Fluorescence Characteristics and PARAFAC Modeling of ... · Fluorescence Characteristics and...

Fluorescence Characteristics and PARAFAC Modeling of

Bitumen from Ancient Ceramics

Morgan Bida1, David Meiggs2, Christine Kim3, Cody Cummings3 and Todd Pagano1

1. Laboratory Science and Technology Program, Department of Science and

Mathematics, National Technical institute for the Deaf/Rochester Institute of

Technology, Rochester, New York, USA (Email: [email protected]; [email protected]) 2. Department of Sociology and Anthropology, College of Liberal Arts, Rochester

Institute of Technology, Rochester, New York, USA (Email: [email protected]) 3. Chemistry Program, College of Science, Rochester Institute of Technology,

Rochester, New York, USA (Email: [email protected]; [email protected])

Received: 14 August 2017; Revised: 20 September 2017; Accepted: 02 November 2017

Heritage: Journal of Multidisciplinary Studies in Archaeology 5 (2017): 69‐83

Abstract: Bitumen is often found at archaeological sites around the world due to its prevalent use in

antiquity. While archaeologists have identified bitumen source areas using geochemical and isotopic

characterization, methods for measuring the absorbance and fluorescent properties of bitumen are not

often employed in archaeology despite their relatively low‐cost and the minimally destructive nature of

these methods. To examine the use of fluorescent techniques to characterize bitumen, we extracted

residues found on ancient ceramics from Vizhinjam, India and examined their absorbance and

multidimensional fluorescence profiles. We then de‐convoluted the fluorescence excitation‐emission

matrices (EEMs) using parallel factor analysis (PARAFAC). Our absorbance results showed profiles

similar to those for crude oils and bitumen. Fluorescence EEMs indicated a broad fluorescence profile

with peak emissions occurring in the area of 400 – 500 nm at an excitation wavelength of 280 nm.

PARAFAC modeling suggested a 3‐component model to describe the contributing fluorophores in the

ancient bitumen and we have suggested a possible maltene‐like component (C1), and two asphaltene‐like

components (C2 and C3). The comparison of samples by their PARAFAC loading scores may indicate

two source areas for bituminous sealants in the foreign ceramics at Vizhinjam. These variations in

fluorescence can be useful toward a greater cultural understanding of ancient bitumen samples.

Keywords: Multidimensional Fluorescence Spectroscopy, Parallel Factor Analysis,

Absorption Spectroscopy, Ancient Bitumen, Vizhinjam, Mesopotamia, Egypt

Introduction Bitumen, oils, and tars have been used for a variety of applications by humans for

millennia, and they are found in archeological sites around the world (e.g., Connan,

1999; Stacey, 2013). Bitumen specifically has been used for a wide variety of purposes,

such as: a hafting adhesive; a sealant for jars, containers, palm roofs, boats, and coffins;

and as a mortar additive for dwellings, temples, and palaces (Stacey, 2013). Previous

ISSN 2347 – 5463 Heritage: Journal of Multidisciplinary Studies in Archaeology 5: 2017

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research has identified source areas for archaeological bitumen, illuminating patterns

of resource use and exchange networks (Connan, 1999; Connan et al., 2006; Kato et al.

2008; Schwartz and Hollander, 2008). The aim of this pilot study was to ascertain if

bitumen sealants in ceramic vessels presumably used in long‐distance trade could be

characterized by a relatively inexpensive, accessible technique. To this end, we

analyzed solvent extracts of bitumen‐coated ceramics from the site of Vizhinjam

(Kerala, India) using ultra‐violet/visible (UV‐Vis) absorbance and fluorescence

spectroscopy, combined with parallel factor analysis (PARAFAC) to identify patterns

in the spectroscopic data. The absorbance and fluorescence properties of the aromatic

fractions of bitumen, coal, and oil have been extensively studied in the fuel and energy

industry (Ryder, 2005). Multidimensional fluorescence with PARAFAC may have

utility in determining the origin of the bitumen used on ceramics in antiquity, or the

processes by which the bitumen was treated, both areas that can augment the cultural

understanding of these artifacts. To the best of our knowledge, this is the first

application of multidimensional fluorescence to bitumen samples in archaeology. Our

results demonstrate use of the technique to characterize ancient bitumen, and indicate

potential for further application.

