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Ceramic glaze

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Composite body, painted, and glazed bottle. Iran, 16th century (Metropolitan Museum of Art)
Composite body, painted, and glazed bottle. Iran, 16th century (Metropolitan Museum of Art)
Detail of dripping rice-straw ash glaze (top), Japan, 1852
Detail of dripping rice-straw ash glaze (top), Japan, 1852

Ceramic glaze, or simply glaze, is a glassy coating on ceramics. It is used for decoration, to ensure the item is impermeable to liquids and to minimise the adherence of pollutants.[1]

Glazing renders earthenware impermeable to water, sealing the inherent porosity of biscuit earthenware. It also gives a tougher surface. Glaze is also used on stoneware and porcelain. In addition to their functionality, glazes can form a variety of surface finishes, including degrees of glossy or matte finish and color. Glazes may also enhance the underlying design or texture either unmodified or inscribed, carved or painted.

Most pottery produced in recent centuries has been glazed, other than pieces in bisque porcelain, terracotta, or some other types. Tiles are often glazed on the surface face, and modern architectural terracotta is often glazed. Glazed brick is also common. Sanitaryware is invariably glazed, as are many ceramics used in industry, for example ceramic insulators for overhead power lines.

The most important groups of traditional glazes, each named after its main ceramic fluxing agent, are:

Glaze may be applied by spraying, dipping, trailing or brushing on an aqueous suspension of the unfired glaze. The colour of a glaze after it has been fired may be significantly different from before firing. To prevent glazed wares sticking to kiln furniture during firing, either a small part of the object being fired (for example, the foot) is left unglazed or, alternatively, special refractory "spurs" are used as supports. These are removed and discarded after the firing.

Modern materials technology has invented new glazes that do not necessarily conform to these traditional categories.

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Glass

Glass

Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of the molten form; some glasses such as volcanic glass are naturally occurring. The most familiar, and historically the oldest, types of manufactured glass are "silicate glasses" based on the chemical compound silica, the primary constituent of sand. Soda–lime glass, containing around 70% silica, accounts for around 90% of manufactured glass. The term glass, in popular usage, is often used to refer only to this type of material, although silica-free glasses often have desirable properties for applications in modern communications technology. Some objects, such as drinking glasses and eyeglasses, are so commonly made of silicate-based glass that they are simply called by the name of the material.

Earthenware

Earthenware

Earthenware is glazed or unglazed nonvitreous pottery that has normally been fired below 1,200 °C (2,190 °F). Basic earthenware, often called terracotta, absorbs liquids such as water. However, earthenware can be made impervious to liquids by coating it with a ceramic glaze, and is used for the great majority of modern domestic earthenware. The main other important types of pottery are porcelain, bone china, and stoneware, all fired at high enough temperatures to vitrify. End applications include tableware, decorative ware such as figurines.

Porosity

Porosity

Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure the "accessible void", the total amount of void space accessible from the surface.

Biscuit (pottery)

Biscuit (pottery)

Biscuit refers to any pottery that has been fired in a kiln without a ceramic glaze. This can be a final product such as biscuit porcelain or unglazed earthenware or, most commonly, an intermediate stage in a glazed final product.

Porcelain

Porcelain

Porcelain is a ceramic material made by heating raw materials, generally including kaolinite, in a kiln to temperatures between 1,200 and 1,400 °C. The greater strength and translucence of porcelain, relative to other types of pottery, arises mainly from vitrification and formation of the mineral mullite within the body at these high temperatures. End applications include tableware, decorative ware such as figurines, and in technology and industry such as electrical insulators and laboratory ware.

Pottery

Pottery

Pottery is the process and the products of forming vessels and other objects with clay and other raw materials, which are fired at high temperatures to give them a hard and durable form. The place where such wares are made by a potter is also called a pottery. The definition of pottery, used by the ASTM International, is "all fired ceramic wares that contain clay when formed, except technical, structural, and refractory products". End applications include tableware, decorative ware, sanitaryware, and in technology and industry such as electrical insulators and laboratory ware. In art history and archaeology, especially of ancient and prehistoric periods, pottery often means vessels only, and sculpted figurines of the same material are called terracottas.

Biscuit porcelain

Biscuit porcelain

Biscuit porcelain, bisque porcelain or bisque is unglazed, white porcelain treated as a final product, with a matte appearance and texture to the touch. It has been widely used in European pottery, mainly for sculptural and decorative objects that are not tableware and so do not need a glaze for protection.

Architectural terracotta

Architectural terracotta

Architectural terracotta refers to a fired mixture of clay and water that can be used in a non-structural, semi-structural, or structural capacity on the exterior or interior of a building. Terracotta pottery, as earthenware is called when not used for vessels, is an ancient building material that translates from Latin as "baked earth". Some architectural terracotta is actually the stronger stoneware. It can be unglazed, painted, slip glazed, or glazed. A piece of terracotta is composed of a hollow clay web enclosing a void space or cell. The cell can be installed in compression with mortar or hung with metal anchors. All cells are partially backfilled with mortar.

