Moroccan clay deposits: Physico-chemical properties in view of provenance studies on ancient ceramics

Applied Clay Science 172 (2019) 65–74

Contents lists available at ScienceDirect

Applied Clay Science journal homepage: www.elsevier.com/locate/clay

Research paper

Moroccan clay deposits: Physico-chemical properties in view of provenance studies on ancient ceramics

T

⁎

Meriam El Ouahabia, , Hicham El Boudour El Idrissia,b, Lahcen Daoudib, Mouhssin El Halima,b, Nathalie Fagela a UR Argile, Géochimie et Environnement sédimentaires (AGEs), Département de Géologie, Quartier Agora, Bâtiment B18, Allée du six Août, 14, Sart-Tilman, Université de Liège, B-4000, Belgium b Laboratoire de Géosciences et Environnement (LGSE), Département de Géologie, Faculté des Sciences et Techniques, Université Cadi Ayyad, BP 549 Marrakech, Morocco

A R T I C LE I N FO

A B S T R A C T

Keywords: Pottery Raw clayey materials Firing properties Medieval Reference samples Morocco

Features of clayey raw materials from most important traditional pottery centers in the vicinity of the main medieval sites in Morocco, and their fired products were investigated. Besides clay from the North of Morocco, the used raw material was illitic clays (10–100%) and smectite-rich clays (0–67%) with variable amount of kaolinite, quartz and feldspars. Chlorite was also present in a small amount. The main major oxides were Si2O, Al2O3 and CaO. The fired tests (800–1100 °C) displayed a decrease in open porosity of the sintered clay by raising the temperature, mainly from 1000 °C due to the inception of melting. This change was coupled with the change in mineralogical composition. New crystalline phases as Ca-silicates (diopside and gehlenite), hematite, spinel and mullite occurred during firing process, attesting to the inception of melting and were responsible for porosity reduction. Reference clays for pottery were established based on the clay mineralogy and chemical composition. The present study would help to answer some archeological questions concerning possible sourcing areas for archeological ceramics, to determine techniques for the production of artefacts, and then to interpret cultural influences. Furthermore, the obtained results will support the inception of development of a compositional database for Moroccan pottery.

1. Introduction

(Kilikoglou et al., 1998). Provenance studies try to establish whether ceramic was locally produced or imported, and if the latter, to identify the production centre and/or the source of the raw materials that were used (Mason and Keall, 1988; Hein et al., 2004; Mommsen and Sjöberg, 2007; Tite, 2008). A better understanding of provenance, production technology, nature and function of ancient ceramics, requires physico-chemical approach to better understand the used raw material, including clay and/or temper. Clay minerals are the plastic part of ceramics, consequently, changes in their chemistry will result obviously in different physical changes too. Therefore, the chemistry of clays can determine their interaction with water, their plastic properties, and their firing behaviour during the ceramic process. It can also help to decide whether there is a need to add more or less tempering material. So, knowing clay mineral composition is essential to understand the choice of clay material by potters. Chemical and mineralogical compositions make the best approach for provenance study, when the obtained results on shards are compared to reference samples (Tite, 2008). Reference

Studies of ceramics in archaeology help to reconstruct past human activities, in particular production technology, which can reflect social, economic, and political contexts of societies (Goffer, 1983; Tite, 2008). Furthermore, ceramic analysis performed in tableware and pottery containers used in the transportation of goods provides an understanding of trade patterns and then the economy of ancient society (Ben-Shlomo and Mommsen, 2018). Therefore, provenance of ceramic artefacts is hugely relevant for archaeologists, when production centers are identified. Production technology by ancient ceramists is still the main issue for archaeologists (Tite et al., 2001; Kiderlen et al., 2017; Frahm, 2018; Yu et al., 2018). The reconstruction of the production technology of ceramics involves determining, on the one hand, what raw materials were used and how they were prepared and, on the other hand, how the ceramics were formed, decorated, and fired (Garrigós and Fernández, 2016). Technological studies have primarily to determine pottery firing temperatures, mechanical and thermal properties

⁎

Corresponding author. E-mail address: [email protected] (M. El Ouahabi).

https://doi.org/10.1016/j.clay.2019.02.019 Received 19 September 2018; Received in revised form 18 December 2018; Accepted 20 February 2019 0169-1317/ © 2019 Elsevier B.V. All rights reserved.

Applied Clay Science 172 (2019) 65–74

M. El Ouahabi, et al.

1269–1465, taking Fes as capital. The Marinid Sultanate maintained important relations with the Christian kingdoms, of Aragon or France, but also with its co-religionists Nasrid in Granada, Ziyanid in Tlemcen, Hafsid in Tunis and Mamluk in Cairo (Abun-Nasr, 1987). Safi, Salé, Fes and Meknes are called imperial cities, which were historical capitals of different monarchs ruled throughout the medieval period in Morocco (Almoravid, Almohad, Marinid and Saadian). Safi (Asfi), situated in the western Morocco, on the Atlantic Ocean, was the harbor of the capital Marrakech during the rule of Almohad empire (12th century). Safi had direct relations with Andalusia thanks to the development of exchanges experienced by it harbor. Safi is known for utilitarian and decorative pottery manufacture, attested since the twelfth century (Fqiyah, 2015). Salé (Sala) is a coastal city situated beside the Atlantic Ocean and had an extraordinary development during the Almohad and Marinid periods. This is due mainly to its harbor, allowed its connection to Europe. Recent archeological excavations uncovered a medieval pottery district (Dar El Baroud), including pottery workshops dating back to the 12th century. This medieval site is considered as a witness to the ancestral know-how that has always marked Salé, from medieval times to the present day, such as the nearness current pottery center of Oulja. Fes and Meknes regions (Saddina) are situated in nortwest. Excavations show the predominance of a culinary and rustic Berber ceramics made by local calcareous clay, providing evidence of occupation from 12th to 14th centuries (Martínez Enamorado et al., 2014). The Northern coast region, in particular, the Oued Laou region is among the large medieval sites in the Mediterranean coast of Morocco, including various pottery workshops dated between 13th and 14th centuries (Bazzana and Montmessin, 1995). In the region lies the current women's pottery site (known as Fran Ali), which is situated close to a main medieval site of Targha. The Targha site was the main pottery village with several workshops during the Marinid and Almohad dynasties (13-14th centuries), which have persisted to date. The archeological sherds that were found are utilitarian ceramics, which display a strong similarity in typologies with southern Spain, in particular with Malaga (southern Spain) (Bazzana and Montmessin, 1995).