We examined series of ceramic sherds with possible bitumen residues excavated from

Vizhinjam (Kerala, India). These sherds appear to conform to known trade ware types

(e.g., so‐called torpedo jars)—with possible origins in Southwest Asia—which have

been excavated from other sites along the west coast of India (Gupta et al., 2001). But

possible diversity in the originating point of shipments, and how these might have

varied geographically on the west Indian coast and through time, are presently

unclear. Today, Vizhinjam is a small fishing village and part of a natural harbor in

India. In ancient times, Vizhinjam was an important seaport, and ruled by the Ay

dynasty from about 500 – 600 AD (Kumar et al., 2013). It supported trade and activities

such as pearl fishing. The harbor is still used for trading, evolving to become an

international trade port.

Background The earliest evidence for the use of bitumen in Southwest Asia dates from the

Mousterian period (ca. 70,000 BP; Boëda et al., 2008; Hauck et al., 2013). Deposits across

greater Mesopotamia, Egypt, and the Arabian Peninsula were exploited during all

cultural periods in this area (Boëda et al., 2008; Connan and Van de Velde, 2010).

Bitumen was a common sealant for porous ceramic fabrics in antiquity, reducing

leakage of transported liquids, increasing preservation, and providing better

transportability for a variety of valuable substances. In an effort to understand patterns

in areas of resource exploitation and exchange practices of bitumen, archaeologists

have used a variety of methods, including gas chromatography and isotopic analysis,

to identify bitumen source localities in Southwest Asia (e.g. Barakat et al., 2005;

Connan et al., 2005, 2006; Schwartz and Hollander, 2008). Methods applied in previous

research, however, require instruments for which access is generally limited, and the

protocols are complex and time‐consuming. Multidimensional fluorescence

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spectroscopy, alternatively, is a relatively simple and rapid technique whose results

have been used to “fingerprint” of a variety of substances (e.g., Bida et al. 2015;

Callejón et al. 2012; Eaton et al. 2012; Hall et al 2005; Pagano et al. 2012; Sirkorska et al.

2004). The low cost of data collection and minimally destructive sampling make its

potential in archaeology appealing.

Bitumen is a complex substance with properties that can vary depending on source,

added chemicals or materials, and physical treatments (Handle et al., 2014). To analyze

its composition, it is common to separate bitumen into fractions with similar chemical

properties, including saturated hydrocarbons, aromatics, resins, and asphaltenes

(Handle et al., 2014; Merino‐Garcia et al., 2010). Asphaltenes are a sub‐set of the

aromatic fraction, but are typically distinguished as the portion that is insoluble in n‐

heptane (a non‐polar solvent), yet soluble in toluene (a slightly polar solvent).

Maltenes, also part of the aromatic fraction, are soluble in n‐heptane and hexanes with

some solubility in toluene (Handle et al., 2014). Bitumen, in general, is a mixture of

compounds and should not be considered a purely aromatic substance. But it is the

presence of a wide variety of large aromatic compounds in bitumen—composed of

highly stable planar or cyclic regions—that is responsible for its fluorescence.

It is for this reason that fluorescence spectroscopy can be used to qualitatively analyze

ancient bitumen samples. By systematically varying the excitation and emission

wavelengths to create a multidimensional matrix of fluorescence data (called an

excitation‐emission matrix; EEM), researchers can obtain a “fingerprint” of the

fluorescence‐producing constituents in the ancient bitumen, similar to analyses

previously performed in crude oil (Ghatee et al., 2012). An EEM represents a

combination of all fluorescing components in a given sample, preventing detailed

comparison of possibly subtle differences between samples. Application of a

chemometric technique to multidimensional fluorescence results, such as parallel factor

analysis (PARAFAC), allows data to be de‐convoluted into spectra of coexisting

fluorophores in the bitumen EEMs. PARAFAC is a statistical technique that fits

multiple two‐way arrays to three‐dimensional data (Harshman and Lundy, 1994).

Multidimensional fluorescence with PARAFAC analysis has been extensively used to

analyze natural organic matter in water (Bida et al., 2015; McKnight et al., 2001; Pagano

et al., 2012; Stedmon et al., 2003). Algorithms used in PARAFAC decompose EEMs into

excitation and emission spectra and loading scores for each sample EEM (Andersen

and Bro, 2003). Loading scores correlate to the abundance of the individual

fluorophores or groups of similarly fluorescing compounds present in each EEM, and

augment the ability to resolve multidimensional fluorescence data (Andersen and Bro,

2003). However, due to the heterogeneous complexity of bitumen and similar

petroleum derivatives, samples of this nature may be subject to confounding photo‐

physical phenomena (e.g., internal conversion, intersystem crossing, fluorescence

energy transfer) that have the possibility to violate the strict multilinear assumptions of

PARAFAC (Ghatee et al., 2012; Strausz et al., 2009). Little is known concerning the

application of multidimensional analysis with PARAFAC to ancient bitumen, so


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understanding of the effects of various photo‐physical phenomenon on the modeling

of these types of samples is limited and remains to be fully described.

