a l content a n d m a p p i n g of e l e m e n t a l d i s t r i b u t i o n can m a k e an i m p o r t a n t c o n t r i b u t i o n to the u n d e r s t a n d i n g of archaeological and historical materials.


26

Acknowledgments W e are i n d e b t e d to L . R. S i b l e y o f the D e p a r t m e n t of Textiles a n d C l o t h i n g , O h i o State U n i v e r s i t y ; L . L a r s o n , State Archaeologist of G e o r g i a ; A . P a u l of the U n i v e r s i t y of Texas, A r l i n g t o n ; a n d D . M o t t of the F i n e A r t s D e p a r t m e n t of the U n i v e r s i t y of G e o r g i a for the donation of fiber samples. W e gratefully acknowledge the financial support of the C e n t e r for A d v a n c e d U l t r a s t r u c t u r a l R e s e a r c h a n d the C e n t e r for A r c h a e o l o g i c a l Sciences of the U n i v e r s i t y of G e o r g i a . K . Jakes also thanks J . D . Taylor a n d R. L . H a u s s for t h e i r encouragement d u r i n g the progress of this w o r k .

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R E C E I V E D for review June 11, 1987. A C C E P T E D revised manuscript A p r i l 18, 1988.


Determination of Elemental Distribution in Ancient Fibers - Advances

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