Archaeological Chemistry IV - American Chemical Society

20 Residues and Linings in Ancient Downloaded by UNIV OF ARIZONA on December 20, 2012 | http://pubs.acs.org Publication Date: July 1, 1989 | doi: 10.1021/ba-1988-0220.ch020

Mediterranean Transport Amphoras Curt W. Beck, Christopher J. Smart , and Dorreen J. Ossenkop 1

Amber Research Laboratory, Department of Chemistry, Vassar College, Poughkeepsie, ΝY 12601

Parallel analyses by IR, thin-layer chromatography (TLC), and gas chromatography-mass spectrometry (GC-MS) of organic remains adhering to shards of ancient amphoras excavated in the harbor of Carthage (Tunisia) identified these remains as pine pitches. Capillary GC of methylated acid fractions showed abietic acid, dehydroabietic acid, and 7-ketodehydroabietic acid as the principal components. Two-dimensional TLC of untreated ether extracts revealed abietic acid in 12 of 31 samples and dehydroabietic acid in 26 of 31 samples. IR spectra of solid, raw samples indicated the presence of isopropyl groups, characteristic of the abietane skeleton, in 80% of the samples. Rapid and convenient analysis by TLC and IR was, in most cases, sufficient to identify pine resin products even after extensive pyrolytic and oxidative degradation.

R.ESIDUES A N D LININGS IN ARCHAELOGICAL CERAMICS, p a r t i c u l a r l y i n the u n g l a z e d transport amphoras that s e r v e d as s h i p p i n g containers of the M e d iterranean Sea trade from the B r o n z e A g e to h i s t o r i c t i m e s , have l o n g b e e n k n o w n . U n t i l r e c e n t l y , the methods of analytical c h e m i s t r y p e r m i t t e d o n l y a cursory study a n d tentative identification of these c o m p l e x organic m i x tures. L i n i n g s are t h i n , continuous coatings a p p l i e d to the i n t e r i o r surface of an u n g l a z e d vessel to r e n d e r it i m p e r m e a b l e ; residues are the a l t e r e d remains o f the vessel's contents. I n the archaeological r e c o r d , b o t h residues P r e s e n t address: Department of Chemistry, Yale University, N e w H a v e n , C T 06520 0065-2393/89/0220-0369$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

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

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a n d l i n i n g s are loosely d e s c r i b e d as b e i n g r e s i n , r o s i n , p i t c h , tar, asphalt, or b i t u m e n w i t h o u t c h e m i c a l analysis a n d w i t h little regard to t h e precise meanings o f these terms.

Downloaded by UNIV OF ARIZONA on December 20, 2012 | http://pubs.acs.org Publication Date: July 1, 1989 | doi: 10.1021/ba-1988-0220.ch020

Definition of Terms Resin applies to natural exudations o f plants that have b e e n u s e d w i t h o u t i n t e n t i o n a l modification. I n archaeological contexts, h o w e v e r , resins m a y undergo changes. T h e l o w - m o l e c u l a r - w e i g h t , volatile, m o n o t e r p e n o i d c o m ponents o f oleoresins are r e a d i l y lost b y evaporation, a n d t h e water-soluble carbohydrate components o f gum resins w i l l certainly dissolve i f the object is exposed to water. A c c i d e n t a l exposure to fire leads to e v e n m o r e drastic p y r o l y t i c transformations that m a y n o t b e distinguishable f r o m transformations caused b y i n t e n t i o n a l heat treatment. T h u s a sample that was a r e s i n w h e n o r i g i n a l l y u s e d may have b e e n c o n v e r t e d to a p i t c h b y a catastrophic fire. Rosin is sometimes u s e d to refer to certain resins, especially the natural exudates o f fir a n d p i n e trees, a n d i n such designations as " r o s i n - t r e e " for the S o u t h A f r i c a n s h r u b Cineraria resinifera. Strictly speaking, r o s i n is t h e residue after distillation o f the volatile components o f the w h o l e r e s i n , again, especially o f fir a n d p i n e resins. T h e t e r m is synonymous to colophony. I n m o d e r n practice, c o l o p h o n y is o b t a i n e d b y v a c u u m distillation o f the volatile constituents o f r e s i n i n t h e absence of air. T h e p r o d u c t retains t h e t y p i c a l l y y e l l o w color o f the o r i g i n a l r e s i n . I n earlier t i m e s , t h e r e s i n was h e a t e d i n o p e n vessels a n d t h e p r o d u c t was b r o w n o r black a n d partially p y r o l y z e d ; it was, i n fact, p i t c h . Because o f this a m b i g u i t y , it is best to avoid t h e w o r d rosin altogether. Pitch is t h e r e s i d u e after t h e distillation o f volatile r e s i n components i n an o p e n vessel. T h e m a t e r i a l is t y p i c a l l y black a n d is referred to as pix b y R o m a n w r i t e r s (J). W h e n o b t a i n e d f r o m p i n e r e s i n , i t m a y b e c a l l e d pine pitch; w h e n o b t a i n e d f r o m other plant resins, it m a y b e c a l l e d m o r e generally wood pitch. T h e distillate o f r e s i n distillation is c a l l e d tar. Pine tar is f r o m p i n e r e s i n , a n d wood tar is from other p l a n t resins. Coal tar is made f r o m coal. T h e use o f tar i n a n t i q u i t y is u n c e r t a i n a n d u n l i k e l y (2). Bitumen is a loosely u s e d t e r m (3). It is best defined to m e a n " n a t i v e substances" (4) " c o m p o s e d p r i n c i p a l l y of hydrocarbons a n d substantially free of oxygenated b o d i e s " (5) that occur naturally as t h e heavy fraction o f p e troleum. Asphalt suffers f r o m t h e u n c e r t a i n t y o f m e a n i n g o f t h e G r e e k w o r d asphaitos a n d of its correspondence to related w o r d s i n ancient N e a r E a s t e r n languages (2). I n m o d e r n t e r m i n o l o g y t h e t e r m refers to a natural o r m a n ufactured m i x t u r e o f m i n e r a l fines a n d b i t u m e n .