In this study, we recorded UV‐Vis absorbance profiles for extracted ancient samples

and a modern bitumen reference. We then studied their fluorescence properties,

examining the multidimensional fluorescence of bitumen. The resulting 3‐dimensional

EEMs were used to perform PARAFAC in order to de‐convolute the EEMs into spectra

of fluorophores, or groups of similarly fluorescing compounds. This approach allowed

for the derivation of information about the general groups of fluorophores present in

bitumen and to assess the extent to which the fluorescence from each contributing

group of fluorophores (in the case of the PARAFAC analysis, referred to as

‘components’) was present in each sample. Unfortunately, it was not possible to obtain

bitumen from known sources in the broad region (Mesopotamia‐Egypt‐Arabia)

representing a likely origin of the pottery we investigated. Therefore, while we were

able to compare our results with a known bitumen reference and with literature data,

we are not able to posit sources in Southwest Asia for ancient bitumen we identified.

Site Description and Excavation Information

Vizhinjam is located in South Kerala, India, and occupies a significant position in the

history of the region due to its natural harbor. Its strategic location along ancient

Indian Ocean trade routes made it a desirable and contested possession of the Ay

Dynasty (3rd cent. BC – 8th cent. AD) and their competitors. Trade with the Roman

Empire in the early centuries AD is attested at other places along the west coast of

India (Gupta et al., 2001), and the quality of the harbor at the site may have been noted

in a 1st century AD Greek sea guide (Periplus of the Erythrean Sea, Kumar et al., 2013).

Vizhinjam became a center of learning, trade, and commerce. Starting in the 7th

century AD, the Ay shifted their capital to Vizhinjam, and perhaps in the 8th century

AD, constructed a fort to defend it(Kumar, 2006a, 2006b, Rajesh and Kumar, 2010a,

2010b). Archaeological excavation at the site from 2011‐2013 aimed to illuminate its

early history and trade networks. Pottery found from the earliest levels (2nd cent. BC –

2nd cent. AD) indicate exchange within a wide network from Bengal to West Asia

(Kumar et al., 2015). In particular, these levels contained sherds of amphorae and so‐

called torpedo jars (Kumar et al., 2015). These types are thought to originate in the

greater region that includes Mesopotamia and the Persian Gulf littoral zone, as well as

communities near the Red Sea. The sherds examined in this study come from these

layers. Thirty sherds identified as amphora or torpedo jars were selected at the

University of Kerala that displayed evidence of black residues on their interior

surfaces.

Methods Sample Preparation Sherd surfaces were carefully scraped with a surgical scalpel to remove areas of visible

adhering residue. The resulting powders, a mixture of ceramic fabric and residue, were

then placed in vials labeled VZM1‐30. Each of these samples was dissolved in toluene

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by adding 12.5 mg of powder to 25 mL a volumetric flask that was half‐filled with

solvent. Samples were protected from light degradation by covering them in foil. Each

sample was sonicated for 10 minutes to break up any aggregated material and to

separate bitumen from the ceramic matrix. The sample flasks were then placed on a

wrist shaker, mixing vigorously for 10 minutes, and then mixed more slowly on an

orbital shaker for 24 hours. After mixing, they were brought to volume with toluene

and inverted in triplicate to ensure thorough mixing. Each sample was then passed

through a 0.22 μm nylon filter to collect suspended ceramic and insoluble components.

The filtered toluene solution was collected and diluted such that its absorbance was

below 1.0 absorbance units at 280 nm. The absorbance profile and EEM of each sample

was then collected on the diluted samples. The nylon filter papers were dried via

evaporation and weighed to determine the mass of non‐dissolved components in the

samples in order to infer the proportion of bitumen dissolved from the original sample

weight. Fluorescence PARAFAC results for each sample were normalized by their

corresponding bitumen fraction weights to compensate for differences in extracted

concentrations.

