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A History of Pottery

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					A History of Pottery
The production of pottery is one of the most ancient arts. The oldest known body of
pottery dates from the Jomon period (from about 10,500 to 400 BC) in Japan; and even
the earliest Jomon ceramics exhibit a unique sophistication of technique and design.
Excavations in the Near East have revealed that primitive fired-clay vessels were made
there more than 8,000 years ago. Potters were working in Iran by about 5500 BC, and
earthenware was probably being produced even earlier on the Iranian high plateau.
Chinese potters had developed characteristic techniques by about 5000 BC. In the New
World many pre-Columbian American cultures developed highly artistic pottery
traditions.

After general sections on basic pottery types and decorating techniques this article
focuses on the development of Western pottery since the beginning of the Renaissance.
For detailed treatment of ancient Western and non-Western pottery, see Chinese art and
architecture; Egypt, ancient; Greek art; Islamic art and architecture; Japanese art and
architecture; Korean art; Mesopotamia; Minoan art; Persian art and architecture; pre-
Columbian art and architecture.

TYPES OF WARES

Pottery comprises three distinctive types of wares. The first type, earthenware, has been
made following virtually the same techniques since ancient times; only in the modern
era has mass production brought changes in materials and methods. Earthenware is
basically composed of clay--often blended clays--and baked hard, the degree of
hardness depending on the intensity of the heat. After the invention of glazing,
earthenwares were coated with glaze to render them waterproof; sometimes glaze was
applied decoratively. It was found that, when fired at great heat, the clay body became
nonporous. This second type of pottery, called stoneware, came to be preferred for
domestic use.

The third type of pottery is a Chinese invention that appeared when feldspathic material
in a fusible state was incorporated in a stoneware composition. The ancient Chinese
called decayed feldspar kaolin (meaning "high place," where it was originally found);
this substance is known in the West as china clay. Petuntse, or china stone, a less
decayed, more fusible feldspathic material, was also used in Chinese porcelain; it forms
a white cement that binds together the particles of less fusible kaolin. Significantly, the
Chinese have never felt that high-quality porcelain must be either translucent or white.
Two types of porcelain evolved: "true" porcelain, consisting of a kaolin hard-paste
body, extremely glassy and smooth, produced by high temperature firing, and soft
porcelain, invariably translucent and lead glazed, produced from a composition of
ground glass and other ingredients including white clay and fired at a low temperature.
The latter was widely produced by 18th-century European potters.

It is believed that porcelain was first made by Chinese potters toward the end of the Han
period (206 BC-AD 220), when pottery generally became more refined in body, form,
and decoration. The Chinese made early vitreous wares (protoporcelain) before they
developed their white vitreous ware (true porcelain) that was later so much admired by
Europeans.
Regardless of time or place, basic pottery techniques have varied little except in ancient
America, where the potter's wheel was unknown. Among the requisites of success are
correct composition of the clay body by using balanced materials; skill in shaping the
wet clay on the wheel or pressing it into molds; and, most important, firing at the
correct temperature. The last operation depends vitally on the experience, judgment, and
technical skill of the potter.

DECORATING TECHNIQUES

In the course of their long history potters have used many decorating techniques.
Among the earliest, impressing and incising of wares are still favored. Ancient potters
in Egypt, Mesopotamia, Greece, northern India and the high regions of Central Asia
(where primitive terra-cotta figures, associated with religious cults were produced)
frequently decorated wares with impressed or incised designs. A notable incising
technique developed more recently was that of Korean potters working in the Koryo
period (918-1392). These artisans began by ornamenting their celadon wares with
delicately incised and impressed patterns and later developed elaborate inlaying by
filling incised lines with colored slip (semiliquid clay). Black and white slip was used
most effectively for inlaying colored porcelains. Decoration of this sort generally
depends more on the skill of the artisan than on the complexity of the tools being used.

An especially popular type of decoration involved the sgraffito, or "scratched,"
technique used by Italian potters before the 15th century. This technique, which is
thought to have reached Italy from the Near East, was probably derived from China,
where it was first used during the Song (Sung) dynasty (960-1279). By the 16th century
Italian potters working mainly in Padua and Bologna had developed great skill in
sgraffito, which entailed the incising of designs on red or buff earthenware that had
been coated with ordinary transparent lead glaze, usually toned yellow or, sometimes,
brown, copper, or green. After firing, the wares were dipped into white clay slip so that
a dark pattern could be cut on the surface. By cutting through the white slip, the artist
produced a design on the exposed red or buff body. Pigments were also sometimes
applied. After a further coating of lead glaze the ware was fired a second time.

