Branko Crnković

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B. CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.S., XXIII125-138 (1990) 125BRANKO CRNKOVIĆ - DRAGUTIN SLOVENEC - ANA SOKACFaculty of Mining, Geology and Petroleum Engineering, University of Zagreb41000 Zagreb, Pierottijeva 6CERAMICS FROM THE ROMAN CITY OF SALONA NEAR SPLITUDC 904:738.8 (36:497.13)Original scientific paperCeramics from the Roman city of Salona were examined by optical microscopy,X-ray diffraction, and by micropaleontological and chemical methods. It wasconcluded that a portion of the ceramics voas made of the raw material fromthe sediments of Eocene flysch in the immediate surroundings of Salona, andthat the firing temperatures ivere betvueen 800" and 850"C.IntroductionThe Roman city of Salona near Split (Fig. 1) had the status of a Roman colonyand was especially prosperous in the time of the emperors Trajan, Hadrian, AntoninusPius and Diocletian. The urban nucleus of Salona with ports, walls, forum, theatres,temples, baths and private villas was formed in the 2nd century A. D. The large amphi-theatre from the 2nd century was incoporated into the town fortification system.Du.llovo7 knFigure laArchaeological studies in the area of Salona, along the newly built Splitbypass,were carried out in 1986 and 1987. On that occasion Roman architecture was discoveredat the locations of the »Ancient street« and the Hortus Metrodori necropolis, Many ofmovable archaeological objects were also found. Teams from the Croatian RestorationInstitute from Zagreb and the Archaeological Museum from Split collected samples of126 B. CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.s, XXIII125-138 (1990)stones, mortar and ceramics, before the site was covered again to allow the constructionof the bypass. Part of the samples collected was analyzed by optical microscopy, paleon-tological, X-ray diffraction and chemical methods.The present paper describes preliminary results of the examination of ceramicsamples. Special attention was paid to the origin of the raw material used in ceramicspreparation and the firing temperature of the ceramics.The samples analyzed were marked RZH-2146 and RZH-2147. They were takenat the site of the »Ancient street«. The sample RZH-2146 was taken from a dike on thenorthern side of the street, while the sample RZH-2147 was found in the southern forkof the street under a well preserved antique mosaic (from Malinar and Smailagić, 1987).Methods of analysisThe ceramic samples were examined by optical microscopy, X-ray diffractionand by chemical methods.A polarizing microscope was used to determine the composition of the ceramicsand the microorganisms contained in the samples.X-ray powder diffraction was used in order to determine the mineral compositionof the ceramics, and the composition of the supposed raw material from the immediatesurrounding of Salona, clay sediment of the Eocene flysch from the locality of Duilovo(Fig. 1). The flysch from Duilovo was used to prepare a composite material in a simu-lation procedure of the ceramics firing. The composite material and the antique cera-mics RZH-2146 were fired at a series of temperatures. The phase composition of thefired samples was found for each temperature, and on that basis the firing temperatureof the Salona ceramics was determined. X-ray powder diffraction patterns were takenby means of the counter diffractometer, with CuK a radiation. The minerals were deno-ted in diffraction patterns as follows (Figs. 4-6):I - illiteQ - quartzP - plagioclaseK - potassium feldsparCa - calciteC - calcium oxideH - hematiteGe - gehleniteD - diopsideThe chemical composition of one ceramics and of the insoluble residue of theflysch were determined by the classical quantitative chemical silicate analysis.Results of examinationsTwo ceramic samples were examined.The first sample from ceramics RZH-2146 was 6 to 7 mm in thickness and washalf red and half yellow in colour, with smooth surfaces on both sides.The second sample from ceramics RZH-2147 was 5 to 7 mm in thickness, andwas red throughout, with a furrowed convex part so that it resembled a