samples are generally the analyzed raw clay material collected from various clay deposits in the vicinity of pottery fabrics and the regionally available data (Renson et al., 2011; Hacıosmanoğlu et al., 2017). When there is the lack or scarcity of the established reference samples, the sourcing area for archeological ceramics based only on elementary concentrations and mineralogical composition performed on shards, is a complex exercise (Usman et al., 2005; Knappett et al., 2011; Nunes et al., 2013). In this case, the shards composition does not correspond in an easy manner to any one distinct raw material. It is then necessary to compare archeological ceramics with reference samples with a known origin. Hence the need for the regional and non-regional established clay reference samples is necessary to support provenance studies for archeological ceramics. The history of pottery in Morocco is intimately linked to that of Mediterranean. In fact, the Moroccan imperial and medieval northern coastal cities have been influential regions through history. From the twelfth through the sixteenth centuries, the Strait of Gibraltar and the Atlantic harbors, mainly Safi and Salé, are the passageway between the Africa and Europe (Redman, 2014). Therefore, goods, generally in ceramic containers, were exchanged between southern Maghreb (currently northern Africa) and southern Europe in the medieval period. To distinguish between imported and local ceramic artefacts in western Mediterranean region is still challenging for archaeologists due to a wide-ranging and diversified trade network during this glory period (e.g. Fantuzzi et al., 2016). In Morocco, the duality between the Amazigh heritage, on the one hand, and the Hispano-Moorish influence, on the other hand, is reflected in the techniques used, the motifs and patterns that were used to decorate pottery pieces (Graves, 2007). Artisanal pottery production is mostly implemented in imperial cities (Fes, Salé, Meknes, Safi and Marrakech) and in northern coastal region. Two kind of traditional ceramics are deciphered in Morocco. In northern region, in Fran Ali area, women manufacture dishes and jars in a traditional way, decorate them with a rudimentary brush and cook them in an excavation in open air or in a traditional furnace made of clay. These potteries are functional, extremely simple, and brilliant without glazing. Their forms resemble strangely those of Greek, Phoenician and Carthaginian productions. In the center of the country, the traditional ceramic activities is implemented in imperial cities (Fes, Safi, Meknes and Salé), and are the main Moroccan pottery centers, since 11–12 century until now. The pottery is always glazed and decorated. The manufacturing processes unique to these cities are differentiated by the raw material, the colours and patterns used. This study aims to establish some reference samples of traditional ceramics in Morocco. This will be helpful in archeological investigations, mainly in ceramic sourcing areas. These references samples will be used in Morocco but also in Mediterranean regions and will help to decipher between imported and local ceramics. A second aim of the study is to highlight some technological properties of traditional potteries in Morocco, which will be useful to understand the production technology of traditional ceramics.

3. Materials and methods 3.1. Materials The raw materials were collected from various sites in the vicinity of former medieval workshops of pottery manufacture. Specifically, clays were sampled from the clay deposits currently used by the potters in the main traditional pottery centers in Morocco. The used raw material was mainly marls belonging to Miocene and Pliocene deposits. The current exploitation is made in a traditional way, by digging tunnels to recover the raw material. The region of Fes, the Benjlik site (Fig. 1) is the only source of good quality raw material used by potters to manufacture traditional ceramic “zellige”. This site is located south of Ain Nokbi potter village. The extracted material has homogenous Miocene greenish grey sandy marls with a slight change in grain-size. In the area of Salé, potters of Oulja site use the Miocene yellow marls and Triassic red clay to manufacture utilitarian ceramics (Fig. 1).. The artisans from Safi pottery center exploit homogenous Cretaceous clays. In the northern east Morocco, in Fran Ali site, nearby reddish sandy clays belonging to Pliocene marls is used by female artisans to manufacture utilitarian potteries. Potters from Meknes site use also the yellow Miocene marls. Sampling was performed in the main clay deposits used by potters, according to the changes in clay facies and grain-size. The characterization of the raw material at all sites was carried out on thirteen samples as the following; two samples from Fes site (FE1 and FE2); two samples from Salé site (S1 and S2); one sample from Safi site (SA); two samples from Fran Ali site (FA1 and FA2) and six sample from Meknes site (MK1 to MK6) (Table 1).

2. Archeological background The Maghreb reached the pinnacle of its glory between the eleventh and the fifteenth centuries. During this period, successions of dynasties (Almoravid, Almohad and Marinid) have ruled over a large territory centered on Morocco, spanning over territories from North of Africa (Morocco, Algeria, Tunisia and Libya today) to Andalusia (Southern Spain). The Almoravid dynasty was the first empire between Africa and Spain (1049–147), and Marrakech was its capital. In the period 1147–269, the Almohad dynasty succeeded in overthrowing the ruling Almoravid dynasty. They then extended their power over all of the Maghreb, Andalusia and all of Islamic Iberia. The empire revolved around three capitals, namely Marrakech, Sevilla and Rabat (Buresi and El Aallaoui, 2012). The Marinid dynasty appeared in the period 66

Applied Clay Science 172 (2019) 65–74

M. El Ouahabi, et al.

Fig. 1. Geographical and geological situation of the study area including the main pottery sites. Study area showing geological map and sample locations. Table 1 Major chemical composition in oxides (wt%). < DL = below detection limit. Pottery site

Sample

Lithology

SiO2

Al2O3

CaO

Fe2O3

MgO

Na2O

K2 O

TiO2

P2O5

SO3

Fes

FE1 FE2 S1 S2 SA FA1 FA2 MK1 MK2 MK3 MK4 MK5 MK6

Miocene grey marl Miocene sandy marl Triassic red clay Miocene yellow marl Cretaceous red clay Pliocene yellow sandy marl Pliocene yellow-orange sandy marl Miocene grey marl Miocene yellow marl Miocene yellow marl Miocene yellow marl Miocene yellow marl Miocene yellow marl