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Previous Analyses O f these materials, r e s i n , p i t c h , a n d b i t u m e n are m e n t i o n e d i n t h e classical literature a n d are l i k e l y to b e f o u n d i n M e d i t e r r a n e a n archaeological c o n texts. B i t u m e n a n d asphalt f r o m N e a r E a s t e r n sites have b e e n s t u d i e d b y M a r s c h n e r a n d W r i g h t (6). T h e identification o f a w i d e variety o f resins i n archaeological a n d art h i s t o r i c a l contexts was p i o n e e r e d b y M i l l s a n d his c o w o r k e r s (7) at t h e R e s e a r c h L a b o r a t o r y o f the N a t i o n a l G a l l e r y i n L o n d o n . T h e B r i t i s h group a n d C o n d a m i n a n d F o r m e n t i (8) i n F r a n c e u s e d gas c h r o matography ( G C ) o f m e t h y l a t e d d i t e r p e n e r e s i n acids to identify p i n e p i t c h o n t h e r a m o f a C a r t h a g i n i a n w a r s h i p a n d i n transport amphoras, respect i v e l y . M o s t r e c e n t l y , Shaekley (9) r e p o r t e d t h e w o r k done b y M i l l s o n resinous deposits i n a 6 t h - c e n t u r y A . D . storage j a r from B o q e q (Israel). G C s h o w e d d e h y d r o a b i e t i c a c i d (structure 1) a n d 7-ketodehydroabietic a c i d (structure 2) b u t n o t abietic a c i d (structure 3). T h e identification o f i n d i v i d u a l r e s i n acids b y G C is w e l l established. T h e m e t h o d r e q u i r e s a considerable i n v e s t m e n t o f t i m e a n d e q u i p m e n t a n d is u n l i k e l y to b e u s e d for the large n u m b e r o f amphoras a n d a m p h o r a shards that have c o m e to l i g h t f r o m n u m e r o u s sites. A single s h i p w r e c k m a y w e l l

COOH

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p r o d u c e 500 to 1000 amphoras. C l e a r l y , m o r e r a p i d a n d s i m p l e methods of i d e n t i f y i n g resinous organic remains are n e e d e d . A suite o f shards of transport amphoras excavated b y the O r i e n t a l I n stitute of the U n i v e r s i t y of C h i c a g o , u n d e r the d i r e c t i o n of L . E . Stager, p r o v i d e d an o p p o r t u n i t y to test i n f r a r e d (IR) spectroscopy a n d t h i n - l a y e r chromatography ( T L C ) as q u i c k a n d easy methods of i d e n t i f y i n g the botanical sources o f resins a n d to compare the results o b t a i n e d w i t h these methods w i t h those o b t a i n e d b y G C a n d G C - m a s s spectrometry ( G C - M S ) .