A sound knowledge of glazes--both utilitarian and decorative--is vital to the potter. The
origin of glazes and glazing techniques is unknown, but the fine lustrous glazes
developed in China surely began with a simple glaze that served to cover earthenware
and render it watertight. Chinese potters used two kinds of glazes, one composed
basically of feldspar, and another produced by fusing silica of quartz or sand by means
of a flux, generally of lead oxide.

Chinese potters regarded glazes and glazing techniques as having prime importance;
under the Han emperors they made great efforts to improve this technology. The use of
lead glaze increased, and wood ash was incorporated to impart a dullish brown or gray
green coloring, somewhat blotchy and occasionally iridescent. These effects were
entirely natural, as no coloring matter was added to the composition. Glazing techniques
were modified under successive dynasties. Colored glazes were developed and used to
brilliant effect by Tang (T'ang) and Song potters, and a great diversity of brightly hued
wares appeared over the centuries.
Many connoisseurs feel that the pure white porcelain, called blanc de chine, which first
appeared during the Ming dynasty, is the most serenely beautiful of all Chinese
ceramics. Dehua (Te-hua) potters in Fujian (Fukien) province, working during the 17th
century, produced their blanc de chine masterpieces in the purest white porcelain coated
with a thick white glaze.

Salt glaze, used by English potters during the early 1700s, may well have been known
to the Chinese but was not used by them. Near Eastern potters glazed wares in ancient
times. Potters in Mesopotamia and Iran commonly used an alkaline glaze made of
quartz mixed with sodium and potassium. An admixture of colored metallic oxides,
mostly lead, was introduced later.

Painting on pottery and porcelain became richly colorful in many regions and periods.
Decorative brush painting directly on the baked clay reached its zenith in China during
the Ming dynasty (1368-1644), whose artists were highly skilled at painting in fired
colors. For a long period Chinese ceramic artists had used only black or brown pigment
to decorate wares that were then covered with clear glaze. It is believed that the
appearance in China of 13th-century brush-decorated wares from Persia sparked a
change. These works, painted in blue cobalt under the glaze, inspired the brushwork of
the Chinese and the resulting so-called blue-and-white style.

Ming artists also excelled in painting over the glaze, using brilliant enamel colors. The
overglaze technique, which evolved over two centuries, demanded correct preparation
of the enamels, skill in application, and the proper (low) firing temperature. The
overglaze enamel decorations executed during the reign of Chenghua (1465-87), which
were never surpassed in China, incorporated flowers, foliage, and figure subjects against
backgrounds of arabesques and scrollwork. Designs enclosed within dark blue outlines
were filled in with brilliant color. Enamel decoration of superb quality was also
executed in Japan during the Edo period (1615-1868) by celebrated artists and potters of
the caliber of Kenzan, Kakiemon, and Ninsei.

In the ancient Aegean the potter's art developed continuously from the Neolithic period
and through the periods of the Minoan and Mycenaean civilizations, culminating, in
ancient Greece, in a unique type of painted pottery, which reached its height between
the 6th and 4th centuries BC. The finest Greek pottery, especially Attic vases, was
exquisitely proportioned and often decorated with finely painted relief work. Unlike
artisans in Egypt, Mesopotamia, and Persia, the Attic potters did not apply heavy glaze
to their wares. The unique gloss commonly seen on Attic pottery and similar wares
made elsewhere in Greece still baffles those who have tried to determine its formula and
method of application. Neither a glaze nor a varnish, it is more marked on some areas,
such as those painted black, than on others. Some experts conjecture that it may be
attributed to illite or a similar clay mineral in a weak solution that was thinly applied to
the surface of wares or mixed into the black "paint" used by the artists.

In the Islamic world ceramic decorative art flowered with the creation of a great
diversity of painted wares. Painted luster decoration on pottery originated in
Mesopotamia and spread to ancient Egypt; later, under Islam in Persia, this type of
decoration on white-glazed wares became incredibly brilliant. Islamic luster-painted
wares were later imitated by Italian potters during the Renaissance.
MAJOR TRADITIONS IN THE WEST

After the fall of the ancient Roman Empire potters in Europe produced little other than
repetitive utilitarian wares until the end of the Middle Ages.



