Sa Huynh and Cham potteries: microstructure and likely processing
Philippe Colomban a,*, Doan Ngoc Khoi b, Nguyen Quang Liem c,Cecile Roche a, Gerard Sagon a
a Laboratoire de Dynamique, Interaction et Ractivit (LADIR), UMR 7075, Centre National de la Recherche Scientifique,Universit Pierre et Marie Curie, 2, rue Henri Dunant, 94320 Thiais, France
b Museum of Quang Ngai Province, Quang Ngai Town, Viet Namc Institute of Materials Science, National Centre for Natural Science and Technology of Viet Nam, 18 Hong Quc Vit, Cu Giy, Hanoi, Viet Nam
Received 6 November 2002; accepted 16 June 2003
Various techniques such as Raman spectroscopy, X-ray diffraction, and thermal expansion measurement have been applied to Sa Huynh(10th century BC2nd century AD) and Cham (215th centuries AD) pottery findings from the excavations at Quang Ngai province (CentralViet Nam). The experimental results highlight the microstructure and technological processing of these potteries. Sa Huynh potteriestechnology is based on iron-rich clay-based body and feldspar fluxing agents. The firing is made in more or less strong reducing conditions.The Cham potteries were made from high-temperature fired silica-rich bodies covered with thin colourless to blackbrown glazes. 2004 Elsevier SAS. All rights reserved.
Keywords: Sa Huynh; Cham; Pottery; Microstructure; Ceramic processing
1. Research aims
Pottery relics found in various sorts and were produced inViet Nam since long time, much earlier than the 10th centuryBC . During the period of time between the 87thcentury BC and several centuries AD, two different culturesexisted, the Dng Son in North Viet Nam and Sa Huynh inCentral Viet Nam  existed. The Sa Huynh culture wascontinued/replaced by the Cham culture in the 2nd centuryAD. The cultural relics of the latter two were found frommany excavations . Among the relics found, the pot-teries are large in amount and very important from the his-toric and technological points of view. It is to be noted thatpotteries were produced for many different purposes liketools for living peoples, ritual wares for certain religions etc.On the other hand, depending on the technological capability,the potteries could be prepared and classified in various sorts:terra-cotta, earthenware, stoneware, etc. [13,14]. From thefunctional and outward appearances one can see potteries asindicators for a certain history and civilisation. From the
technical features they show the science and technologyimprinted. These two features appear in the inter-dependentcorrelation, i.e. the more advanced is the civilisation and viceversa. In addition, the potteries were made from startingmaterials (refractory sand and clays, fluxing agents likewood-ash, chalk or shellfish) with well-defined firing proce-dures. These make the potteries specific to the kiln and themaker. Using the materials science techniques one can searchback the composition and processing which were applied atthe production time .
In this paper, we present the first results obtained from theSa Huynh potteries made during the 10th century BC to ADand the Cham potteries produced during the 915th centuriesAD. The various techniques used followed closely the pot-tery technology, which enables us to discuss about the pot-tery processing at ancient time. The quantitative data of themicrostructures and structural phases not only show the his-toric features but also play an important role as a gooddatabase for the future work on similar potteries.
2. Samples and experiments
Samples were selected from the excavations at Ly Sonisland, which belongs to Quang Ngai province in the North of
* Corresponding author.E-mail address: email@example.com (Ph. Colomban).
Journal of Cultural Heritage 5 (2004) 149155
2004 Elsevier SAS. All rights reserved.doi:10.1016/j.culher.2003.06.005
South Viet Nam (see, maps in Fig. 1). The Ly Son strata (orcultural layers) were very stable, which helped to date thesamples. The production times and optical images of samplesare presented in the first two columns of Tables 1 and 2. Allthe Sa Huynh potteries (six samples M19M9, named by theQuang Ngai Museum) are un-glazed terra-cotta with rathercoarse grains (in some samples grain sizes as high as 1 mmwere observed), outer reddish-brown colour and more or lessblack core in cross-section view. Samples M14 and M9 (seethe images in Table 1) were decorated at the exteriors bygrooving in parallel lines. The Cham pottery M3 is made ofwhite body coated with a very thin colourless glaze, while theM2 (the 15th century sample) is glazed in blackbrowncolour, a typical style of the Cham pottery .