The Amphora Shards T a b l e I lists the 31 shards u s e d i n this study. T h e i r fragmentary state made typological identification difficult a n d close d a t i n g i m p o s s i b l e . A c c o r d i n g to Wolff (10), seven of the shards date to the B y z a n t i n e p e r i o d ( 4 t h - 7 t h centuries A . D . ) , one is R o m a n ( l s t - 4 t h centuries A . D . ) , a n d the r e m a i n i n g 23 r e p resent P u n i c , G r e e k , G r a e c o - I t a l i c , C o r i n t h i a n , a n d u n i d e n t i f i e d types, r a n g i n g i n date from the 4 t h c e n t u r y B . C . to the e n d of the t h i r d P u n i c W a r i n 146 B . C . A s a g r o u p , the shards span m o r e than a m i l l e n n i u m . T h e n u m b e r of shards w i t h organic remains was a s m a l l fraction of the total. Thousands of shards f r o m the P u n i c p e r i o d w e r e collected, b u t fewer than 250 h a d any organic l i n i n g s or residues. A m o n g the shards of this p e r i o d , o n l y 8% of the C o r i n t h i a n t y p e , 5 % of the Graeco-Italic t y p e , a n d still smaller n u m b e r s for the other types h a d organic l i n i n g s or residues (10). T a b l e I also shows the nature of the organic r e m a i n s , as far as this c o u l d b e ascertained. I f the i n t e r i o r surface of a shard, a n d especially of a b o d y shard, was c o v e r e d w i t h a t h i n , continuous coating of resinous m a t e r i a l , the sample was classified as a l i n i n g . I f there was a substantial, compact deposit at the b o t t o m o r " t o e " of the vessel b u t no coating o n adjacent i n t e r i o r surfaces, the sample was classified as a residue. E i g h t samples c o u l d not b e classified because the e v i d e n c e was ambiguous. T w o samples from r i m s m a y have b e e n seals u s e d to l u t e the cover of the vessel o p e n i n g .

Materials and Methods I R Spectroscopy. Samples for IR spectroscopy were prepared by pressing 100mg K B r pellets containing 1 mg of sample. Samples were run both on a P e r k i n - E l m e r model 167 dispersive (grating) instrument and on a P e r k i n - E l m e r model 1750 Fourier transform difiractometer-model 7300 laboratory computer system. Only the latter instrument afforded the resolution needed to identify the skeletal frequencies of isopropyl groups. T L C Analysis. Two-dimensional T L C was carried out on Anasil-OF silica-onglass plates. A n ether solution of the crude sample was spotted on a plate, and the plate was developed twice with heptane to carry nonpolar components to the top edge of the plate. The acids remained at the origin and were separated by development of the plate perpendicular to the original direction with hep-



Sample No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Registration No. 12 627 12 644 12 628 12 625 12 641 12 677-80 12 635 5 131 12 640 12 637 12 636 12 639 6 857 12 643 11 124 11 127 12 645 12 046 11957 12 089 6 876 12 626 12 629 12 630 12 631 12 632 12 633 12 634 12 642 12 638 6 880

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Table I. List of Samples and Results of T L C and I R Analyses TLC Result Dehydroabietic Abietic Sample Amphora Amphora Acid Acid Type Part Type + Residue Toe Byzantine Late Punic? Toe Unidentified + + Graeco-Italic Toe Residue + + Graeco-Italic Body Lining + + Late Punic Body Unidentified _ Byzantine Toe and body Lining + Byzantine Toe Residue + + Corinthian Toe Lining + Unidentified Body Lining + + Toe Unidentified Byzantine + Byzantine Toe Residue + Roman Toe Residue + Graeco-Italic? Toe Residue Corinthian Upper body Lining + + Flat-top triangular Rim Unidentified + + Graeco-Italic Body Lining + Byzantine Toe Residue + Graeco-Italic? Toe Unidentified + Body Lining Ridged + + Corinthian Rim Unidentified + flat-top triangular Rim Sealant? + + Greek Body Lining + + Greek Body Lining Graeco-Italic? Body Lining + + Greek Body Lining + Greek Body Lining Greek Body Lining Greek Body Lining + + Toe Unidentified Late Punic + Toe Unidentified Byzantine + Corinthian Rim Sealant? +


IR Result Isopropyl No organic materials Isopropyl No organic materials No organic materials Isopropyl Isopropyl Isopropyl Isopropyl Isopropyl Isopropyl Isopropyl No organic materials Isopropyl Isopropyl Isopropyl Isopropyl Isopropyl Unidentifiable Isopropyl Isopropyl Isopropyl Unidentifiable Isopropyl Isopropyl Isopropyl Isopropyl Isopropyl Isopropyl Isopropyl Isopropyl