Earthenware

A distinctive type of earthenware known as majolica, which was derived from Chinese
porcelain, appeared in Italy during the last quarter of the 14th century. It is now
believed that this type of painted earthenware was inspired by the Hispano-Moresque
luster-decorated ware of Spanish origin introduced to Italy by Majorcan seagoing
traders.

Majolica ware, whether thrown on the wheel or pressed into molds, was fired once to
obtain a brown or buff body, then dipped in glaze composed of lead and tin oxide with a
silicate of potash. The opaque glaze presented a surface that was suitable to receive
decoration. A second firing after decoration fixed the white glaze to the body and the
pigments to the glaze, so that the colors became permanently preserved. Frequently, the
beauty of these wares was increased by dipping them in a translucent lead glaze
composed of oxide of lead mixed with sand, potash, and salt. When certain luster
pigments and enamels were used in all-over painting, wares had to be specially fired at
low temperature. Application of metallic luster pigments required great skill because
these colors were extremely volatile and needed special handling.

Luca della Robbia (see della Robbia, family) did not, as has been held, invent the
enamel tin-glazing process; nevertheless, his work raised majolica production from a
craft to high art in Italy. Not only did he use blue and white enamels in decorative work,
but, as a sculptor, he also used the majolica technique to add brilliance to the surface of
his productions. By the beginning of the 15th century Italian potters had abandoned the
old familiar processes, and a revolution in style and techniques was under way. The
severe style as followed principally in the school of Tuscany continued to the end of the
15th century, but rules and principles slackened until the inclusion of human figures in
designs, previously frowned upon, was accepted. At the end of the 15th century Faenza
became the thriving center of a reinvigorated pottery industry in Italy. A new, rich
decorative style, known as istoriato, fired the imagination of potters, reaching its zenith
in the workshops of Urbino.

In early 17th-century England, attractive slipwares were produced, including the slip-
decorated earthenware that was a speciality of the Toft family of potters. A kind of tin-
glazed earthenware was also produced in the Netherlands, principally at Delft,
beginning in the mid-17th century. Termed delftware, it was among the first European
wares to be decorated with motifs inspired by Chinese and Japanese models.

Continental Porcelains

Eventually, European potters, who much admired the porcelain of the Far East,
attempted to imitate it, but the formula remained elusive. Francesco de Medici, grand
duke of Tuscany, produced an inferior type of soft-paste porcelain in his Florence
workshop during the 16th century. In March 1709, Augustus II of Saxony announced
that his ceramist Johann Bottger (1682-1719) had discovered how to make porcelain.
The first European royal porcelain manufactory was consequently established at
Meissen (see Meissen ware) near Dresden, Germany. Throughout the century following
the discovery of the porcelain formula--when, despite the utmost precautions at
Meissen, the secret leaked out--many rival factories were set up in Europe. Germany,
Austria, Italy, France, and England soon had factories engaged in the production of
wares much like those of Meissen.

Porcelain figures were first produced in Meissen as table ornaments; the earliest
examples were formed as part of sweetmeat dishes. Many splendid wares issued from
the royal factory, but none were more admired than the finely modeled and decorated
porcelain figures imitated by almost every German, Austrian, Italian, and English
factory of note. Widespread interest in figures of both pottery and porcelain has
continued to the present. Johann Joachim Kandler (1706-75), a master modeler, was the
most notable of the artisans engaged in this work at Meissen and rivaled the famous
Franz Anton Bustelli (1723-63) of Nymphenburg (see Nymphenburg ware).

The methods used to produce porcelain figures as developed by Kandler imparted a new
dimension to the art. German porcelain figures were usually produced from molds,
which, in turn, were cast from an original master model made of wax, clay, or,
occasionally, wood. The use of molds facilitated unlimited reproduction. Because the
figures shrank during firing, allowances had to be made in their sizes; they were also
provided with a small venthole in the back or base to permit excess heated air to escape.
Because different factories placed these holes differently, their positions help determine
the provenance and authenticity of given pieces. When considerable undercutting was
necessary, porcelain figures were usually made in sections, using separate molds.
Portions of elaborate groups and single figures were later joined by a specially trained
assembler (known as a "repairer") who usually worked from a master model.

