Egyptian faience

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Egyptian faience is a non-clay ceramic displaying surface vitrification which creates a bright blue-green luster. It is called 'Egyptian faience' to distinguish it from Faience which refers to the ambiguous term frit and a type of pottery now know as majolica: a tin glazed ware originally produced in Faenza in northern Italy.^[1] Egyptian faience, both locally produced and exported from Egypt, occurs widely in the ancient world, and is well known from Mesopotamia, the Mediterranean and in northern Europe as far away as Scotland. ^{[1] [2]}

Contents 1 Introduction 2 Faience Working Technology 3 Glazing technology 4 Recognition of glazing techniques 5 Typologies 6 Workshop evidence 7 Notes 8 References

[edit] Introduction

From the inception of faience in the archaeological record of Ancient Egypt, the elected colors of the glazes varied within an array of blue-green hues. Glazed in these colors, faience was perceived as substitute for blue-green materials such as turquoise, found in the Sinai peninsula, and lapis lazuli, from Afghanistan.^[1]. As early as the Predynastic graves at Naqada, Badar,el-Amrah, Matmar, Harageh, Avadiyedh and El-Gerzeh, glazed steatite and faience beads are found associated with these semi-precious stones.^[3] The association of faience with turquoise and lapis lazuli becomes even more conspicuous in Quennou's funerary papyrus, giving his title as the director of overseer of faience-making, using the word which strictly means lapis lazuli, which by the New Kingdom had also come to refer to the 'substitute', faience .^[1] The symbolism embedded in blue glazing could recall both the Nile, the waters of heaven and the home of the gods. Whereas green, could possibly evoke images of regeneration, rebirth and vegetation.^[4]

Relationship with Egyptian Copper industry

The discovery of faience glazing has tentatively been associated with the copper industry: bronze scale and corrosion products of leaded copper objects are found in the manufacture of faience pigments.^[5] However, although the likelihood of glazed quartz pebbles developing accidentally in traces in copper smelting furnaces from the copper and wood ash is high, the regions in which these processes originate do not coincide.^[6]

Relationship with Egyptian Glass industry

Although it appears no glass was intentionally produced in Egypt prior to the 18th dynasty, it is likely that faience, frit and glass were all made in close proximity or in the same workshop complex, seeing as developments in one industry are reflected in others.^[3]. Such close relationship is reflected in the prominent similarity of the formulations of faience glaze and contemporary glass compositions. ^[5] Despite the differences in the pyrotechnology of glass and faience, the latter being worked cold, archaeological evidence suggests that New Kingdom glass and faience production was undertaken in the same workshops.^[1]

Typical Composition and Access to Raw Materials

Faience has been defined as the first high technology ceramic, to emphasize its status as an artificial medium, rendering it effectively a precious stone.^[7] Egyptian faience is a non-clay ceramic composed of crushed quartz or sand, with small amounts of calcite lime and a mixture of alkalis, displaying surface vitrification due to the soda lime silica glaze often composed of copper pigments to create a bright blue-green luster.^[1] While in most instances domestic ores seem to have provided the bulk of the mineral pigments, evidence suggests that during periods of prosperity raw materials also available locally, such as lead and copper, were imported.^[5] Plant ash, from halophitic plants typical of dry and sea areas, was the major source of alkali until the Ptolemaic Period, when natron based alkalis almost completely replaced the previous source.^[7] Although the chemical composition of faience materials varies over time and according to the status of the workshop, also as a cause of change of accessibility of raw materials, the material constitution of the glaze is at all times consistent with the generally accepted version of faience glazing.^[5]

[edit] Faience Working Technology

Typical faience mixture is thixotropic, that is thick at first and then soft and flowing as it begins to be formed.^[8] This property, together with the angularity of silica particles accounts for the gritty slumps formed when the material is wetted, rendering faience a difficult material to hold a shape.^[9] If pressed too vigorously this material will resist flow until it yields and cracks, as a cause of its limited plastic deformation and low yield strength.^[7]