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tane-toluene-diethyl ether (1:1:1). The separated components were made visible by spraying the plates with 20% sulfuric acid and heating to 100 °C on a hotplate for 15 s. Partial charring of the organic acids on the plate provided an additional basis for identification; abietic acid spots turn reddish-brown, whereas dehydroabietic acid spots turn yellow-brown to greenish-brown. G C Analysis. Samples for G C were prepared by extracting the crude sample with ether, extracting the ether solution (15 mL) three times with 5 m L of 5% sodium bicarbonate, acidifying the extract to p H 2 with concentrated hydrochloric acid, extracting the acids again with ether, drying the ether solution over anhydrous sodium sulfate, and methylating the acids with diazomethane. Both ether solutions were evaporated to dryness to determine the weights of organic materials and and acids in the sample. Gas chromatograms were obtained by using a Hewlett-Packard model 5880A gas chromatograph equipped with flame-ionization detector and a data station. The chromatographic analyses were isothermal at 200 °C on a 12-m-length cross-linked methyl silicone capillary column. The quantitative data in Table II are derived from these analyses. Peak identities were confirmed on a Hewlett-Packard model 5995C/ 96A G C - M S system with model 5997A workstation with a 15-m-length RSL-150 polydimethylsiloxane capillary column at an initial temperature of 100 °C rising at 5 °C/min to 250 °C. Reference Standards. Reference standards for T L C , G C , and M S were ob tained as follows. Pure abietic acid (mp 172-173 °C) was used as received. Dehy droabietic acid was prepared by oxidation of abietic acid with selenium dioxide to hydroxyabietic acid and subsequent dehydration with glacial acetic acid (II). 7Ketodehydroabietic acid was prepared by oxidation of dehydroabietic acid with po tassium permanganate and isolation of the product by way of the Girard reagent Τ (12). Pyroabietic acid (a mixture of dehydro- and dihydroabietic acids) was prepared by heating abietic acid with 10% palladium on charcoal to 250 °C for 1 h (13). Additional experimental details and analytical data are reported elsewhere by Smart (14).

Results and Discussion I R Spectroscopy. I R spectroscopy is a s i m p l e a n d r a p i d m e t h o d of i d e n t i f y i n g f u n c t i o n a l groups a n d skeletal types i n m i l l i g r a m samples of s o l i d organic materials. D i s p e r s i v e spectra have b e e n u s e d to d e t e r m i n e the

Table II.Analyses by Gas Chromatography-Mass Spectrometry Acids Samph Number 1 7 10 12

Organic Materials 84.41 76.78 73.14 71.52

in Total Sample 28.05 13.46 3.16 5.78

in Organic Fraction 33.23 17.53 4.33 8.07

Abietic Acid 1.0 20.9 none none

Dehydroabietic Acid 7.8 51.8 10.5 12.4

7-Ketodehydroabietic Acid 10.4 2.9 22.0 22.9

NOTE: All values are percentages. Values for resin acids are given as percentages of the acid fraction.


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provenance of fossil resins (15) a n d to identify organic remains i n pottery from Q u s e i r a l - Q a d i m i n U p p e r E g y p t as p i t c h rather than b i t u m e n (16). T h e h i g h resolution of F o u r i e r transform I R ( F T I R ) i n s t r u m e n t s p e r m i t s a m o r e d e t a i l e d study of skeletal absorptions a n d , thus, the identification of structures characteristic of w e l l - d e f i n e d botanical sources.