Europe's second hard-paste porcelain factory began operations at Vienna in 1717. In the
late 1700s at the royal Sevres (see Sevres ware) factory in France, potters experimented
until they developed a remarkably white, finely textured body. Sevres wares were
painted in unique colors that no other European factory could duplicate. The bleu de roi
and rose Pompadour of Sevres wares captivated all Europe and, with the products of
Meissen and Vienna, inspired English potters.

English Wares

The finest English porcelain--both soft- and hard-paste--was made between about 1745
and 1775. The first English porcelain was probably produced at Chelsea (see Chelsea
ware) under Charles Gouyn, but his successor Nicholas Sprimont, a Flemish silversmith
who took over management in 1750, was responsible for the high-quality wares,
especially the superb figures, for which the factory became famous. Factories at
Worcester (see Worcester ware), Bow, and Derby also produced wares that rival those
of the Continent.

Led by the ambitious, energetic, and enterprising Josiah Wedgwood and his successors
at the Etruria factory, English potters in the late 18th and early 19th centuries became
resourceful and inventive. Wedgwood's contributions consisted mainly of a much
improved creamware, his celebrated jasperware, so-called black basalt, and a series of
fine figures created by famous modelers and artists. After Wedgwood, other potters of
the first half of the 19th century developed a number of new wares. Of these, Parian
ware was the most outstanding and commercially successful.

The name of this ware was derived from Paros, the Greek island from which sculptors
in ancient times obtained the creamy or ivory-tinted marble that Parian ware resembled.
The first examples of this new product, described as "statuary porcelain," issued from
Copeland and Garret's factory in 1842 and were immediately acclaimed. Two varieties
of Parian ware were produced: statuary parian, used in the making of figures and
reproductions of sculpture, and hard-paste, or standard, parian, from which hollowware
was made. Statuary parian, incorporating a glassy frit, is classified as soft porcelain.
Standard parian, with a greater proportion of feldspar in the composition but no frit, is
hard porcelain. Early parian statuary was ivory-tinted due to the presence of iron in the
feldspar devoid of iron silicate. Suitable deposits were eventually located in Sweden and
Ireland. Both English and American potters either obtained details of the original
formula or worked out their own, and the resulting production of Parian wares on both
sides of the Atlantic was enormous.

Among the most beautiful and successful wares invented by 19th-century potters were
those decorated in what came to be known in England as pate-sur-pate, a paste-on-paste
technique devised sometime after 1870 by Marc-Louis Solon (1835-1913) of Minton's
in England. Pate-sur-pate, involving both modeling and painting techniques, was stained
Parian ware decorated with reliefs in translucent tinted or white slip, the colors being
laid one upon the other. Solon was inspired by a Chinese celadon case decorated with
embossed flowers that he had admired in the museum at Sevres, where he worked for a
time. At first his slip painting on biscuit porcelain simply peeled off; he was successful,
however, when he applied layers of slip to a damp surface. Minton wares decorated with
pate-sur-pate became the most costly and coveted ceramic ornaments produced in
England in the last quarter of the 19th century. Only a few English potters mastered
Solon's complex technique, although the work of his pupil, Alboin Birks, rivaled that of
the master.

20th-Century Developments

By the late 19th century, with the development of machinery and the introduction of
new technologies, the age of mass production dawned and the potter's art consequently
suffered. Western ceramic wares declined markedly in quality of materials and
decoration. Florid designs, gaudy coloring, and inartistic shapes became fashionable,
and the resulting decadence continued into the 20th century. Not until the 1930s were
signs of revival in the form and decoration of ceramics discernible, principally in the
productions of artist-potters who were active in Western Europe and the United States.
Many of these artist-potters arrived at their innovations by way of continuous
experiment with materials and techniques. Others sought inspiration from primitive
types of Japanese pottery or in the forms of ancient American Indian traditions. Since
the end of World War II, the design and decoration of ceramics in both Europe and the
United States, especially ornamental wares, has been largely influenced by individual
artist-artisans. Commercial products, such as tablewares, have tended to reflect the
styles and patterns developed by these potters, whose work has often shown striking
originality.
Various Applications of Ceramics
Ceramics, pronounced suh RAM ihks, are one of the three most important types of
engineering materials that are primarily synthetic. The other two are metals and plastics.
Ceramics include such everyday materials as brick, cement, glass, and porcelain. They
also include unusual materials used in electronics and spacecraft. Most ceramics are
hard and can withstand heat and chemicals. These properties give them a variety of uses
in industry. Artists also create ceramics. This article discusses the use of ceramics in
industry. For information on how artists make ceramics, see POTTERY.

