Egyptian faience is a non-clay based ceramic

Ceramic

A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...

 displaying surface vitrification

Glass transition

The liquid-glass transition is the reversible transition in amorphous materials from a hard and relatively brittle state into a molten or rubber-like state. An amorphous solid that exhibits a glass transition is called a glass...

 which creates a bright lustre of various blue-green colours. Having not been made from clay it is often not classed as pottery

Pottery

Pottery is the material from which the potteryware is made, of which major types include earthenware, stoneware and porcelain. The place where such wares are made is also called a pottery . Pottery also refers to the art or craft of the potter or the manufacture of pottery...

. It is called "Egyptian faience" to distinguish it from faience

Faience

Faience or faïence is the conventional name in English for fine tin-glazed pottery on a delicate pale buff earthenware body, originally associated with Faenza in northern Italy. The invention of a white pottery glaze suitable for painted decoration, by the addition of an oxide of tin to the slip...

, the tin glazed pottery

Tin-glazed pottery

Tin-glazed pottery is a majolica pottery covered in glaze containing tin oxide which is white, shiny and opaque. The pottery body is usually made of red or buff colored earthenware and the white glaze was often used to imitate Chinese porcelain...

 associated with Faenza

Faenza

Faenza is an Italian city and comune, in the province of Ravenna, Emilia-Romagna, situated 50 km southeast of Bologna.Faenza is noted for its manufacture of majolica ware glazed earthenware pottery, known from the name of the town as "faience"....

 in northern Italy. Egyptian faience, both locally produced and exported from Egypt, occurred widely in the ancient world, and is well known from Mesopotamia, the Mediterranean and in northern Europe as far away as Scotland.

Introduction

From the inception of faience in the archaeological record of Ancient Egypt

Ancient Egypt

Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

, the elected colors of the glaze

Ceramic glaze

Glaze is a layer or coating of a vitreous substance which has been fired to fuse to a ceramic object to color, decorate, strengthen or waterproof it.-Use:...

s varied within an array of blue-green hues. Glazed in these colours, faience was perceived as substitute for blue-green materials such as turquoise

Turquoise

Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium, with the chemical formula CuAl648·4. It is rare and valuable in finer grades and has been prized as a gem and ornamental stone for thousands of years owing to its unique hue...

, found in the Sinai peninsula, and lapis lazuli

Lapis lazuli

Lapis lazuli is a relatively rare semi-precious stone that has been prized since antiquity for its intense blue color....

, from Afghanistan

Afghanistan

Afghanistan , officially the Islamic Republic of Afghanistan, is a landlocked country located in the centre of Asia, forming South Asia, Central Asia and the Middle East. With a population of about 29 million, it has an area of , making it the 42nd most populous and 41st largest nation in the world...

. As early as the Predynastic graves at Naqada

Naqada

Naqada is a town on the west bank of the Nile in the Egyptian governorate of Qena. It was known in Ancient Egypt as Nubt and in classical antiquity as Ombos. Its name derives from ancient Egyptian nub, meaning gold, on account of the proximity of gold mines in the Eastern Desert.Naqada comprises...

, Badar, el-Amrah, Matmar, Harageh, Avadiyedh and El-Gerzeh, glazed steatite and faience beads are found associated with these semi-precious stones. 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

New Kingdom

The New Kingdom of Egypt, also referred to as the Egyptian Empire is the period in ancient Egyptian history between the 16th century BC and the 11th century BC, covering the Eighteenth, Nineteenth, and Twentieth Dynasties of Egypt....

 had also come to refer to the 'substitute', faience. The symbolism embedded in blue glazing could recall both the Nile

Nile

The Nile is a major north-flowing river in North Africa, generally regarded as the longest river in the world. It is long. It runs through the ten countries of Sudan, South Sudan, Burundi, Rwanda, Democratic Republic of the Congo, Tanzania, Kenya, Ethiopia, Uganda and Egypt.The Nile has two major...

, the waters of heaven

Heaven

Heaven, the Heavens or Seven Heavens, is a common religious cosmological or metaphysical term for the physical or transcendent place from which heavenly beings originate, are enthroned or inhabit...

 and the home of the god

God

God is the English name given to a singular being in theistic and deistic religions who is either the sole deity in monotheism, or a single deity in polytheism....

s, whereas green could possibly evoke images of regeneration, rebirth and vegetation.

Relationship with Egyptian copper industry

The discovery of faience glazing has tentatively been associated with the copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 industry: bronze

Bronze

Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...

 scale and corrosion products of leaded copper objects are found in the manufacture of faience pigment

Pigment

A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...

s. However, although the likelihood of glazed quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 pebbles developing accidentally in traces in copper smelting

Smelting

Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...

 furnace

Furnace

A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...

s from the copper and wood ash is high, the regions in which these processes originate do not coincide.