A b o u t 8 0 % of the d i t e r p e n e acids of the genus Pinus have an abietane skeleton, w i t h abietic a c i d (structure 3) as the p r e d o m i n a n t c o m p o n e n t . O t h e r d i t e r p e n e acids have a p i m a r a n e skeleton (structure 4). A l l c o m p o u n d s w i t h the abietane skeleton are d i s t i n g u i s h e d b y the presence of an i s o p r o p y l group. E x t e n s i v e theoretical a n d e m p i r i c a l w o r k (17) has s h o w n that the isop r o p y l group is identifiable b y (1) split s y m m e t r i c a l c a r b o n - h y d r o g e n d e formations at 1382.5 ± 2 . 5 a n d 1367.5 ± 2 . 5 c m " a n d (2) b y two skeletal vibrations. O n e of these vibrations occurs at a r e m a r k a b l y constant frequency of 1168.5 ± 1 . 5 c m , whereas the frequency of the other v i b r a t i o n decreases as a f u n c t i o n of the m o l e c u l a r w e i g h t ( M W ) of the rest of the m o l e c u l e , f r o m 1170 c m for M W 15 ( m e t h y l group) to 1142 c m " for M W 99 (heptyl group). F o r an attached m o i e t y of M W 259, as i n abietic a c i d , the b a n d w h o s e frequency d e p e n d s o n the m o l e c u l a r w e i g h t of the rest of the m o l e c u l e is found at still l o w e r w a v e n u m b e r s . O n aging, a n d m o r e r a p i d l y o n heating, abietic a c i d is o x i d i z e d first b y disproportionation (i.e., w i t h o u t n e e d of oxygen) to d e h y d r o a b i e t i c a c i d (structure 1) a n d t h e n (but o n l y i f exposed to oxygen) to 7-ketodehydroabietic acid (structure 2). T h e skeletal frequencies of d e h y d r o a b i e t i c a c i d l i e at 1110, 1130, a n d 1175 c m " (14). O f the 31 C a r t h a g i n i a n samples, 25 y i e l d e d I R spectra that indicate an i s o p r o p y l group (Table I), as illustrated b y the s p e c t r u m of C a r t h a g e sample 6 of the l i n i n g of a 6 t h - c e n t u r y A . D . B y z a n t i n e a m p h o r a ( F i g u r e l a ) . T h e c a r b o n - h y d r o g e n deformation bands lie at 1385 and 1367 c m ( F i g u r e l b ) , a n d the skeletal absorptions are at 1107, 1127, a n d 1175 cm" ( F i g u r e l e ) , a v e r y nearly perfect m a t c h for d e h y d r o a b i e t i c acid. Six s a m ples (2, 4, 5, 13, 19, a n d 23) y i e l d e d I R spectra that i n d i c a t e d either no organic constituents (samples 2, 4, 5, a n d 13) or a l o w concentration of 1

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Figure 1. IR spectrum of an amphora lining (sample 6): complete spectrum (a) and partial spectra (b and c) showing isopropyl group absorptions. unidentifiable organic c o m p o u n d s (samples 19 a n d 23). T L C later c o n f i r m e d the absence of b o t h abietic a n d d e h y d r o a b i e t i c acids for t h r e e of these six samples (5, 13, a n d 23). F o r the r e m a i n i n g three samples (2, 4, a n d 19), b o t h abietic a n d d e h y d r o a b i e t i c acids w e r e i d e n t i f i e d b y T L C although these c o m p o u n d s w e r e u n d e t e c t e d b y I R spectroscopy. E i g h t y p e r c e n t o f a l l the C a r t h a g i n i a n samples a n d 9 0 % of those that contain d i t e r p e n e resins detectable b y T L C w e r e i d e n t i f i e d as p i n e r e s i n derivatives b y a single I R s p e c t r u m . T h u s , I R spectroscopy is a useful r a p i d s c r e e n i n g t e c h n i q u e for large n u m b e r s of samples. H o w e v e r , its l i m i t a t i o n s are e v i d e n t . L o w concentrations of abietanes, i f present i n a strongly a b s o r b i n g matrix, may be undetectable or unidentifiable b y I R spectroscopy, a n d the l i m i t s of detectability d e p e n d o n the absorbance of the m a t r i x a n d cannot be categorically specified.