Properties of ceramics.

Manufacturers make common ceramics from such minerals as clay, feldspar, silica, and
talc. These minerals, called silicates, form most of the earth's crust. Clay is an important
silicate. But it is not used in all ceramic materials. Glass, for example, is made from
sand. Chemists make materials called advanced ceramics in the laboratory from
compounds other than silicates. These compounds include alumina, silicon carbide, and
barium titanate.

Most ceramic products, like their mineral ingredients, can withstand acids, gases, salts,
water, and high temperatures. But not all ceramic products have the same properties.
Common ceramics are good insulators--that is, they conduct electricity poorly.
However, certain ceramics lose their electrical resistance and become superconductors
when they are cooled (see SUPERCONDUCTIVITY). Some ceramic materials are
magnetic. Engineers control the properties of ceramics by controlling the proportion and
type of materials used.

Kinds of ceramic products:

The properties of ceramics make them especially suitable for certain products. Products
made of ceramic materials include abrasives (materials used for grinding), construction
materials, dinnerware, electrical equipment, glass products, and refractories (heat-
resistant materials).

Abrasives: Manufacturers use some extremely hard ceramic materials for cutting metals
and for grinding, polishing, and sanding various surfaces. These ceramic materials
include alumina and silicon carbide.

Construction materials: Clay and shale are used in making strong, durable bricks and
drainpipes for homes and other buildings. Tiles are made of clay and talc. Cement
consists chiefly of calcium silicates and is used primarily in making concrete. Gypsum
is used to produce plaster for the surfaces of walls and ceilings. Bathtubs, sinks, and
toilets are made of porcelain, which consists chiefly of clay, feldspar, and quartz.

Dinnerware: Ceramics make excellent containers for food and drinks. They do not
absorb liquids, and they resist acids, salts, detergents, and changes in temperature. Most
ceramic dinnerware is made from a mixture of clays, feldspar, and quartz.
Electrical equipment: Ceramics that do not conduct electricity are used as insulators in
automobile spark plugs, on electric power lines, and in television sets. Such ceramics
include alumina and porcelain. Another ceramic material, barium titanite, is used in
making capacitors, which store electric charges in electronic equipment. Magnetic
ceramics are used in electronic circuits and in electric motors. Complex electronic
circuits are bonded on thin layers of alumina.

Glass products: Glass is one of the most important materials, chiefly because of its
transparency. Products made of glass include food containers, light bulbs, windows, and
lenses for eyeglasses and telescopes. Fiberglass insulates the walls of many homes.
Cables made of glass fibers transmit telephone calls and other information. The main
ingredient in glass is silica.

A glasslike coating called porcelain enamel serves as a protective surface on many
metal products. These products include such appliances as refrigerators, stoves, and
washing machines. Porcelain enamel also makes outdoor signs weather-resistant.

Refractories: The property of heat-resistance makes refractories suitable for the
manufacture of industrial boilers and furnaces, such as the furnaces used to make steel.
Refractories shaped into tiles cover the surface of space shuttles, which must withstand
the intense heat created by high speeds. Ceramics used in making refractories include
alumina, magnesium oxide, silica, silicon carbide, and zirconium oxide.

Other products: Ceramic engineers continually develop new uses for ceramics. For
example, porcelain is used to make false teeth and artificial bone joints. Uranium oxide
ceramics serve as fuel elements for nuclear reactors. Cutting tools are made from silicon
nitride. Refractories made from carbides are used to make parts for aircraft engines.
Alumina is used in making certain types of lasers (instruments that produce intense light
beams).

Making ceramics.

The clays and other minerals used in ceramics are dug from the earth and refined to
improve their purity. Machines crush and grind the materials into fine particles. The
particles are mixed in the proper proportion, and water or other liquid is added to
produce a mixture that can be shaped. A gluelike substance is sometimes added to
mixtures that do not contain clay. Glass and some refractory products are made by
melting the particles and shaping them when they are molten.