Glazed architectural terra-cotta

Glazed architectural terra-cotta

Glazed architectural terra cotta is a ceramic masonry building material used as a decorative skin. It featured widely in the 'terracotta revival' from the 1880s until the 1930s. It was used in the UK, United States, Canada and Australia and is still one of the most common building materials found in U.S. urban environments. It is the glazed version of architectural terracotta; the material in both its glazed and unglazed versions is sturdy and relatively inexpensive, and can be molded into richly ornamented detail. Glazed terra-cotta played a significant role in architectural styles such as the Chicago School and Beaux-Arts architecture.

Overhead power line

Overhead power line

An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across large distances. It consists of one or more uninsulated electrical cables suspended by towers or poles.

Ceramic flux

Ceramic flux

Fluxes are substances, usually oxides, used in glasses, glazes and ceramic bodies to lower the high melting point of the main glass forming constituents, usually silica and alumina. A ceramic flux functions by promoting partial or complete liquefaction. The most commonly used fluxing oxides in a ceramic glaze contain lead, sodium, potassium, lithium, calcium, magnesium, barium, zinc, strontium, and manganese. These are introduced to the raw glaze as compounds, for example lead as lead oxide. Boron is considered by many to be a glass former rather than a flux.

Kiln furniture

Kiln furniture

Kiln furniture are devices and implements inside furnaces used during the heating of manufactured individual pieces, such as pottery or other ceramic or metal components. Kiln furniture is made of refractory materials, i.e., materials that withstand high temperatures without deformation. Kiln furniture can account for up to 80% of the mass of a kiln charge.

History

Historically, glazing of ceramics developed rather slowly, as appropriate materials needed to be discovered, and also firing technology able to reliably reach the necessary temperatures was needed. Glazes first appeared on stone materials in the 4th millennium BC, and Ancient Egyptian faience (fritware rather than a clay-based material) was self-glazing, as the material naturally formed a glaze-like layer during firing. Glazing of pottery followed the invention of glass around 1500 BC, in the Middle East and Egypt with alkali glazes including ash glaze, and in China, using ground feldspar. By around 100 BC lead-glazing was widespread in the Old World.[3]

Glazed brick goes back to the Elamite Temple at Chogha Zanbil, dated to the 13th century BC. The Iron Pagoda, built in 1049 in Kaifeng, China, of glazed bricks is a well-known later example.[4]

Lead glazed earthenware was probably made in China during the Warring States Period (475 – 221 BCE), and its production increased during the Han Dynasty. High temperature proto-celadon glazed stoneware was made earlier than glazed earthenware, since the Shang Dynasty (1600 – 1046 BCE).[5]

During the Kofun period of Japan, Sue ware was decorated with greenish natural ash glazes. From 552 to 794 AD, differently colored glazes were introduced. The three colored glazes of the Tang Dynasty were frequently used for a period, but were gradually phased out; the precise colors and compositions of the glazes have not been recovered. Natural ash glaze, however, was commonly used throughout the country.

In the 13th century, flower designs were painted with red, blue, green, yellow and black overglazes. Overglazes became very popular because of the particular look they gave ceramics.

From the eighth century, the use of glazed ceramics was prevalent in Islamic art and Islamic pottery, usually in the form of elaborate pottery. Tin-opacified glazing was one of the earliest new technologies developed by the Islamic potters. The first Islamic opaque glazes can be found as blue-painted ware in Basra, dating to around the 8th century. Another significant contribution was the development of stoneware, originating from 9th century Iraq.[6] Other places for innovative pottery in the Islamic world included Fustat (from 975 to 1075), Damascus (from 1100 to around 1600) and Tabriz (from 1470 to 1550).

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Fritware

Fritware

Fritware, also known as stone-paste, is a type of pottery in which frit is added to clay to reduce its fusion temperature. The mixture may include quartz or other siliceous material. An organic compound such as gum or glue may be added for binding. The resulting mixture can be fired at a lower temperature than clay alone. A glaze is then applied on the surface.

Ash glaze

Ash glaze

Ash glazes are ceramic glazes made from the ash of various kinds of wood or straw. They have historically been important in East Asia, especially Chinese pottery, Korean pottery, and Japanese pottery. Many traditionalist East Asian potteries still use ash glazing, and it has seen a large revival in studio pottery in the West and East. Some potters like to achieve random effects by setting up the kiln so that ash created during firing falls onto the pots; this is called "natural" or "naturally occurring" ash glaze. Otherwise the ash is mixed with water, and often clay, and applied as a paste.

Feldspar

Feldspar

Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust, and 41% of the Earth's continental crust by weight.

Elam

Elam

Elam was an ancient civilization centered in the far west and southwest of modern-day Iran, stretching from the lowlands of what is now Khuzestan and Ilam Province as well as a small part of southern Iraq. The modern name Elam stems from the Sumerian transliteration elam(a), along with the later Akkadian elamtu, and the Elamite haltamti. Elamite states were among the leading political forces of the Ancient Near East. In classical literature, Elam was also known as Susiana, a name derived from its capital Susa.

Chogha Zanbil

Chogha Zanbil

Chogha Zanbil is an ancient Elamite complex in the Khuzestan province of Iran. It is one of the few existing ziggurats outside Mesopotamia. It lies approximately 30 km (19 mi) southeast of Susa and 80 km (50 mi) north of Ahvaz.