Relationship with Egyptian glass industry

Although it appears no glass

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

 was intentionally produced in Egypt prior to the 18th dynasty, it is likely that faience, frit

Frit

Frit is a ceramic composition that has been fused in a special fusing oven, quenched to form a glass, and granulated. Frits form an important part of the batches used in compounding enamels and ceramic glazes; the purpose of this pre-fusion is to render any soluble and/or toxic components insoluble...

 and glass were all made in close proximity or in the same workshop complex, seeing as developments in one industry are reflected in others. Such close relationship is reflected in the prominent similarity of the formulations of faience glaze and contemporary glass compositions. Despite the differences in the pyrotechnology of glass and faience, the latter being worked cold, archaeological evidence suggests that New Kingdom

New Kingdom

The New Kingdom of Egypt, also referred to as the Egyptian Empire is the period in ancient Egyptian history between the 16th century BC and the 11th century BC, covering the Eighteenth, Nineteenth, and Twentieth Dynasties of Egypt....

 glass and faience production was undertaken in the same workshops.

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. Egyptian faience is a non-clay based ceramic composed of crushed quartz or sand, with small amounts of calcite

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

 lime and a mixture of alkali

Alkali

In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...

s, displaying surface vitrification

Glass transition

The liquid-glass transition is the reversible transition in amorphous materials from a hard and relatively brittle state into a molten or rubber-like state. An amorphous solid that exhibits a glass transition is called a glass...

 due to the soda lime

Soda-lime glass

Soda-lime glass, also called soda-lime-silica glass, is the most prevalent type of glass, used for windowpanes, and glass containers for beverages, food, and some commodity items...

 silica glaze

Ceramic glaze

Glaze is a layer or coating of a vitreous substance which has been fired to fuse to a ceramic object to color, decorate, strengthen or waterproof it.-Use:...

 often composed of copper pigments to create a bright blue-green luster. 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. Plant ash, from halophitic plants typical of dry and sea areas, was the major source of alkali until the Ptolemaic Period, when natron

Natron

Natron is a naturally occurring mixture of sodium carbonate decahydrate and about 17% sodium bicarbonate along with small quantities of household salt and sodium sulfate. Natron is white to colourless when pure, varying to gray or yellow with impurities...

 based alkalis almost completely replaced the previous source. 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.

Faience working technology

Typical faience mixture is thixotropic, that is thick at first and then soft and flowing as it begins to be formed.
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. If pressed too vigorously this material will resist flow until it yields and cracks, due to its limited plastic deformation and low yield strength.

Body binding technology

A number of possible binding agents, amongst Arabic gum, clay

Clay

Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

, lime, egg white

Egg white

Egg white is the common name for the clear liquid contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms around either fertilized or unfertilized egg yolks...

 and resin

Resin

Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...

, have been suggested to help in the binding process. 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. The use of alkalis as binders, in the form of natron or plant ash, produced suitable results in experiments. 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.

Body working technology

Three methods have been hypothesized to shape the body of faience objects: modeling, moulding and abrasion, the last being used in conjunction with the first two. 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. 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.
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. Marbleized faience, resulting from the working of different colored faience bodies together, so as to produce a uniform adherent body, also appears in this period. Towards the end of the Middle Kingdom, incising, inlaying and resisting techniques appear: these were bound to become progressively popular towards the New Kingdom. In the New Kingdom, beads, amulets and finger rings are produced by a combination of modeling and molding techniques. In this period, sculptural detail is created using inlays of different colored faience or by scraping the body to reveal the white intermediate layer in relief. 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. The faience paste could then be pressed into the mold, and following drying, be re-worked through surface abrasion before firing. 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.

Wheel throwing, possibly occurring from the New Kingdom onwards, is certainly established by the Greco-Roman period, when large amounts of clay seem to have been added to the faience body. 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.

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.

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. 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. 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.

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. 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.

Cementation glazing

Cementation glazing, a technique discovered in the Middle Kingdom, is also a self-glazing technique. 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

Qom

Qom is a city in Iran. It lies by road southwest of Tehran and is the capital of Qom Province. At the 2006 census, its population was 957,496, in 241,827 families. It is situated on the banks of the Qom River....

' in Iran in 1960s. In this method the artifact, 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.

Alternative techniques

A vapour glaze reaction similar to salt glazing, as 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.

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. 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. The following proposed criteria are subject to variation caused by increases in flux concentration, firing temperatures and time at peak temperatures.

Recognition of application glazing- Macroscopically, applied glazes vary in thickness through the body, displaying thicker glazes on bases. 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. In high magnification observations, the interface boundary of body and glaze appears well defined. 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

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 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.

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. 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.

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. 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.

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. 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. Regarding variant F specimens, Lucas suggests the use of lead glazes, however it appears that lead glazing was never practiced in Ancient Egypt.

Workshop evidence

The excavations led by Petrie at Tell-Amarna and Naucratis have reported finding workshop evidence. Lucas documented a large number 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. However, seeing 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. Replication experiments, using modern kilns and replica faience pastes, indicate that faience is fired in the range of 800-1000°