The most common methods for shaping clay ceramics are slip casting, jiggering,
extrusion, and pressing. In slip casting, the liquid mixture is poured into a mold that
absorbs water. As the water is absorbed, a layer of ceramic particles is deposited onto
the mold, forming such hollow items as teapots and vases. The excess liquid is then
poured out of the mold. In jiggering, a machine presses the clay onto a rotating mold.
Jiggering is used to make dinnerware. Extrusion shapes items into rods or tubes by
forcing ceramic paste through a shaping tool called a die. In pressing, ceramic powder is
pressed in a steel die or a rubber mold.

After the product has dried, it is strengthened by firing, a process that takes place in
special furnaces called kilns. Ceramics are fired at temperatures ranging from about
1200 to 3000 _F (649 to 1649 _C). Firing hardens the product permanently and gives it
strength, durability, and other desired qualities.

Manufacturers cover many ceramic products with a glassy coating called glaze. Glaze
prevents the item from absorbing liquids and makes it smoother and easier to clean.
Glazes are also used for decoration.

History.

Pottery, the oldest form of ceramic products, dates back to prehistoric times. Examples
of pottery about 13,000 years old have been found in several parts of the world.

Industrial uses of ceramics began in the 1900's. Military requirements of World War II
(1939-1945) created a need for high-performance materials and helped speed the
development of ceramic science and engineering. During the 1960's and 1970's,
advances in atomic energy, electronics, communications, and space travel required new
kinds of ceramics. For example, the introduction of high-speed spacecraft required heat-
resistant ceramic coatings and engine linings. Since the early 1980's, researchers have
worked to develop ceramic engines for cars, trucks, pumps, and electric generators. The
discovery of ceramic superconductors in 1986 has spurred intense worldwide research
to develop superconducting ceramic parts for electronic devices, electric motors, and
transportation equipment.
Ceramics in Manufacturing
Materials made of clay are among the most ancient manufactured articles and have
played a vital role in human civilization. Although clay, as a ceramic material, is still
widely used, modern ceramics include a wide range of nonorganic, nonmetallic
materials whose manufacture requires heating at high temperatures. Important ceramics
products include brick and tile, clay pipe, refractory brick, pottery and porcelain articles
and enamels, ferrites in computer memories, barium titanate and alumina in electronics,
uranium dioxide as nuclear fuel, and garnets in lasers. Glass and cement are also major
ceramic materials

The raw materials used to make ceramics are inexpensive and widely available, and
include clay, feldspar, quartz sand, iron oxides, and alumina. Clay is made up of fine,
platelike crystals of hydrated aluminosilicates. The crystals are usually from about 1 to
10 microns (.001 to .010 mm) in their longest dimension. A thin film of water binds the
crystals together and with their platelike shape gives the clay its easy working
properties. The platelike form of clay crystals reflects the molecular layer structure of
the silicon-oxygen and aluminum-oxygen groups in the clay compounds.

CERAMICS MANUFACTURE

Dust Press Method:

Most American manufacturers use the press method for forming tile. Powdered raw
materials are mixed with water or other binding liquids, and are formed by a hydraulic
press. The clay is usually pressed damp, with about 10 percent water, into dies or molds
under moderate pressures. Ceramics made of purified powders such as alumina and
ferrites are pressed dry at higher pressure with an organic binder (for example, 1 percent
polyvinyl alcohol). In isostatic pressing, the powder is held in a rubber mold, and the
pressure is applied with a fluid such as glycerine giving uniform pressure throughout the
sample, with less warping and fewer defects. Samples in bar, rod, or tube form can be
extruded through a die. The fired bisque, or clay body can absorb water, and is generally
regarded as a "soft" tile, another common name of this type of tile is whiteware.

Hand Made tile - Slip casting:

In slip casting, a suspension of ceramic powder, usually in water, is poured into a mold
made of plaster of paris. Water is absorbed by the mold, and a hard lining on the mold
wall is built up; excess liquid is poured out of the mold. Using slip casting, a number of
complex shapes can be made economically, since the cost of the molds is low. These
tiles are also considered soft.