51.8 57.3 54.8 36.8 52.4 53.7 58 44.9 42.7 41.3 43.1 41.6 43.1

15.4 12.3 15.6 9 17.4 26.6 25.4 24.8 24.8 21.0 22.7 24.2 24.1

17.9 17.9 10.2 38.4 6.4 0.5 0.4 14.2 12.2 15.6 13.2 15.1 12.4

5.2 4.9 12.2 7.1 12.3 12 10 5.1 5.7 3.7 4.5 11.9 4.7

3.5 3 1.4 2.9 2.2 1.4 1 2.7 2.3 2.7 2.4 1.9 2.6

1.3 1.2 0.4 0.3 0.5 0.5 0.7 0.8 0.8 0.8 0.8 0.7 0.9

2.2 1.8 3.2 2.9 6.8 4.2 3.6 4.1 4.1 3.4 3.7 3.7 3.8

0.8 0.6 1.4 1.1 1.6 1 0.9 0.8 0.8 0.7 0.7 0.7 0.7

0.8 0.4 0.3 0.2 0.2 < DL < DL 0.3 0.2 0.2 0.2 0.2 0.3

1.1 0.6 < DL 1.2 0.2 < DL < DL 0.2 0.1 0.4 0.1 < DL 0.5

Salé Safi Fran Ali Meknes

and fired samples was estimated based on the peak area to total diffractogram area using DIFFRACplus EVA software (Bruker). Bulk mineralogical quantification was based on the Rietveld method using TOPAS software (DIFFRACplus TOPAS Ver. 4.2.0.1, Bruker-AXS). For the clay fraction, the whole sediment was decarbonated with HCl (0.1 mol/L) and the < 2 μm fractions were separated by settling them in a water column. Samples were mounted as oriented aggregates on glass slides (Moore and Reynolds, 1997). For each sample three X-ray

3.2. Experimental procedure Mineralogical composition of raw materials and high temperature crystalline phases (after firing) was performed by X-ray diffraction using a Bruker D8-Advance diffractometer with Cu Kα radiations (scan step size: 0.02°; time/step: 0.6 s; anode: copper with Kα = 1.5418 Å) on powdered bulk sediment and on the < 2 μm fraction (Department of Geology, University of Liège). The % of amorphous phases of the raw 67

Applied Clay Science 172 (2019) 65–74

M. El Ouahabi, et al.

Fig. 2. Mineralogical composition of the bulk samples and clay fraction (< 2 μm) of the main Moroccan clays used for pottery.

Fig. 3. Grain-size characteristics of studied clay raw materials based on the sand–silt–clay ratios (Shepard, 1954) for the main clays used for Moroccan pottery manufacture.

68

Applied Clay Science 172 (2019) 65–74

M. El Ouahabi, et al.

(Casagrande, 1948). The Atterberg limits are routinely used for optimization of ceramic pastes (Marsigli and Dondi, 1997). These limits were determined according to ASTM Standard (ASTM D4318, 2005) in ArGEnCo Laboratory (University of Liege) as described by Casagrande (1948) and Andrade et al. (2011). Technological tests consisting of a simulation of the industrial process were performed on a laboratory scale. After drying, samples were ground by crushing (< 2 mm), and then each clay sample was wetted with distilled water to obtain homogeneous paste in order to achieve the proper plasticity for molding or shaping. The pieces (4 cmlong, 2 cm-wide and 2 cm-thick) were obtained by hand shaping and then dried in a shaded and ventilated room for 48 h. The dried samples (during 12 h at 105 °C in oven) were kiln-fired at different temperatures (800, 850, 900, 950, 1000, 1050, and 1100 °C) over 1 h. The water absorption capacity (WAC) was determined in fired clays pieces after each heating cycle, according to standard procedure (ASTM norm C373-72, 2006). 4. Results 4.1. Physico-chemical and mineralogical characteristics of raw materials 4.1.1. Mineralogical and chemical composition The bulk mineralogical composition of the samples was diversified (Fig. 2); it consisted principally of clay minerals (27–56%), quartz (12–27%), calcite (0–29%), dolomite (0–13%), K-feldspar (0–16%), and plagioclase (0–6%). The main differences between all samples were the content of clay mineral phases, carbonates and feldspars. Indeed, samples from Fes, Salé (S2) and Meknes mainly contained lower values of total clay (< 45%), while the remaining samples showed values between 45 and 67%. The samples from Fran Ali are non-calcareous at all, while the sample S1 from Salé and the sample from Safi exhibited values ≤10%. Other samples displayed calcite and dolomite amount between 22 and 33%. The contents of feldspars were ≤ 10% for most samples, except for S2 where the content was 20%. The raw clay materials used for pottery had a variable clay mineral composition, with illite (0–100%), smectite (0–67%), and kaolinite (0–45%) being the most abundant clay minerals (Fig. 2). All samples of Meknes have > 6% of chlorite which is a percentage higher than the rest of samples, except in Fran Ali. Illite/smectite mixed-layers were founded only in Fes and Salé clay materials but didn't exceed 3%. The chemical composition is consistent with the mineralogical composition. The most abundant oxides in the studied samples were SiO2 (36.8–58.0%), Al2O3 (9.0–26.6%), CaO (0.4–38.4%) and Fe2O3 (3.7–12.3%) (Table 1). SiO2 was the least abundant oxide in sample S2 (36.8%), while its content for the most of sample was between 41 and 58%. Al2O3 was most abundant in samples from Fran Ali and Meknes (> 20%). The samples from Fran Ali site (FA1 and FA2) contained almost traces of CaO, while its content in most samples exceeded 10% and reached the maximal value (38%) in sample S2.

