Bull. Natl. Mus. Nat. Sci., Ser. B, 40(3), pp. 101–106, August 22, 2014

Diatom Analysis of Cuneiform Tablets Housed in the British Museum
Akihiro Tuji1,*, Anke Marsh2, Mark Altaweel2, Chikako E. Watanabe3 and Jonathan Taylor4
1

Department of Botany, National Museum of Nature and Science,
Amakubo 4–1–1, Tsukuba, Ibaraki 305–0005, Japan
2
Institute of Archaeology, University College London,
Gordon Square 31–34, London WC1H 0PY, U. K.
3Osaka Gakuin University,
Kishibe-minami 2–36–1, Suita-shi, Osaka 564–8511, Japan
4
Department of the Middle East, The British Museum,Great Russell Street, London WC1B 3DG, U. K.
*E-mail: tuji@kahaku.go.jp(Received 21 May 2014; accepted 25 June 2014)

Abstract Clay and silt powders taken from Mesopotamian cuneiform tablets and their surface
were examined for biological indicators (speciﬁcally, diatoms). The tablets are dated to the Third
Dynasty of Ur and belong to the category of economic and administrative texts. Three diatom species, Nitzschia palea, Stephanodiscus minutulus and Discostella sp., were identiﬁed, though they
were found in quite low densities. These species are very common in polluted/eutrophic water.
Further studies are needed, however, to exclude the possibility that these diatoms are a result of
later contamination, for instance via the subsequent burial of the tablets.
Key words : conservation, cuneiform tablets, diatom, Mesopotamia.

Introduction
Diatoms are important proxies for palaeoenvironmental reconstruction in archaeological science (Battarbee, 1988; Juggins and Cameron,1999). For the last few years, we have been
studying diatoms in cuneiform tablets with theaim of reconstructing the palaeoenvironment ofancient southern Mesopotamia (Tuji et al., 2011).
In an earlier investigation in 2008 at the British Museum, we examined cuneiform tablets
using a metallurgical microscope. On the surfaceof 16 cuneiform tablets, many diatom-likeobjects, which seemed to be Nitzschia species
and centric diatoms, were seen. The tablets weredated to the Third Dynasty of Ur (Ur III Dynasty:
2112–2004 BC), and originated from the sites ofUmma and Girsu in southern Mesopotamia (Tujiet al., 2011). There were difﬁculties in identify-

ing diatom species with the metallurgical microscope because of low resolution and use of
reﬂective light. We realised that we needed to use
a biological (transparent) light microscope (LM)
and/or scanning electron microscope (SEM) to
identify diatoms; sampling from the cuneiform
tablets for diatom analysis was essential.
In 2012, we conducted a scientiﬁc analysis of
cuneiform tablets by inspecting tablet surfaces
with a metallurgical microscope and samplingmaterial from cuneiform tablets at the British
Museum under the supervision and permission
from Museum staff. In this paper, we report theresults of this scientiﬁc analysis and discuss theramiﬁcations of these results.

Akihiro Tuji et al.

102

Materials and Methods
Direct examination of diatoms and samplingfrom the cuneiform tablets housed in the British
Museum (BM).
At the British Museum on 12–14 March 2012,
we started our analysis by inspecting cuneiform
tablet surfaces using a metallurgical microscope(BXFM-S, Olympus, Tokyo) with a long working distance objective lens (LMPLFLN, Olympus, Tokyo) to search for diatoms. We examined
economic tablets, which were all written during
the Ur III period (2112–2004 BC), originatingfrom the sites of Umma and Girsu in southern
Mesopotamia. In particular, we looked closely at
any cracked surfaces, which might expose intact
internal clay and silt. This examination was a follow-up study to clarify the outcome of the earlier
investigation in August 2008, when diatom-likeremains were found on the surface of 16 Ummatablets. Our investigation started with the reexamination of those 16 tablets and was followed
by observations of a further 83 tablets.
In summary, we looked at a total of 99 tablets
under the microscope, and diatoms wereobserved on 33 of those tablets (Figs. 1–3). We
sought permission to take samples from eighttablets from those examined in 2008, six new
Girsu tablets and 18 new Umma tablets. In thecourse of seeking permission, we learned thatmany ʻﬁredʼ tablets were among those on which
diatoms had been observed, except BM 93202,
which was apparently not ﬁred for conservation.
Permission was eventually granted for seven outof eight 2008 tablets, four out of six Girsu tablets, and 12 out of 18 Umma tablets. Sampling
was carried out on 23 tablets in total under thesupervision of Museum staff on 16 March.
The samples from the tablets were prepared
and analysed at the National Museum of Natureand Science in Tsukuba, Japan, using the methods described below.
a. Direct observation using SEM
Clay and silt powders from six tablets werespread on carbon-coated double-sided adhesive
tape (Okenshoji Co., Ltd., Tokyo) on SEM stubFigs. 1–3. Diatoms observed on the surface of
cuneiform tablets under a microscope (Courtesyof the Trustees of the British Museum).