For the direct observation of sample fracture, a high reso-lution (1200 1600 dpi) scanner was used. The sinteringtemperatures that the samples had experienced at the produc-tion time were estimated by measuring the thermalexpansion/shrinkage evolution between room temperatureand 800/1400 C.A DI 24 dilatometer (Adamel, France) withalumina rod and sample support was used for temperaturesup to 1400 C.
To study the structural phases, we used two differenttechniques. One is X-ray diffraction on powdered samplesusing a PW 1830 X-ray diffractometer (Philips, The Nether-lands). Comparison with the JCPDS Database and calcula-tion of the unit-cell parameters were made using DIFFRAC-plus software (Bruker, Wissembourg, France). A crystallinephase of ~1 wt.% could be detected. The other technique isRaman scattering. Non-destructive measurements weremade using spectrometers from Jobin Yvon (XY system or
Infinity, France) with a Spex CCD 2D matrix (2000 256)for signal detection. No sample preparation was needed. TheRaman cross-section depends on the chemical bond: themore covalent is the bond, the more electrons are involved inthe bond and the higher is Raman intensity, whatever thecrystallinity. Thus, X-ray diffraction and Raman scatteringdo not obey the same phenomenon and complete each otherfor structural phase detection. In the case of pottery, a com-posite or micrometer-sized multi-phase material, Ramanspectroscopy has proved to be a unique technique for study-ing the microstructure (with micrometer spatial resolution)and related production technology [15,1922]. Details of theexperimental set-ups were described elsewhere [15,1923].
The usual Archimedean method for measuring the openporosity was not applicable for samples containing more orless incompletely fired carbonate (giving rise to CaO that wasthen hydrolysed with water), rather micro-cracked and easilycrumbled in water. We used an alternative and suitable tech-nique to avoid the use of water. The usual constituent phases,like quartz and others minerals, have approximately the samemass density, ~2.5 g cm3. Then, from the measurable sizesof the samples under study, we have estimated the corre-sponding porosities by comparing the calculated weight(equal to the product of mass density and volume) and realweight of sample. Practically, this technique is very appli-cable for the high porosity matters for which the accuracy(510%) could be well acceptable. The breakability andpowderability in an agate mortar was used to estimate themechanical strength of each sample. Results were expressedusing a qualitative scale.
< 8th BC 8th BC 2th AD
Fig. 1. Map of Viet Nam and insert the expansion showing the Ly Son island, Quang Ngai province. The Sa Huynh/Cham culture was settled down during the8th BC15th AD centuries in the field land from Hue to the North of Ho Chi Minh city.
150 Ph. Colomban et al. / Journal of Cultural Heritage 5 (2004) 149155
Table 1Production times, micrographs and main structural phases of the BC Sa Huynh potteries. The upper part of each image was taken in cross-section and the lowerone on the surface of the corresponding sample. The sizes of the lower images are 4 cm 2 cm, while the corresponding uppers are magnified six times.Microstructure and main phases of Sa Huynh potteries (BC)
Micrographs ( 1 x 0.5 cm) ( 4 x 2 cm)
RAMAN X-ray diffraction
M 19 1000 BC
Carbon, Quartz Orthoclase
Fe2O3, epidote Albite ?, glass ?
M 17 1000 BC (+++)
Quartz, Orthoclase Fe2O3,
glass ?, Spinel ? Carbon
Quartz +++ Albite +
Enstatite +(cristobalite ?)
M 16 1000 BC
Enstatite ?, Quartz CaCO3 (aragonite)
Britholite ? Carbon
Quartz +++ Albite ++Hmatite
M 14 1000-500
Hematite, magnetite Spinel, Orthoclase
Quartz, Amphibole ?
M 12 500-0 BC
Enstatite ?, Fe2O3Feldspar (Albite or
Quartz +++ Albite +
Cristobalite +Enstatite +Hematite
M 9 500-0 BC
Quartz, Albite Hematite
Microstructure and main phases of Sa Huynh potteries (BC)
Peak intensity and mechanics: + weak; ++ medium; +++ strong. Salient features in bold; n.s.: not studied. Photo sizes are given for the upper and bottom(section) views.
151Ph. Colomban et al. / Journal of Cultural Heritage 5 (2004) 149155
3. Results and discussion
3.1. Optical images, sintering process and open porosity
The cross-section and surface images of Sa Huynh andCham potteries are illustrated in column 2 of Tables 1 and 2,respectively. Most optical images taken in cross-sectionshow porous bodies with white spots. The voids are clearlyseen differently from sample to sample. The outer parts of thebody are usually reddish-brown and the inners are black.These colours are well understood features of the potteriesmade of clays containing iron and organic compounds. Ironoxidation gives rise to a-Fe2O3 formation on the outer layers.The red colour is usually assigned to trivalent iron ions in thesolid solution of spinel Fe2O3 and alumina [24,25]. Thereducing firing atmosphere gives rise to a black core becauseof the formation of C and FeO.