Fig. 4. (a) Position of the studied clays on the Casagrand diagram. (b) Diagram of Bain and Highley (1979) showing the optimal domain for clay shaping by extrusion.

patterns were recorded: air-dried, ethylene-glycol solvated for 24 h, and heated at 500 °C for 4 h. The background noise of the X-ray patterns was removed, and the line position and intensity diffraction peak were calculated with DIFFRACplus EVA software (Bruker). Semi-quantitative estimations of the main clay species were obtained on EG runs according to the methods of Biscaye (1965) and Fagel et al. (2003). The chemical composition of major elements was determined by Xray fluorescence spectroscopy (XRF) on lithium–borate fused glass (Duchesne and Bologne, 2009) with a Panalytical Axios spectrometer equipped with Rh-tube, using argon-methane gas. Data handling was performed with the IQ+ software (University of Liège, Belgium). The grain size distribution allows to estimate the permeability of a clayey material, which constitutes an important property for ceramic paste during shaping process. Malvern Mastersizer 2000 (Department of Chemistry, University of Liège) was used to determine the particle size distribution of bulk sediment. About 1 g of sample was dispersed into a 100 mL deionized water tank free of additive dispersant, disaggregated with a 2000 rpm stirrer and by ultrasonic waves (10%). To avoid clay flocculation, 2 mL of 50 g/L of sodium hexametaphosphate was added for each grain size measurement. Grain-size classification for ceramists (sand fraction > 20 μm, silt fraction between 2 and 20 μm, clay fraction < 2 μm) was used. Evaluation of the plasticity of the clay materials was based on measurement of the Atterberg Limits, namely liquid limit (LL) and plastic limit (PL), from which the plasticity index (PI) was deduced

4.1.2. Grain-size distribution and plasticity behaviour The bulk samples showed wide variation in grain-size (Fig. 3), with the clay fraction ranging from 7 to 49%, silt fraction from 51 to 93%, and sand fraction from 0 to 18%. The samples from Fran Ali contained the lowest content of clay fraction (< 10%) and consequently the highest content of silt (> 90%). The highest content of clay fraction (~25%) was recorded for the most Meknes samples. Concerning the sand fraction, the highest content was recorded for sample FE2 from Fes, while the remaining samples had values < 5%. The liquid limit of studied samples ranged between 36 and 63% (Fig. 4), while plastic limit values were between 20 and 41%. The Plasticity indexes resulting ranged between 10 and 36. All studied samples had liquid limit values higher than 35% and then were 69

Applied Clay Science 172 (2019) 65–74

M. El Ouahabi, et al.

Fig. 5. Variation of water absorption capacity in terms of firing temperature (800–1100 °C) for fired specimens.

considered as medium to highly plastic according to Holtz and Kovacs (1981). The highest plastic samples (LL > 50%) were observed for S1, FE1, and MK samples.

5. Discussion

4.2. Firing characteristics

The clay mineralogical composition generally reflects the lithology of parental material and then provides information on weathering stage of rocks. In sedimentary rocks most clay minerals are detrital or neoformed and present a continuous evolution of their composition to reach a thermodynamic equilibrium according to the weathering conditions (Thorez, 1976). Illite and chlorite are primary minerals inherited from the parent rocks prone to weathering (Chamley, 1989). Smectite is generally considered as secondary minerals formed during chemical weathering (Righi and Meunier, 1995). Pliocene clays belonging to the northern Morocco and used by women potters are rich in illite, associated with a small amount of kaolinite. In the center of Morocco, the Miocene clays used for urban pottery are composed mainly of illite and kaolinite with small content of smectite, chlorite and illite/smectite mixed layers. Cretaceous clay from Safi area consists mostly of illite and kaolinite associated with traces of chlorite. The presence of smectite associated with mixed-layer phases in the Miocene clays is due to the transformation of illite into smectite as a result of the progressive removal of K+ ions from the interlayer (Sachsenhofer et al., 1998). Reported in most of the studied clays, kaolinite is associated with variable amounts of K-feldspars. Kaolinite is probably formed under a hydrolyzing climate by chemical weathering (neoformation or transformation) of feldspars (Chamley, 1989), such as that prevailing during most of the Cretaceous and Miocene (Chamley et al., 1979; Griffin, 2002). In light of the different processes that may have accounted for the presence of the different types of clay minerals in the study areas, there are the possible relationship between lithology of parent rock and mineralogy.

5.1. Clay mineralogy in relation to parental lithologies

4.2.1. Water absorption capacity Water absorption capacity (WAC) decreased with increasing firing temperature (800 to 1100 °C). At 800 °C, the WAC values ranged between 15 and 30% and decreased until 6 to 21% at 1100 °C (Fig. 5). The sample S2 and MK1 showed the highest values at low and high temperature, while the samples FE1 and FE2 indicated the lowest values at high temperature. 4.2.2. Mineralogical transformation during firing Overall, the first mineral modifications observed with increasing temperature included the dehydroxylation of kaolinite at temperatures below 550 °C (Table 2, Fig. 6). Dolomite, calcite, illite/smectite mixed layers, smectite and chlorite disappeared completely at temperature below 900 °C. Illite persisted even at temperature of 900 °C except for Meknes and Fes samples which disappeared between 550 and 900 °C. Concerning the transformed phases, from 900 °C, hematite appeared in all studied samples, while gehlenite appeared in all calcareous clays and diopside only appeared in samples with dolomite. An increase in diopside, gehlenite and hematite amounts with increasing temperature was observed. Spinel appeared at temperature of 900 °C only in Fran Ali, Salé (S1) and SA samples, its apparition was extended. Mullite was only observed in the sample SA from 1000 °C. Feldspars increased their abundance from 1000 °C for the majority of samples, except for sample S1 and Fran Ali clays. However, quartz content tended to decrease sharply at 1100 °C with less significant variation for FE1, SA and MK5 samples (Table 2). 70

Applied Clay Science 172 (2019) 65–74

M. El Ouahabi, et al.

Table 2 Mineral modification during firing. Amorphous (%)

Unfired clays FE1 25 FE2 30 S1 37 S2 13 SA 41 FA1 31 FA2 38 MK1 32 MK2 35 MK3 31 MK4 33 MK5 35 MK6 29 Fired at 800 °C FE1 25 FE2 29 S1 37 S2 7 SA 37 FA1 30 FA2 36 MK1 33 MK2 35 MK3 31 MK4 33 MK5 31 MK6 29 Fired at 900 °C FE1 20 FE2 25 S1 39 S2 7 SA 36 FA1 35 FA2 36 MK1 35 MK2 39 MK3 39 MK4 36 MK5 39 MK6 33 Fired at 1000 °C FE1 24 FE2 20 S1 28 S2 8 SA 44 FA1 40 FA2 40 MK1 41 MK2 35 MK3 31 MK4 36 MK5 35 MK6 32 Fired at 1100 °C FE1 24 FE2 21 S1 15 S2 8 SA 44 FA1 37 FA2 36 MK1 37 MK2 32 MK3 36 MK4 27 MK5 32 MK6 28