Iron Pagoda

Iron Pagoda

The Iron Pagoda of Youguo Temple (佑國寺), Kaifeng City, Henan province, is a Buddhist Chinese pagoda built in 1049 during the Song dynasty (960–1279) of China. The pagoda is so-named not because it is made of iron, but because its color resembles that of iron. It is a brick pagoda tower built on the location of a previous wooden one that had been burnt down by lightning fire in 1044. Along with the Liuhe, Lingxiao, Liaodi, Pizhi, and Beisi pagodas, it is seen as a masterpiece of Song dynasty architecture.

Kaifeng

Kaifeng

Kaifeng is a prefecture-level city in east-central Henan province, China. It is one of the Eight Ancient Capitals of China, having been the capital eight times in history, and is best known for having been the Chinese capital during the Northern Song dynasty.

China

China

China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and borders fourteen countries by land, the most of any country in the world, tied with Russia. With an area of approximately 9.6 million square kilometres (3,700,000 sq mi), it is the world's third largest country by total land area. The country consists of 22 provinces, five autonomous regions, four municipalities, and two special administrative regions. The national capital is Beijing, and the most populous city and largest financial center is Shanghai.

Ceramic art

Ceramic art

Ceramic art is art made from ceramic materials, including clay. It may take forms including artistic pottery, including tableware, tiles, figurines and other sculpture. As one of the plastic arts, ceramic art is one of the visual arts. While some ceramics are considered fine art, such as pottery or sculpture, most are considered to be decorative, industrial or applied art objects. Ceramics may also be considered artefacts in archaeology. Ceramic art can be made by one person or by a group of people. In a pottery or ceramic factory, a group of people design, manufacture and decorate the art ware. Products from a pottery are sometimes referred to as "art pottery". In a one-person pottery studio, ceramists or potters produce studio pottery.

Islamic art

Islamic art

Islamic art is a part of Islamic culture and encompasses the visual arts produced since the 7th century CE by people who lived within territories inhabited or ruled by Muslim populations. Referring to characteristic traditions across a wide range of lands, periods, and genres, Islamic art is a concept used first by Western art historians since the late 19th century. Public Islamic art is traditionally non-representational, except for the widespread use of plant forms, usually in varieties of the spiralling arabesque. These are often combined with Islamic calligraphy, geometric patterns in styles that are typically found in a wide variety of media, from small objects in ceramic or metalwork to large decorative schemes in tiling on the outside and inside of large buildings, including mosques. Other forms of Islamic art include Islamic miniature painting, artefacts like Islamic glass or pottery, and textile arts, such as carpets and embroidery.

Islamic pottery

Islamic pottery

Medieval Islamic pottery occupied a geographical position between Chinese ceramics, the unchallenged leaders of Eurasian production, and the pottery of the Byzantine Empire and Europe. For most of the period it can fairly be said to have been between the two in terms of aesthetic achievement and influence as well, borrowing from China and exporting to and influencing Byzantium and Europe. The use of drinking and eating vessels in gold and silver, the ideal in ancient Rome and Persia as well as medieval Christian societies, is prohibited by the Hadiths, with the result that pottery and glass were used for tableware by Muslim elites, as pottery also was in China but was much rarer in Europe and Byzantium. In the same way, Islamic restrictions greatly discouraged figurative wall-painting, encouraging the architectural use of schemes of decorative and often geometrically patterned titles, which are the most distinctive and original specialty of Islamic ceramics.

Basra

Basra

Basra is a city in southern Iraq located on the Shatt al-Arab in the Arabian Peninsula. It had an estimated population of 1.4 million in 2018. Basra is also Iraq's main port, although it does not have deep water access, which is handled at the port of Umm Qasr. However, there is ongoing construction of Grand Faw Port on the coast of Basra, which is considered a national project for Iraq and will become one of the largest ports in the world and the largest in the Middle East, in addition, the port will strengthen Iraq’s geopolitical position in the region and the world. Furthermore, Iraq is planning to establish large naval base in the Faw peninsula.

Composition

Glazes need to include a ceramic flux which functions by promoting partial liquefaction in the clay bodies and the other glaze materials. Fluxes lower the high melting point of the glass forms silica, and sometimes boron trioxide. These glass forms may be included in the glaze materials, or may be drawn from the clay beneath.

Raw materials for ceramic glazes generally include silica, which will be the main glass former. Various metal oxides, such as those of sodium, potassium and calcium, act as flux and therefore lower the melting temperature. Alumina, often derived from clay, stiffens the molten glaze to prevent it from running off the piece.[7] Colorants, such as iron oxide, copper carbonate or cobalt carbonate,[7] and sometimes opacifiers including tin oxide and zirconium oxide, are used to modify the visual appearance of the fired glaze.

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Ceramic flux

Ceramic flux

Fluxes are substances, usually oxides, used in glasses, glazes and ceramic bodies to lower the high melting point of the main glass forming constituents, usually silica and alumina. A ceramic flux functions by promoting partial or complete liquefaction. The most commonly used fluxing oxides in a ceramic glaze contain lead, sodium, potassium, lithium, calcium, magnesium, barium, zinc, strontium, and manganese. These are introduced to the raw glaze as compounds, for example lead as lead oxide. Boron is considered by many to be a glass former rather than a flux.

Boron trioxide

Boron trioxide

Boron trioxide or diboron trioxide is the oxide of boron with the formula B2O3. It is a colorless transparent solid, almost always glassy (amorphous), which can be crystallized only with great difficulty. It is also called boric oxide or boria. It has many important industrial applications, chiefly in ceramics as a flux for glazes and enamels and in the production of glasses.