One of the most important information concerning thetechnology applied to produce ceramics is the firing tempera-ture and the duration of the thermal cycle. The knowledge ofthe firing temperature gives information about the kiln per-formance that is suitable for certain kinds of potteries. For agiven firing temperature, e.g. 1200 C the choice of the rawmaterials combination makes it possible to prepare variouskinds of earthenware, faience, stoneware or porcelain, eachone exhibiting different properties (colours, thickness, po-rosity, strength, etc.). In other words, all properties character-istic of a certain ceramic are in causality relationship with thestarting compositions and firing procedure. Obviously, thepalette of possibility decreases with the firing temperature.Basically a pottery is obtained by firing a mixture of quartzsand, clays and fluxing agents like wood-ash, feldspar, shell-fish or chalk. The mixture is homogeneously prepared usingwater and is then hand-shaped, with or without some ancil-
lary equipment (wheel, mould...) to obtain the expectedshape. The use of characteristic clay(s) plays a key role inachieving the ceramic properties. The tempering grains, likequartz sand, etc...., limit the shrinkage of the paste and,hence, hinder the cracking of the item after drying. Duringthe firing, the following phenomena take place: (i) below200 C the elimination of the water adsorbed on and betweenthe clay particles; (ii) between 300 and 700 C dehydroxyla-tion of the clays promotes the formation of very reactiveamorphous materials which could react with inert grains; (iii)between 700 and 1200 C, decomposition of carbonates withformation of liquid phases at the contact between grains offeldspar/lime/phosphate/FeO etc.... (e.g. see the Na2OFeOSiO2 (#497) and SiO2NaAlSiO4FeO (#853) phase dia-grams in Ref. ) and of products from the thermally-decomposed clays; (iv) above 12001300 C, crystallisationto form mullite and cristobalite takes place. Special phaseslike wollastonite polymorphs, calcium phosphates can alsobe formed in Ca-rich compositions. All the above reactionsneed temperature and time to complete and contribute to theformation of a dense pottery body. Observed sets of phasesinform on the firing temperature. For instance carbon, (re-duced) iron oxides (e.g. magnetite (Fe3O4) or even wustite(FeO)) demonstrate reducing firing. Note that wustite acts asa fluxing agent to promote the low-temperature sintering ofaluminosilicates. The shrinkage measurement of ancient ce-ramics is also a good method to determine their sinteringtemperature. For temperatures lower than the firing tempera-ture (close to 0.9 Tf), we must observe the mean thermalexpansion of the set of the phases constituting the body.When the temperature approaches the initial firing tempera-ture, reactions, which were not finished during the first heat-ing cycle start again and new reactions, those requiringhigher temperatures, also begin [1316,2729]. Phase deter-
Table 2Production times, micrographs and structural phases of t he AD Cham ceramics (see Table 1 caption). Microstructure and main phases of Cham ceramics (AD)
Micrographs ( 2 x 1 cm)
( 1 x 0.5 cm)
RAMAN X-ray diffraction
M 3 800-900 AD (glazed)
Rutile, Cristobalite Quartz, Gypse
Quartz +++ Cristobalite ++
M 2 1400-1500
Rutile, QuartzCO3 (calcite ?)
Microstructure and main phases of Cham ceramics (AD)
Peak intensity: + weak; ++ medium; +++ strong. Salient features in bold; n.s.: not studied. Photo sizes are given for the upper and bottom (section) views.
152 Ph. Colomban et al. / Journal of Cultural Heritage 5 (2004) 149155
mination and sintering temperatures can then be used torecognise the original technological route.