Body Binding Technology

A number of possible binding agents, amongst arabic gum, clay, lime, egg white and resin, have been suggested to help in the binding process.^[10] Although traces of clay have been found in most Pharaonic faience, reconstruction experiments showed that clay, organic gums or lime while successfully improving the wet working performance, failed to improve the fired strength of the faience, or proved the gum was too sticky for the removal of objects from their molds ^[1][7][10] The use of alkalis as binders, in the form of natron or plant ash, produced suitable results in experiments.^[1] Pulverized glass or sintered material of similar composition could also enhance the fired strength of faience bodies: the compositions of such glasses is in fact comparable to the published compositions of New Kingdom glass. ^[5][11]

Body working technology

Three methods have been hypothesized to shape the body of faience objects: modeling, moulding and abrasion, the last being used in the conjunction with the first two.^[1] Modeling, scraping and grinding are the techniques most widely used in earlier times, as represented in the material qualities of Predynastic and Protodynastic faience objects.^[3] Predynastic bead manufacture is essentially a cold technology, more akin to stone working than glass: a general form of faience is modeled, possibly free formed by hand, then holes are drilled to create beads.^[3]

In the Middle Kingdom, the techniques employed are molding and forming on a core, sometimes in conjunction with intermediate layers between the glaze and the body.^[7] Marbleized faience, resulting from the working of different colored faience bodies together, as to produce a uniform adherent body, also appears in this period.^[7][5] Towards the end of the Middle Kingdom, incising, inlaying and resisting techniques appear: bound to become progressively popular towards the New Kingdom.^[7]. In the New Kingdom, beads, amulets and finger rings are produced by a combination of modeling and molding techniques.^[7]. In this period, sculptural detail was created using inlays of different colored faience or by scraping the body to reveal the white intermediate layer in relief.^[7]. Moulding was first applied to faience manufacture in the Middle Kingdom by forming a model of an object, or employing a finished faience piece, impressing it in wet clay, and later by firing the clay to create a durable mold.^[3][12] . The faience paste could then be pressed into the mold, and following drying, be re-worked through surface abrasion before firing.^[3]. Moulds could facilitate mass production of faience objects such as amulets rings and inlays, as evidenced by the several thousand of small open face, earth-ware clay molds excavated at Tell el Amarna.^[6] Wheel throwing, possibly occurring from the New Kingdom onwards, is certainly established by the Greco-Romano period, when large amounts of clay seems to have been added to the faience body.^[3]. Because of the limited plasticity of faience, rendering throwing extremely difficult, a progressive increase of clay in the faience bodies culminating in the quartz, clay and glass frit bodies of Islamic times, is observed in the archaeological record.^[7][13]. Ptolemaic and Roman faience tends to be typologically and technologically distinct from the earlier material: it is characterized by the widespread use of moulding and high relief on vessels.^[14]

[edit] Glazing technology

The technology of glazing a siliceous body with a soda lime silica glaze, employs various methods discovered over time: namely application, efflorescence and cementation glazing.

Application glazing

In the application method, formerly assumed to be the only one used for faience glazing; silica, lime and alkalis are ground in the raw state to a small particle size, thus mixed in water to form a slurry which is then applied to the quartz core.^[3][6][10] Partial fritting of the slurry favors the first stages of vitrification, which in turn lowers the final firing temperature. The slurry can be then applied to the body, through brushing or dipping, to create a fine, powdery coating.^[7] Upon firing, the water from the melting glaze partially diffuses in the sand body, sintering the quartz particles and thus creating some solid bridges in the body.^[7]

Efflorescence of glazing

In the self-glazing process of efflorescence, the glazing materials, in the form of water-soluble alkali salts, are mixed with the raw crushed quartz of the core of the object ^[8][9][15]. As the water in the body evaporates, the salts migrate to the surface of the object to recrystallize, creating a thin surface, which glazes upon firing.^[7]