Sodium

Sodium

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable isotope is 23Na. The free metal does not occur in nature, and must be prepared from compounds. Sodium is the sixth most abundant element in the Earth's crust and exists in numerous minerals such as feldspars, sodalite, and halite (NaCl). Many salts of sodium are highly water-soluble: sodium ions have been leached by the action of water from the Earth's minerals over eons, and thus sodium and chlorine are the most common dissolved elements by weight in the oceans.

Potassium

Potassium

Potassium is the chemical element with the symbol K and atomic number 19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to form flaky white potassium peroxide in only seconds of exposure. It was first isolated from potash, the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals, all of which have a single valence electron in the outer electron shell, which is easily removed to create an ion with a positive charge. In nature, potassium occurs only in ionic salts. Elemental potassium reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, and burning with a lilac-colored flame. It is found dissolved in seawater, and occurs in many minerals such as orthoclase, a common constituent of granites and other igneous rocks.

Calcium

Calcium

Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust, and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The name derives from Latin calx "lime", which was obtained from heating limestone.

Clay

Clay

Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2Si2O5(OH)4).

Iron oxide

Iron oxide

Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of which is rust.

Basic copper carbonate

Basic copper carbonate

Basic copper carbonate is a chemical compound, more properly called copper(II) carbonate hydroxide. It is an ionic compound consisting of the ions copper(II) Cu2+, carbonate CO2−3, and hydroxide OH−.

Tin oxide

Tin oxide

Tin oxide may refer to:Tin(II) oxide (stannous oxide), a black powder with the formula SnO Tin(IV) oxide (tin dioxide, stannic oxide), a white powder with the formula SnO2

Process

Glaze may be applied by dry-dusting a dry mixture over the surface of the clay body or by inserting salt or soda into the kiln at high temperatures to create an atmosphere rich in sodium vapor that interacts with the aluminium and silica oxides in the body to form and deposit glass, producing what is known as salt glaze pottery. Most commonly, glazes in aqueous suspension of various powdered minerals and metal oxides are applied by dipping pieces directly into the glaze. Other techniques include pouring the glaze over the piece, spraying it onto the piece with an airbrush or similar tool, or applying it directly with a brush or other tool.

To prevent the glazed article from sticking to the kiln during firing, either a small part of the item is left unglazed, or it is supported on small refractory supports such as kiln spurs and stilts that are removed and discarded after the firing. Small marks left by these spurs are sometimes visible on finished ware.

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Istanbul

Istanbul

Istanbul, formerly known as Constantinople, is the largest city in Turkey, serving as the country's economic, cultural and historic hub. The city straddles the Bosporus strait, lying in both Europe and Asia, and has a population of over 15 million residents, comprising 19% of the population of Turkey. Istanbul is the most populous European city, and the world's 15th-largest city.

Salt glaze pottery

Salt glaze pottery

Salt-glaze or salt glaze pottery is pottery, usually stoneware, with a glaze of glossy, translucent and slightly orange-peel-like texture which was formed by throwing common salt into the kiln during the higher temperature part of the firing process. Sodium from the salt reacts with silica in the clay body to form a glassy coating of sodium silicate. The glaze may be colourless or may be coloured various shades of brown, blue, or purple.

Mineral

Mineral

In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.

Oxide

Oxide

An oxide is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– ion with oxygen in the oxidation state of −2. Most of the Earth's crust consists of oxides. Even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a thin skin of Al2O3 that protects the foil from further oxidation.

Airbrush

Airbrush

An airbrush is a small, air-operated tool that atomizes and sprays various media, most often paint but also ink and dye, and foundation. Spray painting developed from the airbrush and is considered to employ a type of airbrush.

Kiln

Kiln

A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Kilns have been used for millennia to turn objects made from clay into pottery, tiles and bricks. Various industries use rotary kilns for pyroprocessing and to transform many other materials.

Stilt (ceramics)

Stilt (ceramics)

Stilts are small supports used when firing glazed ceramics to stop the melting glaze from fusing them to each other or the kiln. Stilts are a form of kiln furniture. Their presence in archaeological sites, where they may be known as pernette, along with other kiln furniture such as saggars and kiln bars can be used to support a case for local production. Some potters avoid the need for stilts by not glazing the bottom of their products. This is known as dry footing.

Colour and decoration

Underglaze decoration is applied before the glaze, usually to unfired pottery ("raw" or "greenware") but sometimes to "biscuit"-fired (an initial firing of some articles before the glazing and re-firing).[8][9][10] A wet glaze—usually transparent—is applied over the decoration. The pigment fuses with the glaze, and appears to be underneath a layer of clear glaze; generally the body material used fires to a whitish colour. The best known type of underglaze decoration is the blue and white porcelain first produced in China, and then copied in other countries. The striking blue color uses cobalt as cobalt oxide or cobalt carbonate.[11] However many of the imitative types, such as Delftware, have brownish earthenware bodies, which are given a white tin-glaze and either inglaze or overglaze decoration. With the English invention of creamware and other white-bodied earthenwares in the 18th century, underglaze decoration became widely used on earthenware as well as porcelain.