Raw mineralogical phases (%)

Transformed phases

Total Clay

Q

Dol

Cal

Kfs

Pl

Kaol

Sm

Ch

I

I-Sm

GOF

Mu

Sp

Di

Gh

Hem

38 42 51 33 67 60 54 42 50 37 43 34 44

19 21 26 15 15 12 19 27 22 25 19 21 20

13 6 0 7 5 0 0 3 2 4 3 2 3

15 16 8 22 3 0 0 22 21 29 26 29 20

3 6 4 16 3 2 2 2 2 2 4 2 3

3 4 4 4 2 3 6 2 1 0 0 0 5

13 13 6 6 21 0 5 13 11 12 11 6 13

3 5 4 3 0 0 0 11 14 13 14 8 14

3 4 3 2 4 0 0 10 18 6 11 9 9

11 15 29 19 30 27 27 5 4 4 4 3 4

3 2 3 1 0 0 0 0 0 0 0 0 0

2.85 2.90 3.31 3.48 2.44 2.46 2.44 2.48 2.27 2.80 2.89 2.80 2.82

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++

++ + − + + − − + + + + + +

+ + + + + − − ++ + ++ ++ ++ +

+ + + ++ + + + + + + + + +

+ + + + + + + + + − − − +

− − − − − − − − − − − − −

+ + + + − − − + + + + + +

+ + + + + − − + + + + + +

++ ++ +++ +++ +++ +++ +++ + + + + + +

+ + + + − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++

− − − − − − − − − − − − −

− − − − − − − − − − − − −

+ + + ++ ++ + + ++ ++ ++ ++ ++ ++

+ + + + + + + − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − + + + + + − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − + − + + + − − − − − −

+ + − + + − − + + + + + +

+ + + + + − − + + + + + +

+ + + + + + + + + + + + +

++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++

− − − − − − − − − − − − −

− − − − − − − − − − − − −

++ ++ + ++ ++ + + ++ ++ ++ ++ ++ ++

+ + + + + + + − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − + − − − − − − − −

− − + + + + + + − + − − +

+ + − + + − − ++ ++ ++ ++ + +

+ + + + + − − ++ ++ ++ ++ ++ ++

+ + + ++ ++ + + + + + + ++ +

++ + + + ++ + + + + + + ++ +

− − − − − − − − − − − − −

− − − − − − − − − − − − −

++ ++ + ++ ++ + + ++ ++ ++ ++ ++ ++

+ + + + + + + − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − − − − − − − − − −

− − − − + − − − − − − − −

+ + + ++ + + + + + ++ ++ ++ ++

++ ++ − ++ + − − ++ ++ + + + +

+ + + ++ + − − ++ ++ + ++ + +

++ ++ + ++ ++ + + + + + + ++ +

Q: Quartz, Dol: Dolomite, Cal: Calcite, Kfs: K-Feldspar, Pl: Plagioclase, Kaol: Kaolinite, Sm: Smectite, I: Illite, I/Sm: Illite/smectite mixed layers, Mu: Mullite, Sp: Spinel, Di: Diopside, Gh: Gehlenite, Hem: Hematite, GOF: goodness of fit. (+++) very abundant, (++) abundant, (+) scarce, (−) not detected. 71

Applied Clay Science 172 (2019) 65–74

M. El Ouahabi, et al.

Fig. 6. Diffraction patterns of heated sample FE2 up to 1100 °C. Q: Quartz, Dol: Dolomite, Cal: Calcite, Kfs: K-Feldspar, Pl: Plagioclase; T-Clay: Total clay, Sm: Smectite; Ch: chlorite; Kaol: Kaolinite, I: Illite, Di: Diopside, Gh: Gehlenite, Sp: Spinel, Hem: Hematite.

Illite, which is also one of the major component of the studied clays, is widely used as a fluxing material in traditional ceramics for the production of cooking pots, plates, tiles, bricks and stoneware tiles (Ferrari and Gualtieri, 2006). In addition, chlorite gives a red colour to bricks during firing. The chlorite-rich samples will therefore have an aesthetic appearance after firing due their iron content. Finally, the smectite increases the moisture content due to swelling and will provide greater plasticity to the ceramic articles during paste forming. In pottery, plasticity is usually viewed as the property or ability of a clay to be deformed and to retain the shape permanently without fracture (Moore, 1963;. Reed, 1995; Maritan et al., 2006). Clays with PI values lower than 10% are not appropriate for building-related ceramic production due to the risk of cracks during the extrusion process (Abajo, 2000). This problem is related to the short plastic interval. Most the studied clays have PI values higher than 10, so they have an adequate plastic behaviour allowing to prevent cracks during shaping (Dondi et al., 1998). As an exception, the samples from Meknes and S1 are characterized by higher linear shrinkage (Fig. 4b), so the risk of

5.2. Pottery properties The fine grained materials are the most suitable for the production of porous wares (Murray, 2007; Strazzera et al., 1997). The occurrence of calcium carbonate minerals in raw materials used in pottery may cause technological problems (e.g. white nodule and cracks). In particular, the decomposition of carbonates in clayey matrices at 800–900 °C yields Ca-bearing silicates, but this decomposition depends also on other factors such as grain-size, kiln atmosphere, and firing/cooling duration (Riccardi et al., 1999; Cultrone et al., 2001; Miras et al., 2018). Therefore, the presence of a significant quantity of carbonates in most of clay samples used for pottery manufacturing allows to increase the porosity when CO2 escapes during firing. The relative abundance of clay minerals may significantly influence the final properties of ceramic products. The studied clays are rich in illite, smectite and kaolinite, which are the most widely used as raw clay minerals in pottery. Kaolinite is used extensively because of its high fusion temperature and white colour characteristics after firing. 72