After forming, the ceramic ware must be carefully heated for a few hours at about 100
degrees-200 degrees C (about 200 degrees-400 degrees F) to remove excess water or
binder. The rate of drying must be carefully controlled so that warping and defects do
not form as the sample shrinks. After drying, the article is fired at a high temperature
(800 degrees-2000 degrees C/1500 degrees-3500 degrees F) to sinter or bind together
the individual crystals of the ceramic powder into a solid, coherent mass. The higher the
firing temperature, the more dense and less porous the material becomes. A wide range
of properties in ceramics is possible with different firing temperatures and times.

IMPORTANT CERAMIC CATEGORIES

The most common ceramic articles of pottery, porcelain, brick, and pipe form complex
mixtures of several different solid phases after firing. Traditional whitewares and
porcelains contain at least three starting materials--clay, feldspar, and silica sand. When
a mixture of these materials is heated at high temperatures (above 1200 degrees C/2200
degrees F), the feldspar (potassium-sodium aluminosilicate) melts and coats the clay
and sand crystals. As firing proceeds, tightly bound water in the clay structure is
removed, and fine, needlelike crystals of an aluminosilicate called mullite are formed
from the clay. The grains of silica sand are partly dissolved in the viscous liquid
feldspar. In the cooled structure there is a glassy phase from the liquid feldspar that
binds together the sand grains and mullite crystals. This glassy phase may also give the
ware a smooth, polished surface.

Firing at an intermediate temperature (about 1100 degrees C/2000 degrees F) produces
stoneware, a heavy, opaque ceramic, nonporous and glazed. At lower firing
temperatures (less than 1000 degrees C/1832 degrees F), a more porous ware with a
rough surface results and is usually called earthenware. To make fine, translucent
porcelain requires a higher firing temperature (up to 1400 degrees C/2500 degrees F) so
that more glass is formed.

NEW CERAMICS APPLICATIONS

"High technology" ceramics are new types of materials that surpass earlier ceramics in
strength, hardness, light weight, or improved heat resistance. For example, ceramic
powders can now be made from particles of absolutely uniform size. When sintered,
these powders produce ceramics that are far less vulnerable to fracture or thermal shock
than ordinary ceramics. Added to a matrix of metal or ceramic, thin ceramic fibers
increase the tensile strength of the material (see composite material).

Barium titanate has a high dielectric constant and consequently is used in capacitors. It
is also strongly piezoelectric (see piezoelectricity), which means that it develops an
electrical voltage when stressed in a particular crystallographic direction. It is used in
microphones, phonograph pickups, strain gauges, and ultrasonic devices.

The apatites are a family of calcium phosphate minerals that have been widely used as
phosphors in fluorescent lamps. Special impurities in the apatite--such as manganese--
fluoresce and thereby change the ultraviolet light of a mercury arc into visible light. In a
lamp this change increases the output of visual radiation for a given input.
Hydroxylapatite is a bone mineral, and has recently been developed as a bone and tooth
implant material.

The most convenient form of nuclear fuel is uranium dioxide. Uranium ores are reacted
and purified to form uranium dioxide, which is then sintered into pellets that serve as
nuclear fuel. The pellets are packed into long tubes and are especially stable even with
the severe radiation and thermal conditions they encounter.
Beta-alumina (a compound of 1 part sodium oxide with 11 parts aluminum oxide) has
been traditionally used as a refractory material; recently it was found to have high
electrical conductivity at low temperatures. This conductivity results from high mobility
of the sodium ions, and beta-alumina is being used as an electrolyte in high-temperature
batteries. The beta-alumina separates liquid sodium and a liquid sulfur-sodium
polysulfide mixture; as the battery is charged or discharged, the sodium ions in the
electrolyte transfer charge from one liquid to another. This battery is highly efficient
and should find application in electric vehicles and for storage of electric power during
off-peak hours.

Ceramics have proven to be ideal hosts for the fluorescent ions needed in lasers. Ruby,
which is alumina containing some chromium impurity, is one of the most used laser
materials, and garnets are also excellent laser hosts.

Amorphous ceramics are produced by firing ceramic material for a short time at low
temperatures, to produce substances that lack the usual crystalline ceramic structure.
Like plastics, these ceramics can be sprayed onto surfaces or injection-molded before
they are fired. They are used to make complex shapes and thin ceramic films.

Ultrahard ceramic layers are built into the steel in tank bodies. When a projectile
penetrates a layer, it pulverizes the ceramic, breaking the bonds that bind the molecules
together. This chemical change causes the ceramic fragments to expand. In expanding,
they grind up the softer material of the projectile, making it inoperative.