3.2. Raman spectroscopy and X-ray diffraction
Fig. 2 shows the Raman spectra of typical structuralphases from the Sa Huynh and Cham potteries. Phases de-tected by X-ray diffraction are listed in Table 1 and comparedwith the results of Raman microspectrometry analysis. Ob-served phases are: a-quartz, albite, orthoclase, rutile, mullite,aluminosilicate glass, etc. a-quartz, albite and orthoclaseremain from the starting materials, while mullite, cristobaliteand aluminosilicate glass result from the high-temperaturefiring. The existence of orthoclase and albite is a proof for theuse of feldspar as an ingredient. Examination of the micro-structure by Raman micro-spectroscopy shows the complexassociations of quartz and feldspar in many grains. Suchassociation is typical for rocks like granite, rhyolithe andtheir degradations. Geography and geology of Central VietNam  show that such kinds of rocks exist near theexcavation site. Clays are very common in many places. Thisindicates that the raw materials were locally exploited andused by ancient potters. Note that a very small volume (in theorder of several square micrometers) can be examined usingthe micro-configuration of Raman spectroscopy. Thus,phases in small amounts, which can not be detected onclassic X-ray powder pattern, could be clearly observed byRaman microspectrometry. In some case the identification byRaman spectroscopy is rougher than that by X-ray diffraction(e.g. Raman can not easily recognise albite from orthoclase).The structural phases observed by X-ray diffraction andRaman spectroscopy showed a good agreement (see RamanDatabase in Refs. [20,31,32]). Moreover, the structuralphases existing in potteries show the very nice consequencesof the applied technology. Ca was used as the fluxing agent inall samples and helped to promote the sintering process. Insample M7, a large amount of aluminosilicate glass wasdetected. In only M16 sample was aragonite clearly observedby Raman spectroscopy (see, the corresponding spectrum in
Fig. 2). The presence of aragonite may be an indication forthe use of shellfish as a CaO source. However, X-ray diffrac-tion did not show the same evidence and the general use ofshellfish is not ascertained. Also, because of the high firingtemperature the primary aragonite could be transformed intoother phases.
Raman check of the reddish-brown (outer layers) andblack (inner core) parts of potteries shows the existence ofhematite and carbon, respectively, as already mentionedabove. The 1320 cm1 Raman scattering band is the finger-print for a-Fe2O3 that resulted from the light scattering onmagnons, while the two broad bands at 1350 and 1600 cm1
come from carbon. One should note that in many bricks theouter appears to be red while the inner as a black or metallic-black colour. The red colour originates from the trivalent ironion in the solid solution of spinel Fe2O3 and alumina but theblack colour originates from the reduced iron oxides such asFeO or Fe3O4. Careful examination of the sample grainsshows that hematite is generally found as inclusions in quartzgrains, indicating that hematite or magnetite appeared as thesecond phases in quartz rock.
Most of the terra-cotta samples exhibit a Raman spectravery similar to that of dioptase, a copper silicate. In fact,X-ray diffraction failed to detect a significant amount ofdioptase but it clearly detected enstatite. Because the Ramanspectra of these two phases are rather similar, the assignmentof the observed phase to enstatite FeMg solid solution ismore reasonable. Enstatite is rare from raw materials andcould, therefore, be considered as a fingerprint for the mate-rial used. In M2 and M3 samples, trace of rutile, a TiO2polymorph were observed. However, it may be an impurityfrom quartz sand use. These two potteries were reasonablyproduced with silica-based technology. The observation ofmullite in sample M3 is in good accordance, showing itsreally an aluminosilica-based composition fired at high-temperature.
Our experimental data including optical images, structuralphases, and porosity of the Sa Huynh potteries are presentedin Tables 1 and 2. To make things easier for the readers, the
400 800 1200 1600
206 700 1085
b) calcite + carbon
.u . a / yt isn etnI nam a
Wavenumber / cm-1400 800 1200 1600
d) magnetite + wustite
a) glassy phase
.u .a / yti sn etnI nama
Wavenumber / cm-1400 800 1200 1600
604 921 1091
661 962 1007
i) cristobaliteh) mulliteg) albite
b) dioptase ?
.u .a / ytisn etnI nama R
Wavenumber / cm-1
Fig. 2. Typical phases observed in the Sa Huynh/Cham potteries by Raman spectroscopy. They are classified into (A) carbonate, (B) silicate and (C) oxidegroups. The phase names are indicated on each curve.
153Ph. Colomban et al. / Journal of Cultural Heritage 5 (2004) 149155
names and chemical formulae of the structural phases ob-served are presented in Table 3. Each comment in the tablesis explained in their caption.