furrowed shell.B. CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.s., XXIII125-138 (1990) 127Figure lb128 B.CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.s., XXIII125-138 (1990)Figure 2B. CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.S., XXIII125-138 (1990) 129Figure 3130 B. CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.s., XXIII125-138 (1990)M i c r o s c o p i c a n a l y s e sThin sections of the ceramic sample RZH-2146 from two differently colouredparts, did not show a difference in the mineral composition, but only in the appearanceof the microscopically indeterminable matrix. Anisotropic effects were slightly visiblein the matrix of the red part, whereas the matrix of the yellow part was vague andpartially non-transparent.The ceramics contained the following microscopically determined components:an abundance of well preserved calcite skeletons of foraminiferes (Fig. 2), particles ofquartz and an amount of quartzite, chalcedonic chert, feldspars, microscopically minu-te calcite irregular aggregates, muscovite-sericite, epidote, an opaque mineral and tour-maline.The dimensions of the components were as follows: foraminifers having the dia-meter up to 0.25 mm, quartz particles of the diameter up to 0.22 mm, grains having insections up to 0.24 x 0.32 mm2, quartzite particles with the diameter up to 0.28 mm,muscovite lamina uptoO.02xO.15 mm2, and the aggregates of fine-grained calcite upto 0.25 x 0.30 mm2.The skeletons of the foraminifers, made of calcite, were thin with central partsporous and empty. Quartz grains were angular in shape, or they were cracked. Quartzitehad a granoblastic texture, while tourmaline was clearly pleochroitic.A thin section of ceramics RZH-2147 contained the same components as the sam-ple RZH-2146 described above (Fig. 3). The skeletons of foraminifers in this samplewere not well preserved and were partly distorted. Quartz grains of diameters from0.15 to 0.38 mm, were angular in shape, or partly cracked. The ceramics also containedsmall fractions of feldspars (microcline), quartzite, chalcedonic chert and tourmaline,as well as aggregates of microcrystalline calcite.The calcite skeletons in the ceramics RZH-2146 were represented by the follo-wing foraminifers:Globigerina yeguensis (WEINZIERL & APPLIN)Globigerina sp. div.Globorotalia sp.Globigerinatheca ex gr. mexicana (CUSHMAN)G. mexicana kugleri (BOLLI, LOEBLICH & TAPPAN)Turborotalia cerroazulensis frontosa (SUBBOTINA)T. cerroazulensis premoli (TOUMARKINE & BOLLI)? Bulimina sp.NodosaridaeThe stratigraphic affiliation of the foraminifers can be stated as Middle Eocene(Lutetium).The calcite skeletons in the ceramics RZH-2147 were represented by the follo-wing foraminifer genuses:GloborotaliaGlobigerinaPseudohastigerina? GlobigerinathecaB. CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.s., XXIII125-138 (1990) 131X - r a y d i f f r a c t i o n a n d c h e m i c a l a n a 1 y s i sThe ceramics RZH-2146 was analysed chemically (Table 1) and by X-ray powderdiffraction. The diffraction patterns were taken of the as-found (original) sample, andthe ceramic sample treated by 1.5% acetic acid for 10 minutes (Fig. 4). It was foundthat the ceramics contained calcite (22%), quartz (15%), plagioclase (5%), and smallamounts of illite (or muscovite), hematite, potassium feldspar, gehlenite, diopside andan amorphous fraction. The ceramics probably contained also a fraction of structurallyunidentified calcium-aluminium-silicate hydrates; this conclusion was based on theweight loss (of 6.17%) during heating up to 600°C (Table 1). Bulk pieces of the ceramics(not the powder) were baked at 750°C, 800°C and 900°C for 3 hours. According to thepowder diffraction patterns of these samples (Fig. 5), diffraction line intensities of ge-hlenite and diopside (characteristic silicate minerals in ceramics) increased with theincrease of temperature. Diffraction patterns of the fired samples did not contain dif-fraction lines of calcite. Calcite was decomposed at a temperature below 750°C; thecalcite of foraminifers transformed mainly into calcium oxide, while the dispersed cal-cite, with