mounts. The stub mounts were sputter-coatedwith platinum and examined using a SEM (JSM6390 with LaB6 gun, JEOL, Tokyo).
b. Boiling water treatment of diatom frustules
About 5 mg of the clay and silt powders were
put into 50 ml disposable polypropylene centrifuge tubes (Watson Co., Ltd., Tokyo). About
10 ml of ﬁltered tap water was added to eachtube. The water was ﬁltered with polypropylene
ﬁlter cartridges with 5 µm and 0.5 µm openings

Diatom Analysis of Cuneiform Tablets(TCW-5N-PPS and TCW-05N-PPS, Advantec
Co., Ltd., Tokyo). This should have removed any
diatoms present in the tap water. Tap water wasused because distilled water can dissolve diatom
frustules. Each tube of disaggregated suspension
was heated in a microwave oven at 600 W for
5 minutes.
c. Acid treatment after boiling water treatment
After the boiling water treatment, 0.5 ml of 1.5
ml hydrochloric acid was added to each tube andthe tubes were left to stand overnight.
SEM examination of the treated material
3 ml of each sample of material that had undergone boiling water and acid treatment was ﬁltered using a membrane ﬁlter with 1.2 µm openings (RTTP02500, Merck Millipore). After
ﬁltering the treated material, the ﬁlters were
washed using 2.5 ml distilled water for a shorttime. The ﬁlters were cut into small pieces andattached to SEM stub mounts using carboncoated double-sided adhesive tape. The stub
mounts were sputter-coated with platinum andexamined using SEM.
Strong acid treatment of diatom frustules
About 5 mg of the clay and silt powders were
put into 15 ml glass centrifuge tubes. About 5mlof concentrated nitric acid, including 10% concentrated hydrochloric acid, was added to eachtube. These tubes were kept at room temperature
for ca. two hours to remove any calcium compounds. The tubes were then heated overnight ina water bath at 70 degrees Celsius. After the acidtreatment, the treated materials were washedthree times with ﬁltered tap water using a centrifuge. After the ﬁnal washing, the treated materials were kept in 70% ethanol. The disaggregatedsamples were then mounted in ZRAX (developedby W.P. Dailey) and examined by LM (normal
biological microscopy: Axiophoto, Zeiss, Jena).
Results
Since the diatom frustules in cuneiform tablets
were thought to be very fragile (Tuji et al., 2011),

103

we tried using mild treatment on samples fromthe cuneiform tablets as a ﬁrst choice. The ﬁrst
treatment to be applied to the samples was theboiling water treatment, but this resulted in no
diatoms being found. Because there was a possibility that the diatom frustules might have dissolved, direct observation using a SEM wasapplied to a sample of the clay and silt powders(no disaggregate treatment) from the tablets.
However, no diatoms were found using thismethod either. It was then determined that calcium compounds might be obscuring or covering
the diatoms. As such, the acid treatment wasapplied to the samples that had undergone theboiling water treatment to eliminate the calcium
compounds. These were then examined using theSEM. However, only the following three diatom
species were found:
Nitzschia palea (Kütz.) W.Sm.

(Figs. 5–7)

Tablet BM28109 (Fig. 4).
Length: 27 µm, breadth: 4.5 µm, striae 34/10 µm.

Stephanodiscus minutulus (Kütz.) Cleve et Möller
(Fig. 8)
Tablet BM104703.
Diameter: 4 µm.
Discostella Houk et Klee sp.
Tablet BM104703.
Diameter: 4 µm.

(Fig. 9)The density of diatoms was up to ﬁve cells per
SEM stub, which was quite low. Since many diatoms were found using a metallurgical microscope, a higher number of diatoms had been
expected.
Discussion
The tablets, from which the samples weretaken, were chosen based on the microscopic
observation prior to sampling. However, samples
were not necessarily removed from exactly the

104

Akihiro Tuji et al.

Figs. 4–9. 4. A clay cuneiform tablet BM28109 in BM (Courtesy of the Trustees of the British Museum). 5. Diatoms observed using SEM on tablet BM28109. Nitzschia palea (Kütz.) W.Sm. Length: 27 µm, breadth:
4.5 µm, striae 34/10 µm (Courtesy of the Trustees of the British Museum). 6, 7. Diatoms observed using LM
on tablet BM28109. 6: Nitzschia sp., 7: Small penate diatoms? (Courtesy of the Trustees of the British
Museum). 8, 9. Diatoms observed using SEM on tablet BM104703. 8: Stephanodiscus minutulus (Kütz.)Cleve et Möller. Diameter: 4 µm. 9: Discostella Houk et Klee sp. Diameter: 3.5 µm (Courtesy of the Trusteesof the British Museum).