Instrumentation Parameters

A Perkin Elmer Lambda 650 spectrophotometer was used to record the absorbance

profile for each sample from 280 – 600 nm at 1 nm increments using a resolution of 5

nm. A Varian Cary Eclipse spectrofluorometer was used to collect EEMs for each

sample. Samples were excited from 280 – 600 nm in 5 nm increments using a 5 nm slit

width. The resulting emission was recorded from 295 – 600 nm at 1 nm intervals using

a 5 nm slit width. Fluorescence data were corrected for primary and secondary inner

filtering based on the algorithms proposed by MacDonald et al. (1997) and also for

absorbance of the cuvette wall and reflectance losses at the air:wall and wall: solvent

interfaces. All corrections were performed using an in‐house MATLAB program (Hall

et al., 2005). PARAFAC models were created using the PLS Toolbox (Eigenvector

Research, 2012) in Matlab (Mathworks Inc., 2014).

Results One of our goals was to confirm the presence of bitumen on the ceramic samples by

matching absorbance profiles to those of the literature. A total of 30 samples were

analyzed for absorbance and only 16 of them showed matching absorbance profiles.

The remaining 14 appeared to be absent of bitumen or other molecules capable of

absorbing light when dissolved in toluene. Absorbance spectra for the 16 samples

(Figure 1) were similar to those in the literature for bitumen and asphaltenes,

characterized by a maximum absorbance around 280 – 290 nm (Strausz et al., 2009;

Zhang et al., 2014). This suggested the presence of bitumen in many of our samples.

However, the magnitude of the absorbance cannot necessarily be considered to be

proportional to the concentration of bitumen due to possible interactions occurring

within the molecular complexity of bitumen. For example, Strausz et al. (2009) reported

increasing absorbance in higher molecular‐weight fractions and suggested this could


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be due to both an increase in the number of aromatic carbons as well as the size of the

aromatic chromophore, independent of concentration. Further, the absorbance spectra

shown in Figure 1 cannot necessarily be compared quantitatively, as each sample had

varying amounts of bitumen extracted from the initial sample weights (which also

contained varying amounts of ceramic and other components).

Figure 1: Absorbance profiles for 16 bitumen‐containing samples in toluene. The

maximum absorbance for each sample appear in the range of 280‐300 nm, which

matches similar samples from the literature (Strausz et al., 2009; Zhang et al., 2014).

Absorbance readings below 280 nm were not recorded because this is the area in

which toluene absorbs and interferes with the sample.

Fluorescence EEMs (see examples in Figure 3) showed varying intensities across broad

fluorescence profiles with peak emissions occurring in the area of 375 – 600 nm at

excitation wavelengths from 280 – 450 nm. Of the 30 samples tested, only 16 showed

fluorescence emission spectra with high signal‐to‐noise (S/N) ratios. Data from these

samples were subjected to removal of Rayleigh and Raman scatter and corrections for

inner‐filtering, and a 3‐component PARAFAC model was generated (Figure 2). The 3‐

component model was validated according to the procedure described by Stedmon

and Bro (2008), which included a) visual inspections of each component in 2, 3, and 4‐

component PARAFAC models, b) comparison of sum of squared errors between

models, and c) analysis of residuals EEMs. The remaining 14 samples showed little

fluorescence signal and low S/N, so were excluded from the dataset prior to inner‐filter

correction and PARAFAC modeling. Low fluorescence in these samples may be due to

several possible factors. It may indicate a low proportion of bitumen relative to sample

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mass in this group. It also could be that a plant‐derived resin (e.g., pine tar) or wax was

used as a sealant in these vessels rather than bitumen. Naturally‐derived waxes are not

aromatic compounds, and plant resins have much smaller aromatic molecules than

bitumen (Egenberg et al. 2002) that, if they fluoresce at all, will have dramatically

different signatures. These compounds might be identified by infrared spectroscopy

(e.g., Beck et al. 1989). It is also possible that there were no residues in these samples,

and the staining on the pottery resulted from other factors.

Figure 2: Three‐component PARAFAC model generated from 16 bitumen‐containing

samples in toluene, showing modeled EEM contour plots (left) and excitation and

emission loading spectra (right) for each component (C1‐C3).