Applied Clay Science 172 (2019) 65–74

M. El Ouahabi, et al.

diopside and anorthite, rather than mullite (Trindade et al., 2009; Trindade et al., 2010). The correlation of chemical and mineralogical content of the studied raw clay used for traditional pottery making in Morocco is shown in Fig. 7. The clays used are mostly illitic or smectite-rich clays with variable amount of kaolinite (Figs. 2 and 7). Though the total of alkali and alkaline earth oxides expressed by the Fe2O3 + CaO + MgO/Al2O3 and Na2O + K2O/Al2O3 ratios, indicate that studied clays used for Moroccan pottery are composed of variable amount of CaO and Fe2O3, but not exceed 17% and 12% respectively, as medieval reference samples pottery established in southern Italy (Grifa et al., 2009; De Bonis et al., 2014), except for S2 (CaO, 34%). The variable amount of Fe2O3 for the studied clays gives dark-firing bodies and improves the green bending strength. Nerveless, elevated values of CaO for the most of Moroccan clays may turn the colour to yellowish or pinkish shades (Dondi et al., 2014). In the light of different raw clays used for the most important pottery sites in Morocco, our results will support the establishing reference groups of Moroccan traditional ceramics. Furthermore, such study could help to answer some archeological questions concerning possible sourcing, areas. This can also help to determine techniques for the production of artefacts and then possible interpretation of cultural influences. With the determination of the chemical and mineralogical composition of ceramic shreds, therefore, it will then be possible to relate it to a specific clay source and conditions of production, namely the firing temperature. Therefore, this study might be useful in supporting provenance studies of archeological ceramic.

Fig. 7. Relationships between chemical and mineralogical variations of the studied samples.

cracking cannot be excluded (Bain and Highley, 1979). The capacity of water absorption (WAC) decreases with firing temperature. A marked decrease in WAC values from 1000 °C occurred for most of our samples. Such observation may be explained by the reduction of the open porosity in relation with the formation of glassy phases as spinel and mullite, confirmed by XRD results (Table 2, Fig. 6). Overall, all clays used for pottery display a high WAC values (10–20%) from 1100 °C but remain consistent with the standards values for porous bodies which are always glazed (e.g. Dondi et al., 2014). Clays from the site of Fes, in particular, indicated the lowest WAC values (6%) due to the presence of fusible substances, yielding the formation of liquid phases and then the reduction of the open porosity. This is mainly demonstrated by spinel formation from 1100 °C for those samples, which enhance the vitrification of ceramic bodies and improve their mechanical strength. The WAC values are reduced when the calcareous phases (calcite and dolomite) are lacking, implying that sufficient amount of CaO (> 0.5%) plays an important role in the porosity reduction during firing (Fig. 5). Dagounaki et al. (2008) attested that carbonates play a complex role during firing, leading to the formation of a small-sized porosity. The new mineral phases such as feldspars and spinel control thermal and moisture expansion and are responsible for the production of sintered specimens. Chemical data are useful to predict the transformed phases during firing, but these changes are still challenging. This is due to a complex relationship between structural and chemical properties of the fired ceramics. Non-calcareous Pliocene clays, during firing, are eventually transformed into glassy phases (spinel and mullite) from 900 °C, required for the strength of the pottery bodies (Table 2). Mullite is derived from the Al content, which is related to the presence of clay mineral phases (mainly illite) and mica-rich minerals (e.g. Khalfaoui and Hajjaji, 2009; El Ouahabi et al., 2015; Laita and Bauluz, 2018). Melting is partial and ongoing until 1100 °C, attested by increases in spinel, feldspars, mullite and hematite, and in turn by the sharp drop in quartz content. In the calcareous Miocene, Cretaceous and Triassic clays, the presence of CaO prevents the formation of the mullite (Trindade et al., 2009; Trindade et al., 2010; El Ouahabi et al., 2015). Decomposed clay minerals form, in combination with CaO, phases such as gehlenite,

6. Conclusions Raw clay materials used for the most important traditional pottery sites from Morocco and their fired products were investigated. Diversified clays are exploited to manufacture pottery, mainly Pliocene sandy marl in the north, and Miocene and Cretaceous clays in the other sites. Raw clays can be considered as illitic clays (10–100%) and smectite-rich clays (0–67%) with variable amount of kaolinite, quartz, feldspars and small content of chlorite. Calcareous phases are variable content of calcite (0–29%) and small amount of dolomite. Physical parameters show that the raw materials are silty clays with medium to high plasticity. Fired specimens were produced and fired from 800 to 1100 °C in order to highlight the processing technique in the production of ceramic products from raw materials. A marked decrease in water absorption capacity values from 1000 °C occurred in the majority of the samples due to the reduction of the open porosity linked to the formation of glassy phases as spinel and mullite which is confirmed by XRD results. According to clay mineralogy and chemical composition, the clay materials used for the studied Moroccan traditional pottery display some similarity to references groups for medieval ceramics in southern Italy. The results of our study constitute a useful tool for archeological ceramic provenance investigations by supporting the development of reference groups of traditional ceramics from Moroccan sites, which may extend to the Mediterranean area. Acknowledgments Anonymous referee are thanked for their valuable comments and suggestions which greatly improved the paper. Thanks are also due to Editor Emilio Galan for constructive comments and editorial handling. References Abajo, M.F., 2000. Manual sobre fabricación de baldosas, tejas y ladrillos. 2000 Laboratorio Técnico Cerámico, Igualada, España, Beralmar. Abun-Nasr, J.M. (Ed.), 1987. A History of the Maghrib in the Islamic Period. Cambridge University Press, New York, pp. 455.