Sancai coloured lead-glazes in a Tang dynasty tomb guardian.
Sancai coloured lead-glazes in a Tang dynasty tomb guardian.
Chinese celadon shrine; coloured glaze, with the figure left unglazed.  Ming dynasty, 1300-1400
Chinese celadon shrine; coloured glaze, with the figure left unglazed. Ming dynasty, 1300-1400

Overglaze decoration is applied on top of a fired layer of glaze, and generally uses colours in "enamel", essentially glass, which require a second firing at a relatively low temperature to fuse them with the glaze. Because it is only fired at a relatively low temperature, a wider range of pigments could be used in historic periods. Overglaze colors are low-temperature glazes that give ceramics a more decorative, glassy look. A piece is fired first, this initial firing being called the glost firing, then the overglaze decoration is applied, and it is fired again. Once the piece is fired and comes out of the kiln, its texture is smoother due to the glaze.

Other methods are firstly inglaze, where the paints are applied onto the glaze before firing, and then become incorporated within the glaze layer during firing. This works well with tin-glazed pottery, such as maiolica, but the range of colours was limited to those that could withstand a glost firing, as with underglaze. Coloured glazes, where the pigments are mixed into the liquid glaze before it is applied to the pottery, are mostly used to give a single colour to a whole piece, as in most celadons, but can also be used to create designs in contrasting colours, as in Chinese sancai ("three-colour") wares, or even painted scenes.

Many historical styles, for example Japanese Imari ware, Chinese doucai and wucai, combine the different types of decoration. In such cases the first firing for the body, any underglaze decoration and glaze is typically followed by a second firing after the overglaze enamels have been applied.

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Underglaze

Underglaze

Underglaze is a method of decorating pottery in which painted decoration is applied to the surface before it is covered with a transparent ceramic glaze and fired in a kiln. Because the glaze subsequently covers it, such decoration is completely durable, and it also allows the production of pottery with a surface that has a uniform sheen. Underglaze decoration uses pigments derived from oxides which fuse with the glaze when the piece is fired in a kiln. It is also a cheaper method, as only a single firing is needed, whereas overglaze decoration requires a second firing at a lower temperature.

Cobalt blue

Cobalt blue

Cobalt blue is a blue pigment made by sintering cobalt(II) oxide with aluminum(III) oxide (alumina) at 1200 °C. Chemically, cobalt blue pigment is cobalt(II) oxide-aluminium oxide, or cobalt(II) aluminate, CoAl2O4. Cobalt blue is lighter and less intense than the (iron-cyanide based) pigment Prussian blue. It is extremely stable and historically has been used as a coloring agent in ceramics (especially Chinese porcelain), jewelry, and paint. Transparent glasses are tinted with the silica-based cobalt pigment smalt.

Delftware

Delftware

Delftware or Delft pottery, also known as Delft Blue or as delf, is a general term now used for Dutch tin-glazed earthenware, a form of faience. Most of it is blue and white pottery, and the city of Delft in the Netherlands was the major centre of production, but the term covers wares with other colours, and made elsewhere. It is also used for similar pottery, English delftware.

Earthenware

Earthenware

Earthenware is glazed or unglazed nonvitreous pottery that has normally been fired below 1,200 °C (2,190 °F). Basic earthenware, often called terracotta, absorbs liquids such as water. However, earthenware can be made impervious to liquids by coating it with a ceramic glaze, and is used for the great majority of modern domestic earthenware. The main other important types of pottery are porcelain, bone china, and stoneware, all fired at high enough temperatures to vitrify. End applications include tableware, decorative ware such as figurines.

Creamware

Creamware

Creamware is a cream-coloured refined earthenware with a lead glaze over a pale body, known in France as faïence fine, in the Netherlands as Engels porselein, and in Italy as terraglia inglese. It was created about 1750 by the potters of Staffordshire, England, who refined the materials and techniques of salt-glazed earthenware towards a finer, thinner, whiter body with a brilliant glassy lead glaze, which proved so ideal for domestic ware that it supplanted white salt-glaze wares by about 1780. It was popular until the 1840s.

Sancai

Sancai

Sancai is a versatile type of decoration on Chinese pottery using glazes or slip, predominantly in the three colours of brown, green, and a creamy off-white. It is particularly associated with the Tang Dynasty (618–907) and its tomb figures, appearing around 700. Therefore, it is commonly referred to as Chinese: 唐三彩 Tang Sancai in Chinese. Tang sancai wares were sometimes referred in China and the West as egg-and-spinach by dealers, for their use of green, yellow, and white, especially when combined with a streaked effect.

Tang dynasty tomb figures

Tang dynasty tomb figures

Tang dynasty tomb figures are pottery figures of people and animals made in the Tang dynasty of China (618–906) as grave goods to be placed in tombs. There was a belief that the figures represented would become available for the service of the deceased in the afterlife. The figures are made of moulded earthenware with colour generally being added, though often not over the whole figure, or in naturalistic places. Where the colouring was in paint it has often not survived, but in many cases it was in sancai ("three-colour") ceramic glaze, which has generally lasted well.

Celadon

Celadon

Celadon is a term for pottery denoting both wares glazed in the jade green celadon color, also known as greenware or "green ware", and a type of transparent glaze, often with small cracks, that was first used on greenware, but later used on other porcelains. Celadon originated in China, though the term is purely European, and notable kilns such as the Longquan kiln in Zhejiang province are renowned for their celadon glazes. Celadon production later spread to other parts of East Asia, such as Japan and Korea as well as Southeast Asian countries such as Thailand. Eventually, European potteries produced some pieces, but it was never a major element there. Finer pieces are in porcelain, but both the color and the glaze can be produced in stoneware and earthenware. Most of the earlier Longquan celadon is on the border of stoneware and porcelain, meeting the Chinese but not the European definitions of porcelain.