Cementation glazing

Cementation glazing, a technique discovered in the Middle Kingdom, is also a self-glazing technique.^[3]. The possibility of the existence of cementation glazing, also known as 'Qom technique', followed the observation of this method in use at the village of 'Qom' in Iran in the 1960's.^[16] In this method the artefact, while buried in a glazing powder with a high flux content, is heated inside a vessel, causing the fusion of the object with the cement. During firing, the flux migrates to the quartz and precipitates as glass.^[16] Alternative techniques

A vapour glaze reaction similar to salt glazing is an alternative glazing process, has been suggested. In this process, the vaporization or dissociation of salts leads to vapour transport through the enveloping powder to the quartz body where a glaze is formed.^[17]

[edit] Recognition of glazing techniques

Although glaze compositions vary regionally and chronologically, depending on the formation of the body and the glazing process employed, objects produced with different glazing techniques do not exhibit immediate diagnostic chemical variations in their compositions.^[5][18]The recognition of the various glazing techniques, through microscopic observations of the degree of sintering and the vitreous phase of quartz body, is also ambiguous. For instance, objects with applied glazes and those which may have been glazed by efflorescence have overlapping characteristic features.^{[19] [5]} The following proposed criteria are subject to variation caused by increases in flux concentration, firing temperatures and time at peak temperatures.^[7]

Recognition of application glazing- Macroscopically, applied glazes vary in thickness through the body, displaying thicker glazes on bases.^[19] The traces of kiln supports, as well as the characteristic tendency to run and drip leading to pooling, may indicate the orientation of the object during firing.^[7] In high magnification observations, the interface boundary of body and glaze appears well defined.^[7] The absence of interstitial glass in the core is characteristic of application glazing: however, the possibility of adding glazing mixture to the quartz sand body, as well as the use of pre-melted glazes in the later periods, can predictably increase the degree of sintering of the core ^[14][19]

Recognition of cementation- Objects glazed through cementation display a thin even glaze all over the body, with no drying or firing marks, and portray a fairly friable and soft body^[19][15] Microscopically, the concentration of copper characteristically decreases from the surface: the interaction layer is thin and well defined and the interstitial glass is absent with exception to the vicinity of the boundary layer. ^[7][19]

Recognition of efflorescence glazing- Pieces glazed by efflorescence may show traces of stand marks: the glaze appears thick and prone to cracking, thinning toward the edge of the piece and in concave areas.^[19] In high magnification the interstitial glass is extensive; the unreacted salts which have not reached the surface fuse of the body accumulate in the core, creating bridges between the quartz particles.^[19]

[edit] Typologies

An extensive literature has accumulated in attempt to explain the processing of Egyptian faience and develop an adequate typology that encompasses both technological choices and chemical variations of faience bodies .^{[3][10][19][20]} Body color, density and luster provided the basis of the first typology developed for faience: seven variants were proposed and still permit to distinguish faience objects during field sorting ^[10]

Classification of Body Variants

Most of the categories introduced by Lucas fail to recognize the glazing technology utilized or suggest the stylistic and technological choices embedded in the manufacture of a faience object. However, variant A describes a technologically unique product and as such is still applicable: it has a finely ground underglaze consisting of quartz particles in a glass matrix, often revealed by incisions or depressions cut into the overlying glaze.^[5][14] Glassy faience, variant E, displays no distinct outer layer from the interior, thus it has been suggested that the term 'faience' is a misnomer and the alternative name 'imperfect glass' has been advised.^[5] Regarding variant F specimens, Lucas suggests the use of lead glazes, however it appears that lead was never practiced in Ancient Egypt.^[5][19]

[edit] Workshop evidence

The excavations led by Petrie at Tell-Amarna and Naucratis have reported finding workshop evidence.^[6] Lucas documented a large numbers of molds at the palace area of Amenhotep III, at Qantir from Dynasties 19-20 and at the palace area of Naucratis also described in different sources as a scarab maker's and faience factory.^[10][6] However, seeing as there is a lack of carefully documented archaeological evidence as to the nature of faience factory sites, direct information about the glazing process does not exist. Although recent excavations at the archaeological sites of Abydos and Amarna have supplemented our knowledge of the ancient production of faience gained from the earlier excavated sites of Lisht, Memphis and Naukratis, the differentiation of glass furnaces from faience kilns still remains problematic.^[3] Replication experiments, using modern kilns and replica faience pastes, indicate that faience is fired in the range of 800-1000° ^[21][22]

[edit] Notes

[edit] References

• Binns. 1932. An experiment in Egyptian blue glaze. Journal of the American Ceramic Society.