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T L C Analysis. S m a l l sample r e q u i r e m e n t s , m i n i m a l sample p r e p aration, h i g h sensitivity, a n d l o w cost make T L C an attractive m e t h o d for organic archaeometry. Its suitability for t h e detection o f r e s i n acids i n c o m p l e x mixtures was tested b y subjecting t h e C a r t h a g i n i a n samples to a t w o d i m e n s i o n a l t e c h n i q u e . E t h e r solutions o f the organic m a t e r i a l w e r e spotted onto t h e plate a n d first freed f r o m nonpolar components b y e l u t i o n i n one d i r e c t i o n w i t h heptane. T h e r e s i d u a l carboxylic acids w e r e t h e n d e v e l o p e d , w i t h reference standards i n adjacent tracks, i n the second d i r e c t i o n w i t h h e p t a n e - t o l u e n e - e t h e r (1:1:1). U n d e r these conditions, 7-ketodehydroabietic a c i d remains at or v e r y near the o r i g i n ( m a x i m u m retardation factor [Rf] = 0.04), b u t abietic a c i d a n d d e h y d r o a b i e t i c acid are r e a d i l y i d e n t i f i e d . T h e results o f T L C analysis are d i r e c t l y c o m p a r e d w i t h the I R results i n T a b l e I. O f t h e 31 C a r t h a g i n i a n samples, 26 c o n t a i n e d d e h y d r o a b i e t i c a c i d , b u t o n l y 12 o f these also c o n t a i n e d u n c h a n g e d abietic acid. T h i s finding is not s u r p r i s i n g , because abietic acid is c o n v e r t e d to d e h y d r o a b i e t i c acid as a f u n c t i o n o f t i m e a n d t e m p e r a t u r e . W e cannot d e t e r m i n e w h e t h e r the abietic acid was lost d u r i n g t h e manufacture o f the p i n e p i t c h o r d u r i n g its depositional history. L o s s d u r i n g d e p o s i t i o n is less l i k e l y , because almost a l l (six of seven) o f the most recent samples (from t h e B y z a n t i n e period) w e r e d e v o i d of abietic acid. O f the five samples that s h o w e d n e i t h e r o f t h e r e s i n acids b y T L C (samples 5, 13, 2 3 , 26, a n d 27), three ( 5 , 1 3 , a n d 23) y i e l d e d I R spectra that r e v e a l e d no i s o p r o p y l group. T h r e e samples (4, 26, a n d 27) d e m o n s t r a t e d the c o m p l e m e n t a r y rather than parallel functions o f I R a n d T L C analyses i n organic archaeometry. O r g a n i c materials w e r e not r e v e a l e d b y I R i n sample 4, b u t b o t h abietic a n d d e h y d r o a b i e t i c acids w e r e d e t e c t e d b y T L C i n the same sample. C l e a r l y , the r e s i n a c i d concentrations w e r e b e l o w t h e l i m i t o f detection o f w h o l e r e s i n I R spectroscopy b u t w e r e sufficient for detection b y T L C . C o n v e r s e l y , samples 26 a n d 2 7 showed n e i t h e r a c i d b y T L C b u t gave a clear i n d i c a t i o n of t h e i s o p r o p y l structure i n t h e I R spectra. I n this case, t h e I R t e c h n i q u e was superior; a l t h o u g h the r e s i n acids have b e e n lost e v i d e n t l y (most l i k e l y b y decarboxylation), the r e m a i n i n g n e u t r a l c o m p o u n d s r e t a i n e d t h e i s o p r o p y l g r o u p , a fact that a l l o w e d t h e identification of the samples as p i n e pitches. G C - M S Analysis. T h e acidic c o m p o n e n t s of four C a r t h a g i n i a n s a m ples (1, 7, 10, a n d 12) w e r e subjected to a c o m p l e t e analysis b y G C . S a m p l e p r e p a r a t i o n is d e s c r i b e d i n a previous section (see M a t e r i a l s a n d M e t h o d s ) . Results are g i v e n i n Table I I . T h e identities of t h e acids w e r e established b y (i) the r e t e n t i o n times o b t a i n e d f r o m reference samples, (ii) t h e c o m i gration of acids w i t h reference standards d u r i n g s p i k i n g e x p e r i m e n t s , a n d (iii) t h e mass spectra of the constituents (18). T h e organic content o f samples was consistently b e t w e e n 70 a n d 8 5 % of t h e total sample w e i g h t , b u t t h e acid fraction v a r i e d almost b y a n o r d e r of m a g n i t u d e , from 3 to 2 8 % o f t h e sample w e i g h t or from 4 to 3 3 % o f t h e