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Table 1: Three‐component PARAFAC Model Excitation and

Emission Spectral Summary

Comp EX max (nm) EX Range EM Max (nm)

1 330 (485) < 280 ‐ 580 595

2 300 < 280 ‐ 435 434

3 415 (320) < 280 ‐ 505 478

Table 2: Fluorescence Data from Literature Studies on Asphaltenes, Maltenes

and Whole Bitumen

EX Range

(nm)

EM maxima

(nm) Detection Method Comments

<300 ‐ >400 420, 440, 450 Multidimensional Fluorescence

(Ghatee et al., 2012)

Crude oil

asphaltenes

310 ‐ 335 440, 450 Fluorescence

(Zhang et al., 2014)

Asphaltenes

from bitumen

488 540 (600) Multidimensional Fluorescence

(Handle et al., 2014)

Crude oil

maltenes

365 420 Fluorescence

(Groenzin and Mullins, 2000)

Asphaltenes

from coal

365 470, 500 Fluorescence

(Groenzin and Mullins, 2000)

Crude

oilasphaltenes

350 480 Fluorescence(Strausz et al., 2009) Crude oil

asphaltenes

In the 3‐component PARAFAC model, Component 1 (C1) showed emission between

500‐600 nm with a maximum at 595 nm. Component 2 (C2) showed emissions between

330‐500 nm and an emission maximum at 434 nm. Component 3 (C3) showed

emissions between 400‐500 nm with an emission maximum at 478 nm. When

comparing our 3‐component PARAFAC model and fluorescence spectra (Figure 2,

Table 1) with data in the literature, we noticed similarities in the emission maxima and

shape of the emission and excitation curves for all three components (Table 2).

Component C1 had an emission maximum of 595 nm and is similar to the 540 – 580 nm

emission maxima for maltenes reported by Handle et al. (2014), who subjected their

samples to a rigorous fractionation and preparation. Morgan et al. (2010), however,

reported emission maxima in the range of about 420 – 500 nm for maltenes from crude

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oil dissolved in n‐heptane. Therefore, additional research using n‐heptane or hexanes

to dissolve the bitumen samples is needed to confirm a maltenes designation for

component C1 and to obtain more robust emission spectra for this fraction. Maltenes

are reported to be only slightly soluble in the toluene solvent used in this study, but the

heterogeneous nature of the maltene designation lends support to the solubility of

certain fractions within the mixture in toluene. For the purposes of this study,

component C1 was characterized as maltene‐like, pending additional investigation.

Component C2 had a 434 nm emission maximum that is similar to asphaltenes

precipitated from crude oil using pentene in a 90‐degree optical cell arrangement

(Zhang et al., 2014). Emission maxima from 420 – 450 nm were also reported for

asphaltenes extracted from crude oil in toluene using multidimensional fluorescence

spectroscopy with 90‐degree optical alignment, matching our methods (Ghatee et al.,

2012).Component C3, with an emission maxima of 478 nm, seems to match asphaltenes

precipitated from California crude oil and then dissolved in toluene using a 90‐degree

optical orientation (Groenzin and Mullins, 2000). Therefore, for the purposes of our

study, we attributed components C2 and C3 both a designation of asphaltene‐like,

indicating that both may contain fluorophores similar to that reported in the literature

for asphaltenes. Clearly additional research using methods to further fractionate

samples is needed, however in this study, such rigorous sample preparation was not

practical due to the limited amount of sample available at the time of research.

The PARAFAC model provides a loading score for each of the fluorescence EEMs

entered into the algorithm, which are indicative of the contribution of each component

to the total EEM for a particular sample. The loading scores for each sample were

normalized by sample weight to compensate for possible differences in extracted

concentration. In terms of the loading scores for our samples used in the PARAFAC

model, we found that components C1 and C2 showed the greatest variation between

samples, while component C3 remained relatively constant. Therefore, we examined

the loading scores for components C2 and C1 more closely to determine if the variation

between samples followed a pattern. Figure 3 shows component C2 versus component

C1 loading scores and clearly illustrates at least two main groups of fluorescing

samples. The group outlined in red has samples that are characterized by low scores

for components C1 and C2, and are generally blue‐shifted in their spectra compared to

the other groups. The group outlined by a dotted purple line shows that there are two

subgroups that have higher loadings for component C1 (potentially, maltene‐like).