fine grains, reacted with silicates forming calcium silicates.A sample of the Eocene flysch from the locality of Duilovo was selected, contai-ning ~ 45% of calcite. The calcite in this sample was solved in 1.5% acetic acid, andthe insoluble residue was analysed chemically (Table 1) and by X-ray powder diffrac-tion. The approximate mineral composition of the insoluble residue was as follows(weight percent): 25% of illite, 23% of quartz, much of irregularly interstratified phyl-losilicates and an amorphous fraction, 20% of smectite and vermiculite, 6% of plagioc-lase, and small amount of chlorite and potassium feldspar. One can see from Table 2that the ratios of chemical components (oxides) in the ceramics and flysch were rathersimilar. Therefore, the insoluble residue of flysch could be used to obtain the compositematerial in a simulation procedure of the ceramics preparation. The amount of calcitein the raw material used in preparation of the antique ceramics, according to the datafor calcium in Table 1, was ~ 30%. Therefore, the composite material was prepared tohave the following composition (weight percent): 70% of the insoluble residue, 20% ofpowdered calcite and 10% of the calcitic Eocene foraminifers (grains having 0.3 to 0.2mm in diameter). The composite material was fired for 3 hours at 750, 800, 850 and900°C and X-ray powder diffraction patterns of these samples were taken. The samplefired at 750°C did not any more contain calcite. X-ray diffraction pattern of the samplefired at 800°C contained weak diffraction lines of gehlenite and diopside. Diffractionlines of gehlenite and diopside became stronger and well-defined as the firing tempera-ture incrased. Diffraction pattern of the sample fired at 850°C still contained diffractionline of illite at 0 ~ 10°, but the structure of illite was destroyed after firing at 900°C.Diffraction patterns of the composite material and of the ceramics RZH-2146fired at the same temperatures were almost identical. These two samples possessed avery similar mineral composition after the same thermal treatment. For instance, bothsamples when fired at 900°C (Fig. 6) had the following mineral composition: quartz,gehlenite, diopside, calcium oxide, plagioclase, hematite, potassium feldspar and anamorphous fraction.X-ray powder diffraction was also used to analyse the ceramics RZH-2147. The132 B. CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.s, XXIII125-138 (1990)mineral composition of this ceramics was different from that of the ceramics RZH-2146.The following minerals were identified in RZH-2147: 36% of quartz, 20% of calcite,small fractions of plagioclase, potassium feldspar and hematite. The firing temperatureof this ceramics has not yet been determined.D i s c u s s i o n a n d c o n c l u s i o nOn the basis of the microscopic, X-ray diffraction and chemical examinations itwas established that a portion of the antique ceramics found in the »Ancient street« inSalona was made of a clayey raw material found in the flysch sediments of MiddleEocene age in the immediate surrounding of Salona.The stratigraphic affiliation of the clayey material used in the production of theceramics was confirmed by the microscopic determination of the relatively well preser-ved foraminifers of the ceramics. Calcite skeletons of the foraminifers underwent thepreparation and processing of the clayey raw material, as well as firing ceramic pro-ducts. During the firing process calcite of the microorganic skeletons turned into CaO.Calcium oxide exposed to moisture transformed into Ca(OH)2, and the latter, being incontact with carbon dioxide, transformed back to the stable calcium carbonate, calcite.The forms of the foraminifer skeletons remained almost unchanged, having undergoneonly slight distortions, as observed by means of optical microscopy.Therefore, it was concluded according to the present mineralogical study of theantique ceramics and the Eocene flysch from Duilovo, that the raw clay material forpreparation of the ceramics was taken in an immediate surrounding of Salona. Theratios of the oxide fractions in the ceramics and flysch were very similar. The