3.3. Thermal expansion/shrinkage
Fig. 3 shows the features of expansion/shrinkage fromseveral representative Sa Huynh and Cham potteries thatillustrate the discussion above. The characteristic ab phasetransition of quartz at 573 C is clearly seen (in samples M3,M12 and M16) and the evolution with temperature is verydifferent from sample to sample. For sample M17, theshrinkage curve appears as a stepped down at around 850 Cwhich demonstrates that the item was well-sintered, i.e. that aliquid phase occurred to promote a good sintering. The 5%low porosity and rather elevated hardness are also natural
consequences of a good pottery technology. The significantamount of aluminosilicate glassy phase detected by Ramanspectroscopy in M17 sample is with it. The fluxing agenthelped reactions between solid grains because it becameliquid at a temperature much lower than the other constitu-ents. As already discussed above, the sintering of potterydepends on the combination of the starting raw materials.Besides, the grain sizes of ingredient solids significantlycontribute to the sintering completion. If the grain sizes of thestarting raw materials are sufficiently small and the volumeof liquid phase sufficient to wet the grain boundaries conve-niently during firing, then sintering is more complete and thepottery is denser after heat processing. If the reaction be-tween solid coarse grains took place at their contacts or grainboundaries only, then the outer part of these grains melted tostick them together. This seems to be the case for the highporosity potteries, e.g. sample M2. We found that it was firedat >1200 C but that the sintering did not take place, since theporosity remains very high (>40%) and hardness is low. Theobservation of mullite and cristobalite in this sample is ingood agreement with the high-temperature firing. Fig. 4illustrates the firing temperature, porosity, and mechanical
Table 3The names and chemical formulae of structural phases observed in SaHuynh/Cham potteries
Name Formula FamilyAlbite NaAlSi3O8 FeldsparAmphibole (Na, K)(Ca, Fe)2Al5Si8O22(OH)2 SilicateAragonite CaCO3 OxideBritholite (Ca, Y)5((SiO4, PO4)3(OH, F) SilicateCalcite CaCO3 CarbonateCristobalite SiO2 SilicateDioptase CuSiO2(OH)2 SilicateEnstatite (Mg, Fe)Si2O6 SilicateEpidote Ca2(Al, Fe)3(SiO4)3OH SilicateHmatite Fe2O3 OxideMagnetite Fe3O4 OxideMuscovite KAl3Si2O10(OH)2 SilicateOrthoclase KalSi3O8 SilicateQuartz SiO2 OxideRutile TiO2 OxideSpinel XAl2O4 OxideWollastonite Ca3(Si3O9) SilicateWustite FeO Oxide
0 200 400 600 800 1000 1200
Temperature / CFig. 3. The heating/cooling cycles of representative Sa Huynh/Cham potte-ries. M17 sample is well-sintered at low-temperature while the others,although fired at much higher temperatures (see, e.g. M3) are poorly sinte-red. The bump at 573 C corresponds to the ab phase transition of quartz.
M 17 M 16 M 14 M 12 M 3 M 2
C / erutarepmeT gniriF
M 19 M 17 M 16 M 14 M 12 M 9 M 3 M 2
% / ytisoroP
M 19 M 17 M 16 M 14 M 12 M 9 M 3 M 2
/ htgnertS lacinahceM
Fig. 4. From top to bottom: firing temperatures (the two bars give theminimal and maximal estimation) deduced from the shrinkage curvesmeasured on Sa Huynh/Cham potteries; open porosities; and mechanicalstrength in arbitrary units.
154 Ph. Colomban et al. / Journal of Cultural Heritage 5 (2004) 149155
strength of the Sa Huynh and Cham potteries. We see that therecent items were fired at rather high-temperatures. Making acomparison of pottery properties between the samples understudy gives the result that the oldest sample, M17, was firedat rather low-temperature (850900 C) but had the bestcharacteristics: high densification and high mechanicalstrength (Tables 1 and 2).
Ancient Vietnamese potteries found at Quang Ngai prov-ince and made during the period of the Sa Huynh and Chamcultures were studied by various materials science tech-niques such as optical imaging, Raman spectroscopy, X-raydiffraction or thermal expansion measurement. Based on theexperimental data, we present the microstructures of theseancient potteries in relation with their technological process-ing. The Sa Huynh potteries are classified as terra-cotta, themost prominent features being a clay-based body and feld-spar fluxing agents. The Cham potteries were made of high-temperature fired silica-rich bodies and thin colourless orblackbrown glazes.
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Sa Huynh and Cham potteries: microstructure and likely processingResearch aimsSamples and experimentsResults and discussion3.1. Optical images, sintering process and open porosityRaman spectroscopy and X-ray diffractionThermal expansion/shrinkage