Diatom Analysis of Cuneiform Tablets

same place (i.e., a cracked surface), where thediatoms were observed, as this might have significantly damaged the tablet. Instead, an extremely
sharpened tungsten needle was used to obtainsamples from sections which appeared better
able to withstand any damage that might becaused by sampling. We expected that tablet clay
would include many diatoms throughout, having
identiﬁed the presence of diatoms in one section.
However, if the presence of diatoms was limited
to a particular part of the tablet, it would havebeen necessary to pinpoint that exact section, andobtain samples from there.
Furthermore, diatoms found in this study arethose commonly found in freshwater bodies.
Nitzschia palea is an indicator species for polluted/eutrophic rivers (Watanabe et al., 1990;
2005). Stephanodiscus minutulus and Discostellaspecies are found in shallow freshwater ponds
and lakes (Krammer and Lange-Bertalot, 1991,
Tuji and Houki, 2001; Tuji and Williams, 2006a,
2006b). These diatoms are very common species,
and it might be that contamination took place
after the tablets were buried. However, it isunlikely because these tablets were buried duringsite abandonment and archaeosediments rarely
contain high numbers of diatoms. Another possibility is that contamination occurred during conservation. Freshwater (i.e., tap water) was usedin the desalinization treatment, though it is very
unlikely that the water used for conservation was
polluted as indicated by the species Nitzschia
palea. Both untreated fresh water and tap water
may of course contain freshwater diatoms. In
order to clarify the possibility of contamination,
it is necessary to investigate the history of theconservation treatments applied to these tablets.
We do not know, however, whether the unsuccessful detection of diatoms was due to the ﬁring
process of tablet conservation. As diatoms disappeared in ancient ﬁring clay pots made of disaggregated diatomaceous rocks according toMatsuoka and Suzuki (2014), the ﬁring process
might be effected the preservation of diatoms intablets.
Another possibility is that diatoms are present

105

in the samples, but the treatments that have been
applied have not been sufﬁcient to reveal them.
We considered the possibility that the diatoms
were covered with consolidated sediments suchas calcium compounds, which made them invisible under the SEM. We tried to rectify this byusing the acid treatment described above. Since
no diatoms were found after this treatment using
light microscopy, the presence of calcium compounds cannot be the reason why we cannot
detect diatoms. Another possibility is that thediatoms are being covered with clay particles.
However, such clay particles, even if present,
would have been washed out through the 1.2 µm
ﬁlter paper. We have so far applied all available
methods to identify diatoms in the very small
samples provided. The fact that no signiﬁcantpresence of diatoms was detected could indicate
either that there were no diatoms in the original
tablet clay or that the concentration of diatoms inthe sediment was far lower than expected. In thelatter case, there is a method of increasing theconcentration of diatoms by using heavy liquids(Meyer et al., 2012). However, this method
requires larger amount of examined samples,
which is not possible from these high value cultural materials.
It is, however, puzzling why so few diatoms
were discovered in the clay samples we examined, especially since the presence of diatoms
was conﬁrmed under the microscope on thecracked surfaces of tablets. The lack of diatoms
in these tablet clay samples, unfortunately, makes
the original purpose of our research (tracing
environmental changes) difﬁcult to achieve―we
had intended to examine the level of salinity ofriver water and link it to the precise dates asrecorded in the texts on the tablets.
The fact that these samples seem to containfew or no original diatoms, however, may shed
new light on some as-yet-unknown aspects of thetype of source material chosen for manufacturing
clay tablets. Our separate investigation of modern river sediment in the vicinity of ancient
Umma revealed recently that ﬁne sediments
exposed on a riverbank do not seem to be associ-Akihiro Tuji et al.

106

ated with diatoms. We examined four different
sediment samples taken from different samplingsites along a tributary of the Tigris (Tuji et al.,personal information): two were dry sediments
and two were wet. The dry sediment samples
contained many ﬁne grains, but no diatoms. The
wet sediment samples, however, contained diatoms, and these samples seem to have been collected from a site in which the sediment was stillin contact with river water. In other studies in the
Near East, it was found that phytoliths and othermicrofossils migrated down sandier strata to themore ﬁne ones, such as clays (Marsh, 2014), andthis may be the case with the diatoms here. This
provisional study may indicate what type ofsource material was originally collected. It may
be that alluvial sediments dominated with ﬁnesands and silts were deliberately chosen for these
economic tablets, which were more disposable
and ﬁner clays were used for the more literarytexts. In order to establish this, however, we needfurther study and evidence.
Acknowledgments
The authors would like to express sincere gratitude to the Trustees of the British Museum, Dr
David Saunders (Keeper, Department of Conservation and Scientiﬁc Research, the British
Museum), Dr John Curtis and Dr Jonathan Tubb
(Keepers, Department of the Middle East, theBritish Museum), and Dr Catherine Higgitt(Head of Science Group, Department of Conservation and Scientiﬁc Research, the British
Museum) for granting permission to conduct
these analyses. We would also like to thank Dr
Yoshihiro Tanimura, National Museum of Natureand Science, and Dr Noritoshi Suzuki, Tohoku
Univeristy, for their helpful advice on diatom
acidiﬁcation procedures. This research was supported ﬁnancially by the Research Institute for
Humanity and Nature, Kyoto, and by JSPS
KAKENHI Grant Numbers 23310190 and
24401016 (C. Watanabe).

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