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organic fraction. T h i s v a r i a t i o n is p r o b a b l y d u e to differences i n i n i t i a l m e t h ods of p r e p a r a t i o n or, less l i k e l y , depositional history. T h e resin acids w i t h an abietane skeleton i n p i n e resins r e s p o n d to heat b y i s o m e r i z a t i o n to abietic a c i d , d i s p r o p o r t i o n a t i o n to d e h y d r o a b i e t i c a c i d , a n d oxidation to 7-ketodeh y d r o a b i e t i c . I n a d d i t i o n , t h e y are decarboxylated, a process that is catalyzed b y active clay (13) a n d alkaline conditions (19). T h e variations i n the acid c o m p o s i t i o n o f the four samples m u s t reflect differences i n p r e p a r a t i o n or history. S a m p l e 7 c o n t a i n e d m o r e than 2 0 % u n c h a n g e d abietic a c i d , m o r e t h a n 5 0 % d e h y d r o a b i e t i c a c i d , b u t v e r y little 7-ketodehydroabietic a c i d . T h i s c o m p o s i t i o n is not expected o f a p i n e p i t c h b u t of a p i n e r e s i n that has b e e n t h r o u g h slow d i s p r o p o r t i o n a t i o n i n an anaerobic e n v i r o n m e n t . T h i s r e s i d u e is therefore that of a p i n e r e s i n a d d e d to w i n e to make the retsina for w h i c h G r e e c e was n o t e d i n a n t i q u i t y as it is today. S a m p l e 1 c o n t a i n e d o n l y 1% u n c h a n g e d abietic a c i d , b u t m o r e than h a l f of the d e h y d r o a b i e t i c a c i d was o x i d i z e d to 7-ketodehydroabietic a c i d , a finding that indicates the presence o f air d u r i n g the p r e p a r a t i o n o f the p i t c h . Samples 10 a n d 12 are v i r t u a l l y i d e n t i c a l ; n e i t h e r c o n t a i n e d any u n c h a n g e d abietic a c i d , a n d b o t h c o n t a i n e d about twice as m u c h 7-ketod e h y d r o a b i e t i c a c i d as d e h y d r o a b i e t i c acid. B o t h are extensively decarboxy l a t e d , as i n d i c a t e d b y t h e i r l o w total acid content. Therefore, these samples are pitches that w e r e p r e p a r e d b y h e a t i n g a p i n e r e s i n for a l o n g t i m e or at a h i g h t e m p e r a t u r e w i t h ready access to oxygen, as w o u l d b e the case w i t h s t i r r i n g i n a shallow vessel. T h e G C data c o n f i r m e d the T L C results. T L C d e t e c t e d abietic a c i d i n sample 7 b u t not i n samples 1, 10, a n d 12. T h i s result indicates that a r e s i n acid concentration of 1% is b e l o w the l i m i t of detectability b y T L C . T L C r e v e a l e d d e h y d r o a b i e t i c a c i d i n a l l four samples, a n d this result was c o n firmed b y G C . T h e G C data also c o r r o b o r a t e d the u t i l i t y of I R spectroscopy. I R spectra s h o w e d the i s o p r o p y l structure i n a l l four samples, i n c l u d i n g those for w h i c h the a c i d fraction was less t h a n 1 0 % (samples 10 a n d 12). C l e a r l y , these i s o p r o p y l bands are not from the small a m o u n t o f r e s i d u a l acid b u t are caused b y skeletal absorptions of the i s o p r o p y l group i n decarboxylated n e u t r a l d e c o m p o s i t i o n products.

Conclusions T h e analytical methods a p p l i e d to the a m p h o r a shards from the h a r b o r of Carthage each have d i s t i n c t b u t o v e r l a p p i n g u t i l i t y . I R spectroscopy detects the carbon skeleton characteristic of p i n e r e s i n o r p i t c h w i t h a r e l i a b i l i t y of 8 0 - 9 0 % b u t w i t h o u t i d e n t i f y i n g i n d i v i d u a l constituents. It fails w i t h small amounts o f organic matter i n a strongly absorbing matrix b u t has the a d vantage of d e t e c t i n g the i s o p r o p y l group i n extensively decarboxylated s a m ples. Because of the speed a n d ease of I R spectroscopy, it is an effective


20.

B E C K ET AL.

Mediterranean

Transport

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s c r e e n i n g m e t h o d w h e n h u n d r e d s , or e v e n thousands, of c e r a m i c finds m u s t be tested. T L C is m o r e sensitive than I R spectroscopy i n detecting s m a l l amounts of r e s i n acids because it is a separation t e c h n i q u e , b u t it cannot identify p i n e resins that have b e e n c o m p l e t e l y decarboxylated. H o w e v e r , c o m p l e t e l y d e carboxylated resins are rare (two of 31 samples i n the present study), a n d T L C can be used also for the r a p i d a n d inexpensive s c r e e n i n g of large n u m b e r s of specimens w i t h a r e l i a b i l i t y of > 9 0 % . B o t h I R spectroscopy a n d T L C are therefore appropriate for d e t e r m i n i n g w h e t h e r an organic residue or l i n i n g is pinaceous. T h i s i n f o r m a t i o n is far from t r i v i a l because it l i m i t s the materials that a transport a m p h o r a m u s t have contained. O i l s dissolve p i n e p i t c h a n d are d i s c o l o r e d b y i t ; a transport a m p h o r a l i n e d w i t h p i n e p i t c h cannot have b e e n used to ship olive o i l b u t may have c o n t a i n e d w i n e , fruit, or p r e s e r v e d fish. G C (with or w i t h o u t identification of constituents b y M S ) remains the most precise, quantitative m e t h o d for the d e t a i l e d analysis of resinous r e mains a n d the choice w h e n a r e l a t i v e l y s m a l l n u m b e r of samples m u s t be s t u d i e d i n d e p t h . It provides information about the m e t h o d of p r e p a r a t i o n , that is, about early r e s i n a n d p i t c h technology. T h e analyses r e p o r t e d i n this chapter a n d elsewhere (20) have b e e n the i m p e t u s for c u r r e n t w o r k i n this laboratory o n r e p l i c a t i o n of ancient p i t c h m a n u f a c t u r i n g methods a n d i d e n tification of the types of p i n e resins that w e r e u s e d .