Overglaze decoration

Overglaze decoration

Overglaze decoration, overglaze enamelling or on-glaze decoration is a method of decorating pottery, most often porcelain, where the coloured decoration is applied on top of the already fired and glazed surface, and then fixed in a second firing at a relatively low temperature, often in a muffle kiln. It is often described as producing "enamelled" decoration. The colours fuse on to the glaze, so the decoration becomes durable. This decorative firing is usually done at a lower temperature which allows for a more varied and vivid palette of colours, using pigments which will not colour correctly at the high temperature necessary to fire the porcelain body. Historically, a relatively narrow range of colours could be achieved with underglaze decoration, where the coloured pattern is applied before glazing, notably the cobalt blue of blue and white porcelain.

Maiolica

Maiolica

Maiolica is tin-glazed pottery decorated in colours on a white background. The most renowned Italian maiolica is from the Renaissance period. These works were known as istoriato wares when depicting historical and mythical scenes. By the late 15th century, multiple locations, mainly in northern and central Italy, were producing sophisticated pieces for a luxury market in Italy and beyond. In France, maiolica developed as faience, in the Netherlands and England as delftware, and in Spain as talavera. In English, the spelling was anglicised to majolica, but the pronunciation usually preserved the vowel with an i as in kite.

Imari ware

Imari ware

Imari ware is a Western term for a brightly-coloured style of Arita ware Japanese export porcelain made in the area of Arita, in the former Hizen Province, northwestern Kyūshū. They were exported to Europe in large quantities, especially between the second half of the 17th century and the first half of the 18th century.

Doucai

Doucai

Doucai is a technique in painting Chinese porcelain, where parts of the design, and some outlines of the rest, are painted in underglaze blue, and the piece is then glazed and fired. The rest of the design is then added in overglaze enamels of different colours and the piece fired again at a lower temperature of about 850°C to 900°C.

Environmental impact

Glazed stupa model, Yuan dynasty
Glazed stupa model, Yuan dynasty

Heavy metals are dense metals used in glazes to produce a particular color or texture.[9] Glaze components are more likely to be leached into the environment when non-recycled ceramic products are exposed to warm or acidic water.[12] Leaching of heavy metals occurs when ceramic products are glazed incorrectly or damaged.[12] Lead and chromium are two heavy metals which can be used in ceramic glazes that are heavily monitored by government agencies due to their toxicity and ability to bioaccumulate.[12][13]

Metal oxide chemistry

Metals used in ceramic glazes are typically in the form of metal oxides.

Lead(II) oxide

Ceramic manufacturers primarily use lead(II) oxide (PbO) as a flux for its low melting range, wide firing range, low surface tension, high index of refraction, and resistance to devitrification.[14] Lead used in the manufacture of commercial glazes are molecularly bound to silica in a 1:1 ratio, or included in frit form, to ensure stabilization and reduce the risk of leaching. [15]

In polluted environments, nitrogen dioxide reacts with water (H
2
O
) to produce nitrous acid (HNO
2
) and nitric acid (HNO
3
).[13]

H
2
O
+ 2NO
2
HNO
2
+ HNO
3

Soluble Lead(II) nitrate (Pb(NO
3
)
2
) forms when lead(II) oxide (PbO) of leaded glazes is exposed to nitric acid (HNO
3
)

PbO + 2HNO
3
Pb(NO
3
)
2
+ H
2
O

Because lead exposure is strongly linked to a variety of health problems, collectively referred to as lead poisoning, the disposal of leaded glass (chiefly in the form of discarded CRT displays) and lead-glazed ceramics is subject to toxic waste regulations.

Barium carbonate and Strontium carbonate

Barium carbonate (BaCO3) is used to create a unique glaze color known as barium blue. However, the ethical nature of using barium carbonate for glazes on food contact surfaces has come into question. Barium poisoning by ingestion can result in convulsions, paralysis, digestive discomfort, and death.[16] It is also somewhat soluble in acid,[17] and can contaminate water and soil for long periods of time. These concerns have led to attempts to substitute Strontium carbonate (SrCO3) in glazes that require barium carbonate.[18] Unlike Barium carbonate, Strontium carbonate is not considered a safety hazard by the NIH.[19][17] Experiments in strontium substitution tend to be successful in gloss type glazes, although there are some effects and colors produced in matte type glazes that can only be obtained through use of barium. [18]

To reduce the likelihood of leaching, barium carbonate is used in frit form and bound to silica in a 1:1 ratio. It is also recommended that barium glazes not be used on food contact surfaces or outdoor items. [20]

Chromium(III) oxide

Chromium(III) oxide (Cr
2
O
3
) is used as a colorant in ceramic glazes. Chromium(III) oxide can undergo a reaction with calcium oxide (CaO) and atmospheric oxygen in temperatures reached by a kiln to produce calcium chromate (CaCrO
4
). The oxidation reaction changes chromium from its +3 oxidation state to its +6 oxidation state.[21] Chromium(VI) is very soluble and the most mobile out of all the other stable forms of chromium.[22]