mineralcomposition of the fired composite material was very similar to that of the antiqueceramics RZH-2146. The ceramics originally contained illite (not destroyed during pre-paration) and relatively poorly defined gehlenite and diopside. Therefore, one couldconclude from the comparison of the diffraction patterns of the fired ceramics and ofthe composite material, that the firing temperature of the antique ceramics RZH-2146was probably between 800 and 850°C.Besides the ceramics described above,' one more ceramic sample was analysed byX-ray powder diffraction. This contained an amount of quartz similar to that in sam-ples RZH-2146 and RZH-2147, but it contained bigger amounts of plagioclase, potas-sium feldspar, hematite, muscovite and an unidentified mineral. The ceramics did notcontain calcite. It was obvious that the raw clay material, used in preparation of thatceramics, was different from that used in the ceramics RZH-2146 and RZH-2147, thatis, it did not originate from the Eocene flysch, found in the surrounding of Salona.Further examinations are needed to establish the origin and other properties of thatceramics.AcknovdedgmentsWe are grateful to the Croatian Restoration Institute, Zagreb, for the permissionto publish the present work. We would also like to thank the teams of the CroatianRestoration Institute and the Archaeological Museum, Split, who carried out the fieldwork on the site by collecting the samples. Our thanks are also due to Dr D. Šiftar whocarried out the chemical analysis of the ceramics and flysch.B. CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.s., XXIII125-138 (1990) 133ReferenceMalinar, H. and Smailagić, Lj. (1987): Elaborate - Conservatory protection ofarchaeological objects of ancient Salona in sectors »Ancient street« and »Hortus Metro-dori« (in Croatian: Elaborat - Zaštita arheoloških iskopina antičke Salone na sektorima»Antička ulica« i »Hortus Metrodori«), Croatian Restoration Institute, Zagreb.Table 1. The chemical composition of the ceramics and the flysch insoluble residue(weight percent)SiO2A12O3 + TiO2FeOFe2O3MgOCaONa2OK2OH2O (105°C)Ign.loss(105°-600°C)Ign.loss(600°-900°C)ceramicsRZH-214644.3512.53n.d.4.961.9218.070.901.521.874.309.46flysch,insol. residue56.9816.200.876.572.581.700.702.644.854.941.31Table 2.oxidesThe proportions of the oxides in the99.88ceramics andceramicsRZH-2146the99.34flyschflysch,insol. residueA12O3Fe 2 O 3MgOK2OMgO:SiO 2:S iO 2: S i O 2:S iO 2: A12O30.283 0.2840.112 0.1330.043 0.0450.034 0.0460.153 0.159FIGURE CAPTIONSFig. 1.Position map of Salona near Split, with the newly discovered Roman sites »Ancientstreet« (A) and »Hortus Metrodori« necropolis (B) and position of Duilovo eastof Split.134 B. CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.s., XXIII125-138 (1990)Fig. 2.Microphotographs of ceramic sample RZH-2146, shovving well preserved calcite skele-tons of foraminifers and particles of quartz and quartzite in the cryptocrystallinemicroscopically indeterminable matrix. Cross Nicols.Fig. 3.Microphotographs of ceramic sample RZH-2147, showing not well preserved and partlydistorted calcite skeletons of foraminifers and particles of quartz and quartzitein the microscopically indeterminable matrix. Cross Nicols.Fig. 4.X-ray powder diffraction patterns of ceramic sample RZH-2146 (a), and of the samesample after treatment by 1.5% acetic acid (b).Fig. 5.X-ray powder diffraction patterns of ceramic sample RZH-2146 fired for 3 hours at750°C (a), 800°C (b) asnd 900°C (c).Fig. 6.X-ray powder diffraction patterns of ceramic sample RZH-2146 (a) and of the compo-site sample (b), both fired at 900°C for 3 hours.Received July 6, 1990Accepted September 20, 1990136 B. CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.s, XXIII125-138 (1990)15 100(°),CuKoćFigure 4B. CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.s., XXIII125-138 (1990) 13715 10G(°).CuKoCFigure 5138 B. CRNKOVIĆ-D. SLOVENEC-A. SOKAČ: Ceramics from Salona, VAMZ, 3.s, XXIII125-138 (1990)CGeGeK4x 10 cpsa20 15 100(°).CuKoCFigure 6

Ceramics from the Roman city of Salona near Split

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