Acknowledgments W e thank T h o m a s F. Sanderson, H e r c u l e s Research C e n t e r , W i l m i n g t o n , D E , for a sample of p u r e abietic a c i d a n d Roxanne J . F i n e , Vassar C o l l e g e , for the preparation of the other standards. T h i s w o r k was s u p p o r t e d b y an e q u i p m e n t grant towards the a c q u i s i t i o n of an F T I R spectrophotometer from the N a t i o n a l Science F o u n d a t i o n ( D i v i s i o n of A n t h r o p o l o g y ; grant no. 84-01207). W e are grateful to Vassar C o l l e g e for its c o n t i n u i n g support of the A m b e r Research L a b o r a t o r y ( A R L ) ; this report constitutes A R L C o n t r i b u t i o n N o . 72.

References 1. Pliny Historia Naturalis, XVL:xvi-xxiii; Rackham, H., Ed.; Loeb Classical Li brary, Harvard University: Cambridge, 1968; pp 413-427. 2. Forbes, R. J. Studies in Ancient Technology, 3rd ed.; Brill: Leiden, 1964; Vol. I; pp 1-124. 3. Hanson, W. E. Bituminous Materials: Asphalts, Tars and Pitches; A. J. Hoiberg, Ed.; Wiley: New York, 1964; pp 1-24. 4. Tomkeieff, S. I. Coals and Bitumens; Pergamon: London, 1954; p 27. 5. Abraham, H. Asphalts and Allied Substances, 6th ed.; Van Nostrand: New York, 1960; Vol. I; p 54.



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6. Marschner, R. F.; Wright, H. T. In Archaeological Chemistry II; Carter, G . F., E d . ; Advances in Chemistry 171; American Chemical Society: Washington, D C , 1978; pp 150-171. 7. Mills, J . S., White, R. Stud. Conserv. 1977, 22, 12-31. 8. Condamin, J.; Formenti, F. Figlina 1976, 1, 143-158. 9. Shackley, M. J. Archaeol. Sci. 1982, 9, 305-306. 10. Wolff, S. R. Cahiers des Études Anciennes 1986, 19, 136-153. 11. Fieser, L . F.; Campbell, W. P. J. Am. Chem. Soc. 1938, 60, 159-170. 12. Pratt, Y. T. J. Am. Chem. Soc. 1951, 73, 3803-3807. 13. Fleck, E . E.; Palkin, S. J . J. Am. Chem. Soc. 1937, 59, 1593-1595. 14. Smart, C. J., B.A. Thesis, Vassar College, Poughkeepsie, NY, 1983. 15. Beck, C. W. Appl. Spectr. Rev. 1986, 22, 57-110. 16. Beck, C. W.; Moray, L . In Quseir al-Qadim 1978: Preliminary Report; W h i t comb, D . S.; Johnson, J. H., E d s . ; American Research Center in Egypt: Cairo, 1979; pp 253-256. 17. Bellamy, L. J. The Infrared Spectra of Complex Molecules; Wiley: New York, 1975; pp 21-29. 18. Zinkel, D . F.; Zank, L . C.; Weselowski, M . F. Diterpene Resin Acids, U . S . Department of Agriculture, Forest Service, Forest Products Laboratory: M a d ison, W I 1971. 19. Belov, V. N.; Kustova, S. D . J. Gen. Chem. USSR 1954, 24, 1083-1088. 20. Beck, C. W.; Ossenkop, D . J . In M. Katzev, The Kyrenia Wreck, in press. RECEIVED for review June 11, 1987. ACCEPTED revised manuscript March 7, 1988.


Archaeological Chemistry IV - American Chemical Society

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