73

Applied Clay Science 172 (2019) 65–74

M. El Ouahabi, et al.

Age Greek Bronze Tripod Cauldrons: first evidence from neutron activation analysis of casting ceramics. Geoarchaeology 32, 321–342. Kilikoglou, V., Vekinis, G., Maniatis, Y., Day, P.M., 1998. Mechanical performance of quartz-tempered ceramics: part I, strength and toughness. Archaeometry 40, 261–279. Knappett, C., Pirrie, D., Power, M.R., Nikolakopoulou, I., Hilditch, J., Rollinson, G.K., 2011. Mineralogical analysis and provenancing of ancient ceramics using automated SEM-EDS analysis (QEMSCAN®): a pilot study on LB I pottery from Akrotiri, Thera. J. Archaeol. Sci. 38, 219–232. Laita, E., Bauluz, B., 2018. Mineral and textural transformations in aluminium-rich clays during ceramic firing. Appl. Clay Sci. 152, 284–294. Maritan, L., Nodari, L., Mazzoli, C., Milano, A., Russo, U., 2006. Influence of firing conditions on ceramic products: experimental study on clay rich in organic matter. Appl. Clay Sci. 31, 1–15. Marsigli, M., Dondi, M., 1997. Plasticità delle argille italiane per laterizi e previsione del loro comportamento in foggiatura. L'Industria dei Laterizi 46, 214–222. Martínez Enamorado, V., Gutiérrez López, J.M., Iglesias, L., 2014. L'iqlīm Ṣaddīna d'alAndalus, aproche historiographique et archéologique. In: Akdim, B., Lazarev, G., Enamorado, V. Martínez (Eds.), Le pays des Ṣaddīna. Une étude géographique, historique et archéologique des sites de Ṣaddīna, villes médiévales du Maroc et de l'Andalousie. Villes et sites archéologiques du Maroc, Ministère de la Culture-INSAP, Royaume du Maroc, Rabat, pp. 83–118. Mason, R.B., Keall, E.J., 1988. Provenance of local ceramic industry and the characterization of imports: petrography of pottery from medieval Yemen. Antiquity 62, 452–463. Miras, A., Galán, E., González, I., Romero-Baena, A., Martín, D., 2018. Mineralogical evolution of ceramic clays during heating. An ex/in situ X-ray diffraction method comparison study. Appl. Clay Sci. 161, 176–183. Mommsen, H., Sjöberg, B.L., 2007. The importance of the ‘best relative fit factor when evaluating elemental concentration data of pottery demonstrated with Mycenaean sherds from Sinda, Cyprus. Archaeometry 49, 359–371. Moore, F., 1963. Two instruments for studying the plasticity of clays. J. Sci. Instr. 40, 228–231. Moore, D.M., Reynolds, R.C., 1997. X-ray Diffraction and the Identification and Analysis of Clay Minerals. Oxford University Press, New York, pp. 253. Murray, H., 2007. Applied clay mineralogy: occurrences, processing and applications of kaolins, bentonites, palygorskite sepiolite, and common clays. In: Developments in Clay Science. vol. 2 Elsevier, Amsterdam. Nunes, K.P., Toyota, R.G., Oliveira, P.M.S., Neves, E.G., Soares, E.A.A., Munita, C.S., 2013. Preliminary compositional evidence of provenance of ceramics from Hatahara archaeological site, central Amazonia. J. Chem. 2013. Redman, C.L., 2014. Qsar Es-Seghir: An Archaeological View of Medieval Life. Academic Press, Florida, pp. 255. Reed, J., 1995. In: Reed, J.S. (Ed.), Principles of Ceramics Processing. J. Wiley and Sons, New York, pp. 450. Renson, V., Coenaerts, J., Nys, K., Mattielli, N., Vanhaecke, F., Fagel, N., Claeys, P., 2011. Lead isotopic analysis for the identification of Late Bronze Age pottery from Hala Sultan Tekke, Cyprus. Archaeometry 53, 37–57. Riccardi, M., Messiga, B., Duminuco, P., 1999. An approach to the dynamics of clay firing. Appl. Clay Sci. 15, 393–409. Righi, R., Meunier, A., 1995. Origin of clays by rock weathering and soil formation. In: Velde, B. (Ed.), Origin and Mineralogy of Clays. Springer, Berlin, Heidelberg, pp. 43–161. Sachsenhofer, R.F., Rantitsch, G., Hasenhüttl, C., Russegger, B., 1998. Smectite to illite diagenesis in early Miocene sediments from the hyperthermal western Pannonian Basin. Clay Miner. 33, 523–537. Shepard, F.P., 1954. Nomenclature based on sand-silt-clay ratios. J. Sediment. Res. 24, 151–158. Strazzera, B., Dondi, M., Marsigli, M., 1997. Composition and ceramic properties of tertiary clays from southern Sardinia, Italy. Appl. Clay Sci. 12, 247–266. Thorez, J., 1976. In: Lelotte, G. (Ed.), Practical Identification of Clay Minerals. Liège, pp. 90. Tite, M.S., 2008. Ceramic production, provenance and use-a review. Archaeometry 50, 216–231. Tite, M.S., Kilikoglou, V., Vekinis, G., 2001. Strength, toughness and thermal shock resistance of ancient ceramics, and their influence on technological choice. Archaeometry 43, 301–324. Trindade, M., Dias, M., Coroado, J., Rocha, F., 2009. Mineralogical transformations of calcareous rich clays with firing: a comparative study between calcite and dolomite rich clays from Algarve, Portugal. Appl. Clay Sci. 42, 345–355. Trindade, M., Dias, M., Coroado, J., 2010. Firing tests on clay-rich raw materials from the Algarve basin (southern Portugal): study of mineral transformations with temperature. Clay Clay Miner. 58, 188–204. Usman, A.A., Speakman, R.J., Glascock, M.D., 2005. An initial assessment of prehistoric ceramic production and exchange in northern Yoruba, north central Nigeria: results of ceramic compositional analysis. Afr. Archaeol. Rev. 22, 141–168. Yu, Y.B., Huang, F.C., Cui, J.F., Guo, C.J., Chen, J.L., 2018. The chemical composition and production area of early western Zhou Proto-porcelain unearthed from Vejiashan cemetery, Suizhou, China. Archaeometry 60, 19–32.