Cr
2
O
3
+ 2CaO + 32O
2
CaCrO
4
[21]

Chromium may enter water systems via industrial discharge. Chromium(VI) can enter the environment directly or oxidants present in soils can react with chromium(III) to produce chromium(VI). Plants have reduced amounts of chlorophyll when grown in the presence of chromium(VI).[22]

Uranium(IV) oxide (UO2)

Urania-based ceramic glazes are dark green or black when fired in a reduction or when UO2 is used; more commonly it is used in oxidation to produce bright yellow, orange and red glazes[23] Uranium glazes were used in the 1920s and 1930s for making uranium tile, watch, clock and aircraft dials.[24]

Uranium dioxide is produced by reducing uranium trioxide with hydrogen.

UO3 + H2 → UO2 + H2O at 700 °C (973 K)

Prevention

Chromium oxidation during manufacturing processes can be reduced with the introduction of compounds that bind to calcium.[21] Ceramic industries are reluctant to use lead alternatives since leaded glazes provide products with a brilliant shine and smooth surface. The United States Environmental Protection Agency has experimented with a dual glaze, barium alternative to lead, but they were unsuccessful in achieving the same optical effect as leaded glazes.

Discover more about Environmental impact related topics

Lead(II) oxide

Lead(II) oxide

Lead(II) oxide, also called lead monoxide, is the inorganic compound with the molecular formula PbO. PbO occurs in two polymorphs: litharge having a tetragonal crystal structure, and massicot having an orthorhombic crystal structure. Modern applications for PbO are mostly in lead-based industrial glass and industrial ceramics, including computer components. It is an amphoteric oxide.

Devitrification

Devitrification

Devitrification is the process of crystallization in a formerly crystal-free (amorphous) glass. The term is derived from the Latin vitreus, meaning glassy and transparent.

Frit

Frit

A frit is a ceramic composition that has been fused, quenched, 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 by causing them to combine with silica and other added oxides. However, not all glass that is fused and quenched in water is frit, as this method of cooling down very hot glass is also widely used in glass manufacture.

Nitrogen dioxide

Nitrogen dioxide

Nitrogen dioxide is a chemical compound with the formula NO2. It is one of several nitrogen oxides. NO2 is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year for use primarily in the production of fertilizers. At higher temperatures it is a reddish-brown gas. It can be fatal if inhaled in large quantities. Nitrogen dioxide is a paramagnetic, bent molecule with C2v point group symmetry.

Nitric acid

Nitric acid

Nitric acid is the inorganic compound with the formula HNO3. It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitric acid has a concentration of 68% in water. When the solution contains more than 86% HNO3, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as red fuming nitric acid at concentrations above 86%, or white fuming nitric acid at concentrations above 95%.

Lead(II) nitrate

Lead(II) nitrate

Lead(II) nitrate is an inorganic compound with the chemical formula Pb(NO3)2. It commonly occurs as a colourless crystal or white powder and, unlike most other lead(II) salts, is soluble in water.

Lead poisoning

Lead poisoning

Lead poisoning, also known as plumbism and saturnism, is a type of metal poisoning caused by lead in the body. The brain is the most sensitive. Symptoms may include abdominal pain, constipation, headaches, irritability, memory problems, infertility, and tingling in the hands and feet. It causes almost 10% of intellectual disability of otherwise unknown cause and can result in behavioral problems. Some of the effects are permanent. In severe cases, anemia, seizures, coma, or death may occur.

Barium carbonate

Barium carbonate

Barium carbonate is the inorganic compound with the formula BaCO3. Like most alkaline earth metal carbonates, it is a white salt that is poorly soluble in water. It occurs as the mineral known as witherite. In a commercial sense, it is one of the most important barium compounds.

National Institutes of Health

National Institutes of Health

The National Institutes of Health, commonly referred to as NIH, is the primary agency of the United States government responsible for biomedical and public health research. It was founded in the late 1880s and is now part of the United States Department of Health and Human Services. Many NIH facilities are located in Bethesda, Maryland, and other nearby suburbs of the Washington metropolitan area, with other primary facilities in the Research Triangle Park in North Carolina and smaller satellite facilities located around the United States. The NIH conducts its own scientific research through the NIH Intramural Research Program (IRP) and provides major biomedical research funding to non-NIH research facilities through its Extramural Research Program.

Chromium(III) oxide

Chromium(III) oxide

Chromium(III) oxide is an inorganic compound with the formula Cr2O3. It is one of the principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.

Calcium oxide

Calcium oxide

Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "lime" connotes calcium-containing inorganic materials, in which carbonates, oxides and hydroxides of calcium, silicon, magnesium, aluminium, and iron predominate. By contrast, quicklime specifically applies to the single chemical compound calcium oxide. Calcium oxide that survives processing without reacting in building products such as cement is called free lime.

Calcium chromate

Calcium chromate

Calcium chromate is an inorganic compound with the formula CaCrO4, i.e. the chromate salt of calcium. It is a bright yellow solid which is normally found in the dihydrate form CaCrO4·2H2O. A very rare anhydrous mineral form exists in nature, which is known as chromatite.

Gallery

Source: "Ceramic glaze", Wikipedia, Wikimedia Foundation, (2023, March 17th), https://en.wikipedia.org/wiki/Ceramic_glaze.