Meanwhile, sample VZM16 appears to segregate itself with characteristic high loadings

for component C2 and intermediate loadings for component C1. These results were

supported by a hierarchical cluster analysis (Ward’s linkage) using all three

components (C1‐C3) that showed the same grouping as shown in Figure 3, but the

statistical significance of this result is difficult to evaluate. The loading scores from the

PARAFAC model clearly show some separation between at least two distinct groups or

types of samples with additional subgroup separation possible, but the nature of this

separation is unknown. These results may hold significance in terms of the origin of


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the bitumen samples and the preparation processes applied to the bitumen by ancient

cultures (e.g., heating, mixing, and dilution). Nonetheless, either of these possible

explanations will add to the cultural understanding of these samples and may be a

worthwhile avenue for additional investigation. An expanded sample dataset,

including reference material from potential source areas, combined with other forms of

sample preparation could add more robustness to the PARAFAC models and support

a more complete understanding of these results. Given the limited use of fluorescence

spectroscopy and PARAFAC to analyze ancient bitumen, we believe our results

represent a promising first‐step toward progressing the use of this technique in

archaeology.

Figure 3: PARAFAC loading scores for Component 2 versus Component 1 (left) and

corrected EEMs from two select samples, VZM1 and VZM23. The loading scores

appear to group themselves into three categories indicated by a maroon line, an

orange line, and a dotted line. Within the grouping shown with the dotted line, two

subgroups appear to exist. The two corrected‐EEMs are shown to illustrate spectral

differences between the two groups, characterized by a more red‐shifted emission in

VZM1 compared to VZM23.

While the precise nature of the difference between the groups based on their

PARAFAC component scores is not fully defined, it does represent a significant

chemical difference that may indicate two source areas for the bitumen extracted from

the Vizhinjam trade wares. No known sources of bitumen exist in India. Trade

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connections between South Asia and Southwest Asia are documented since at least the

Harappan period, but more pertinent is continued evidence of trade routes between

the Red Sea and Persian Gulf in the early 1st millennium AD (Seland, 2011; Tomber,

2007). These two areas may have represented different economic spheres of trade, one

Roman and the other Mesopotamian, respectively. Both areas possess sources of

bitumen utilized in antiquity and identified geochemically on artifacts (Barakat et al.,

2005; Connan et al., 2006; Schwartz and Hollander, 2008). Additionally, trade wares

excavated from Anuradhapura, Sri Lanka (mid‐1st millennium AD) were sealed with

bituminous sealants likely sourced in Luristan, western Iran (Stern et al., 2008). So, the

two potential groups of bitumen identified in this analysis could tentatively represent

source areas within or between Roman trade networks through the Red Sea and

Mesopotamian sources, obtained through the Persian Gulf. This would be particularly

significant if the groups corresponded with different ceramic types associated with

these two regions, i.e., amphorae and torpedo jars. Due to the lack of sample from

regional bitumen sources in this study, it is not possible at present to make any

conjecture with respect to possible origins of the ceramics analyzed here.

Yet, given these promising results, next steps should involve multidimensional

fluorescence study of modern bitumen samples from known source areas in Southwest

Asia, as well as other sealants used in antiquity, such as pine or birch tars to

characterize any fluorescent behavior. In addition, various aspects of the technique

should be clarified, such as: the solubility of maltene components in various solvents,

identifying effects of possible confounding photo‐physical phenomena, and variation

of absorbance with concentration. These steps will establish a robust basis for further

application of the technique and an initial database with which to compare

archaeological results. Data from samples of ancient pottery from specific entrepôt that

used routes through the Red Sea and Persian Gulf will then help to establish patterns

in use of particular sources to delineate patterns in long‐distance exchange across the

Indian Ocean in the past. Additional samples from Vizhinjam and other contemporary

sites along the west coast of India will also augment our understanding of ancient

maritime trade.

Conclusion Toluene extractions from ancient ceramic samples found in Vizhinjam produced

absorbance and fluorescence results characteristic of bitumen and its fractions. The

bitumen EEMs produced a 3‐component PARAFAC model with possible comparisons

to literature studies of bitumen, crude oils, and their fractions. We suggested that

component C1 may be maltene‐like, while components C2 and C3may be asphaltene‐like.

Further, when samples are differentiated based on their scores of component C2

relative to component C1, different groupings of samples emerge. Future work will

focus on generating possible qualitative associations between the distribution of

component scores and geographic areas of origin. Further, we would like to extract the

samples in different solvents and more rigorous sample fractionation to generate

additional fluorescence spectra to build PARAFAC models. These results illustrate the


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first known use of PARAFAC to analyze multidimensional fluorescence spectra from

archaeological bitumen.

Acknowledgements The authors wish to express gratitude to the National Technical Institute for the Deaf

(NTID) Undergraduate Research Fund for the student grant award that helped to fund

laboratory equipment for this project. We particularly thank Dr. Rajesh S.V. for

providing the ceramic samples from Vizhinjam.

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