Andrade, F.A., Al-Qureshi, H.A., Hotza, D., 2011. Measuring the plasticity of clays: a review. Appl. Clay Sci. 51, 1–7. ASTM Standard C373-72, ASTM, Philadelphia, PA, 2006. Standard Test Method for Water Absorption, Bulk Density, Apparent Porosity, and Apparent Specific Gravity of Fired Whiteware Products. ASTM Standard D4318, 2005. Standard Test Methods for Liquid Limit Plastic Limit, and Plasticity Index of Soils. Bain, J.A., Highley, D.E., 1979. Regional appraisal of clay resources-a challenge to the clay mineralogist. Dev. Sedimentol. 27, 437–446. Bazzana, A., Montmessin, Y., 1995. Quelques aspects de la céramique médiévale du Maroc du Nord, In Actes du 5ème Colloque sur la Céramique Médiévale en Méditerranée Occidentale, pp. 241-259. Ben-Shlomo, D., Mommsen, H., 2018. Pottery production in Jerum during the Iron Age: a new compositional profiling. Geoarchaeology 33, 349–363. Biscaye, P.E., 1965. Mineralogy and sedimentation of recent deep-sea clay in the Atlantic Ocean and adjacent seas and oceans. Bull. Geol. Soc. Am. 8, 803–832. Buresi, P., El Aallaoui, H. (Eds.), 2012. Governing the Empire: Provincial Administration in the Almohad Caliphate (1224-1269): Critical Edition, Translation, and Study of Manuscript 4752 of the Hasaniyya Library in Rabat Containing 77 Taqādīm (appointments). vol. 3. Brill, Leiden, Netherland, pp. 450. Casagrande, A., 1948. Classification and Identification of Soils. Trans. Am. Soc. Civ. Eng. 113, 901–930. Chamley, H., 1989. Clay Sedimentology. Springer-Verlag, Berlin, pp. 623. Chamley, H., Debrabant, P., Foulon, J., d'Argoud, G.G., Latouche, C., Maillet, N., Maillot, H., Sommer, F., 1979. Mineralogy and geochemistry of Cretaceous and Cenozoic Atlantic sediments off the Iberian Peninsula, Site 398, DSDP Leg 47B. Init. Repts. DSDP 47, 429–449. Cultrone, G., Rodriguez-Navarro, C., Sebastian, E., Cazalla, O., De La Torre, M.J., 2001. Carbonate and silicate phase reactions during ceramic firing. Eur. J. Mineral. 13, 621–634. Dagounaki, C., Sikalidis, C., Kassoli-Fournaraki, A., Tsirambides, A., 2008. The influence of carbonates on the technological properties of an industrial red clay. Ind. Ceram. 28, 181–187. De Bonis, A., Cultrone, G., Grifa, C., Langella, A., Morra, V., 2014. Clays from the Bay of Naples (Italy): New insight on ancient and traditional ceramics. J. Eur. Ceram. Soc. 34, 3229–3244. Dondi, M., Marsigli, M., Venturi, I., 1998. Technological requirements of raw materials for heavy clay products. In: Proceedings of the 2nd Mediterranean Clay Meeting, Aveiro, Portugal. Vol. 2. Dondi, M., Raimondo, M., Zanelli, C., 2014. Clays and bodies for ceramic tiles: Reappraisal and technological classification. Appl. Clay Sci. 96, 91–109. Duchesne, J.C., Bologne, G., 2009. XRF major and trace element determination in Fe–Ti oxide minerals. Geol. Belg. 12, 205–212. El Ouahabi, M., Daoudi, L., Hatert, F., Fagel, N., 2015. Modified mineral phases during clay ceramic firing. Clay Clay Miner. 63, 404–413. Fagel, N., Boski, T., Likhoshway, L., Oberhaensli, H., 2003. Late Quaternary clay mineral record in Central Lake Baikal, Academician Ridge (Siberia). Palaeogeogr. Palaeoclimatol. Palaeoecol. 193, 159–179. Fantuzzi, L., Ontiveros, C., Aquilué, X., 2016. Archaeometric characterization of amphorae from the late antique city of Emporiae, Catalonia, Spain. Archaeometry 58, 1–22. Ferrari, S., Gualtieri, A., 2006. The use of illitic clays in the production of stoneware tile ceramics. Appl. Clay Sci. 32, 73–81. Fqiyah, R., 2015. La valorisation du Musée national de la céramique de Safi: La médiation patrimoniale comme une possibilité de valorisation. Éditions universitaires européennes. Frahm, E., 2018. Ceramic studies using portable XRF: from experimental tempered ceramics to imports and imitations at tell Mozan, Syria. J. Archaeol. Sci. 90, 12–38. Garrigós, J.B., Fernández, M.M., 2016. Designing rigorous research. In: Hunt, Alice M.W. (Ed.), The Oxford Handbook of Archaeological Ceramic Analysis, pp. 19–47. Goffer, Z., 1983. Physical studies of archaeological materials. Rep. Prog. Phys. 46, 1193–1983. Graves, M.S., 2007. A certain barbaric originality: Moroccan Pottery as Viewed by British Travel Writers of the Nineteenth Century. J. North Afr. Stud. 12, 501–516. Grifa, C., Morra, V., Langella, A., Munzi, P., 2009. Byzantine ceramic production from Cuma (Campi Flegrei, Napoli). Archaeometry 51, 75–94. Griffin, D.L., 2002. Aridity and humidity: two aspects of the late Miocene climate of North Africa and the Mediterranean. Palaeogeogr. Palaeoclimatol. Palaeoecol. 182, 65–91. Hacıosmanoğlu, S., Kİbaroğlu, M., Sunal, G., Kozal, E., Gutsuz, P., 2017. Geochemical and Petrographic Analysis of Late Bronze Age Cypriot Ceramics (White Slip I and II and Monochrome) from Tell Atchana/Alalakh (Hatay) in the Amuq Valley. Archaeometry 60, 471–488. Hein, A., Mommsen, H., Zender, G., 2004. Pliocene clays from Aegina (Greece): Reference material for chemical provenance studies on Bronze Age pottery from the Island. Geoarchaeology 19, 553–564. Holtz, R.D., Kovacs, W.D., 1981. An Introduction to Geotechnical Engineering. Prentice Hall, New Jersey, pp. 733. Khalfaoui, A., Hajjaji, M., 2009. A Chloritic-illitic clay from Morocco: Temperature-timetransformation and neoformation. Appl. Clay Sci. 45, 83–89. Kiderlen, M., Hein, A., Mommsen, H., Müller, N.S., 2017. Production sites of early Iron

74