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See also
References
  1. ^ Division, Company Statistics. "Statistics of U.S. Businesses Main Page". www.census.gov. Archived from the original on 26 November 2015. Retrieved 27 November 2015.
  2. ^ C D Fortnum, 1875, Maiolica, Chapter II on Enamelled or Stanniferous Glazed Wares "It was found that by the addition of a certain portion of the oxide of tin to the composition of glass and oxide of lead the character of the glaze entirely alters. Instead of being translucent it becomes, on fusion, an opaque and beautifully white enamel…"
  3. ^ Paul T. Craddock (2009). Scientific Investigation of Copies, Fakes and Forgeries. Routledge. p. 207. ISBN 978-0-7506-4205-7. Pottery only began to be glazed from the mid second millennium BC, coincident with the first production of glass.
  4. ^ Daiheng, Gao (2002). Chinese Architecture – The Lia, Song, Xi Xia and Jin Dynasties (English ed.). Yale University Press. pp. 166, 183. ISBN 978-0-300-09559-3.
  5. ^ Zhiyan, Li (2002). Chinese Ceramics -- From the Paleolithic Period through the Qing Dynasty (English ed.). New York & London, Beijing: Yale University Press, Foreign Languages Press. pp. 144, 145, 152. ISBN 978-0-300-11278-8.
  6. ^ Mason (1995), p. 5
  7. ^ a b Madan, Gaurav (2005). S.Chands Success Guide (Q&A) Inorganic Chemistry. S. Chand Publishing. ISBN 9788121918572.
  8. ^ "Cleaning Biscuit Fired Ceramic Ware" Hulse D.K, Barnett W.C. UK Pat.Appl.GB2287643A
  9. ^ a b Denio, Allen A. (1 April 1980). "Chemistry for potters". Journal of Chemical Education. 57 (4): 272. Bibcode:1980JChEd..57..272D. doi:10.1021/ed057p272.
  10. ^ "Roller Kilns For The Fast Biscuit And Glost Firing Of Porcelain" Rodriguez Mamolar M.J., De La Fuente Revuelta J. Ceram. Inf.(Spain) 20, No.202. 1994. Pg. 25–27
  11. ^ 'Ceramics Glaze Technology.' J.R.Taylor & A.C.Bull. The Institute Of Ceramics & Pergamon Press. Oxford. 1986
  12. ^ a b c Omolaoye, J.A,, A. Uzairu, and C.E. Gimba. "Heavy Metal Assessment of Some Ceramic Products Imported into Nigeria from China." Archives of Applied Science Research 2.5 (2010): 120-25. Web. 15 October 2015
  13. ^ a b Baltrusaitis, Jonas; Chen, Haihan; Rubasinghege, Gayan; Grassian, Vicki H. (4 December 2012). "Heterogeneous Atmospheric Chemistry of Lead Oxide Particles with Nitrogen Dioxide Increases Lead Solubility: Environmental and Health Implications". Environmental Science & Technology. 46 (23): 12806–12813. Bibcode:2012EnST...4612806B. doi:10.1021/es3019572. ISSN 0013-936X. PMC 3518381. PMID 23057678.
  14. ^ Lehman, Richard. Lead Glazes for Ceramic Foodware. 1st ed. Research Triangle Park: International Lead Management Center, 2002. International Lead Management Center Archived 27 January 2018 at the Wayback Machine
  15. ^ Pan, De'an (20 February 2018). "Characteristics and properties of glass-ceramics using lead fuming slag". Journal of Cleaner Production. 175: 251–256. doi:10.1016/j.jclepro.2017.12.030 – via Elsevier Science Direct.
  16. ^ "ATSDR - Public Health Statement: Barium". www.atsdr.cdc.gov. Retrieved 28 April 2020.
  17. ^ a b PubChem. "Barium carbonate". pubchem.ncbi.nlm.nih.gov. Retrieved 28 April 2020.
  18. ^ a b Semler, Daniel (17 November 2009). "Leaving Bariumville: Replacing Barium Carbonate in Cone 10 Glazes". Ceramic Arts Daily. Retrieved 27 April 2020.
  19. ^ PubChem. "Strontium carbonate". pubchem.ncbi.nlm.nih.gov. Retrieved 7 May 2020.
  20. ^ Hansen, Tony. "Barium in Materials and Fired Glazes (hazard)". digitalfire.com. Retrieved 7 May 2020.
  21. ^ a b c Verbinnen, Bram; Billen, Pieter; Van Coninckxloo, Michiel; Vandecasteele, Carlo (4 June 2013). "Heating Temperature Dependence of Cr(III) Oxidation in the Presence of Alkali and Alkaline Earth Salts and Subsequent Cr(VI) Leaching Behavior". Environmental Science & Technology. 47 (11): 5858–5863. Bibcode:2013EnST...47.5858V. doi:10.1021/es4001455. ISSN 0013-936X. PMID 23635007.
  22. ^ a b Oliveira, Helena (20 May 2012). "Chromium as an Environmental Pollutant: Insights on Induced Plant Toxicity". Journal of Botany. 2012: 1–8. doi:10.1155/2012/375843.
  23. ^ Örtel, Stefan. Uran in der Keramik. Geschichte - Technik - Hersteller
  24. ^ Uranium tile
Bibliography

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