• Boyce, A. 1989. Notes on the manufacture and use of faience rings at Amarna. In: Kemp, B.J. Amarna Reports V. London: Egypt Exploration Society. 160-168.
• Brill, R.H. 1999. Chemical Analyses of Early Glasses: Volume 1 (tables) and Volume 2 (catalogue), Corning, NY: Corning Museum of Glass,
• Dayton, J.E. Minerals, Metals, Glazing and Man. Edinburgh: Harrap Publishers. 1978.
• Friedman, F.D. (ed.). 1998. Gifts of the Nile-ancient Egyptian faience. London: Thames and Hudson.

• Lucas, A. and Harris, J. R., 1962, Ancient Egyptian materials and industries. London: Edward Arnold.

• Kaczmarczyk, A. and Hedges. R.E.M. 1983. Ancient Egyptian Faience. Warminster: Aris and Phillips.

• Kiefer, C. and Allibert, A. 2007. Pharanoic Blue Ceramics: the Process of Self-glazing. Archaeology 24, 107-117.

• Kiefer, C. 1968. Les céramiques blues, pharanoiques et leur procédé révolutionnaire d'emaillage. Industrie Céramique. May 395-402.

• Kühne, K. 1974 “Frühgeschichtliche Werkstoffe auf Silikatischer Basis”, Das Altertum 20, 67-80
• Nicholson, P.T.1993. Egyptian faience and glass. Aylesbury: Shire- Egyptology.

• Nicholson, P.T. and Peltenburg, E. 2000. Egyptian faience. In: Nicholson, P.T. and Shaw, I. Ancient Egyptian Materials and Technology. Cambridge: Cambridge University Press, 177-194.

• Noble, J. V. 1969. The technique of Egyptian faience. American Journal of Archaeology 73, 435-439.
• Shortland, A.J. and Tite M.S. 2005. A technological study of Ptolemaic – early roman faience from Memphis, Egypt Archaeometry 47/1, 31–46.

• Stone, J. F. S. and Thomas, L. C. 1956. The Use and Distribution of Faience in the Ancient East and Prehistoric Europe, Proceedings of the Prehistoric Society, London 22, 37–84.
• Stocks, D.A.1997. Derivation of ancient Egyptian faience core and glaze materials. Antiquity 71/271, 179-182.

• Petrie, W. M. F.1909. Memphis I, London: British School of Archeology in Egypt.

• Tite, M.S. and Bimson, M. 1986. Faience: an investigation of the microstructures associated with the different methods of glazing, Archaeometry 28, 69–78.

• Tite, M.S., Freestone I.C. and Bimson. M. 1983. Egyptian faience: an investigation of the methods of production, Archaeometry 25, 17–27.
• Vandiver P.B. 1983. Egyptian faience technology, Appendix A. In: A. Kaczmarczyk and R.E.M. Hedges, Editors, Ancient Egyptian Faience,Warminster: Aris and Phillips, A1–A144.
• Vandiver, P. and Kingery, W.D. 1987. Egyptian Faience: the first high-tech ceramic. In Kingery, W.D. ed., Ceramics and Civilisation 3, Columbus OH: American Ceramic Society, 19-34.
• Verges, F.B. 1992. Bleus Egyptiennes. Paris: Louvain
• Wulff, H. E., Wulff, H. S. and Koch, L., 1968. Egyptian faience - a possible survival in Iran. Archeology 21, 98-107.
• Williamson, R.S.1942. The Saqqara Graph. Nature 150, 607-607.