Ceramic fibers combined with epoxy glues produce a composite fabric that is
lightweight but stronger than steel. It is currently used in making small airplane bodies.
A History of Porcelain
Porcelain, pronounced POUR suh lihn, is a type of ceramics highly valued for its beauty
and strength. It is often called china, or chinaware, because it was first made in China.
Porcelain is characterized by whiteness, a delicate appearance, and translucence (ability
to let light through). Because it is the hardest ceramic product, porcelain is used for
electrical insulators and laboratory equipment. However, porcelain is known primarily
as a material for high-quality vases and tableware, as well as for figurines and other
decorative objects. The type of porcelain that is used for such purposes produces a bell-
like ring when struck.

Porcelain differs from other types of ceramics in its ingredients and in the process by
which it is produced. Two common types of ceramics--earthenware and stoneware--are
made from a single natural clay, which is then fired (baked). In many cases, the object is
coated with a glassy substance called glaze. Firing at a low temperature produces
earthenware, a porous material. Earthenware can be made waterproof by glazing. Firing
at a high temperature produces stoneware, a hard, heavy material. Stoneware is
nonporous without glazing.

Unlike earthenware and stoneware, porcelain is basically made from a mixture of two
ingredients--kaolin and petuntse. Kaolin is a pure white clay that forms when the
mineral feldspar breaks down. Petuntse is a type of feldspar found only in China. It is
ground to a fine powder and mixed with kaolin. This mixture is fired at temperatures
from about 2280 _F (1250 _C) to 2640 _F (1450 _C). At these extreme temperatures,
the petuntse vitrifies--that is, it melts together and forms a nonporous, natural glass. The
kaolin, which is highly resistant to heat, does not melt and therefore allows the item to
hold its shape. The process is complete when the petuntse fuses itself to the kaolin.

Kinds of porcelain

There are three main kinds of porcelain: (1) hard-paste porcelain, (2) soft-paste
porcelain, and (3) bone china. The differences between these types of porcelain are
based on the material from which they are made. This material is called the body or
paste.

Hard-paste porcelain, which is sometimes called true porcelain or natural porcelain, has
always been the model and ideal of porcelain makers. It is the type of porcelain first
developed by the Chinese from kaolin and petuntse. Hard-paste porcelain resists
melting far better than other kinds of porcelain. For this reason, it can be fired at higher
temperatures. These hot temperatures cause the body and the glaze to become one.
When hard-paste porcelain is broken, it is impossible to distinguish the body from the
glaze.

The proportions of kaolin and petuntse in hard-paste porcelain may vary. The porcelain
is said to be severe if the percentage of kaolin is high, and mild if the percentage of
kaolin is low. Most collectors of porcelain prefer mild porcelain because of its mellow,
satiny appearance. In comparison, severe porcelain may seem harsh and cold.
Soft-paste porcelain, sometimes called artificial porcelain, was developed in Europe in
an attempt to imitate Chinese hard-paste porcelain. Experimenters used a wide variety
of materials in their efforts to produce a substance that was hard, white, and translucent.
They eventually developed soft-paste porcelain by using mixtures of fine clay and
glasslike substances. These materials melt at the high temperatures used in making
hard-paste porcelain. For this reason, soft-paste porcelain is fired at lower temperatures
and does not completely vitrify--that is, it remains somewhat porous. Breaking a piece
of soft-paste porcelain reveals a grainy body covered with a glassy layer of glaze.

Although soft-paste porcelain was invented in imitation of true porcelain, it has merits
of its own. Most of it is creamy in tone, and some people prefer this color to pure white.
In addition, the colors used to decorate it merge with the glaze to produce a soft, silky
effect that appeals to many collectors.

Bone china is basically made by adding bone ash (burned animal bones) to kaolin and
petuntse. English porcelain makers discovered this combination of ingredients about
1750, and England still produces nearly all the world's bone china. Though not as hard
as true porcelain, bone china is more durable than soft-paste porcelain. The bone ash
greatly increases the translucence of the porcelain.

Decorating porcelain

A piece of porcelain is shaped on a potter's wheel or in a mold. After this stage, the
porcelain worker may decorate it by (1) surface modifications, (2) painting, or (3)
transfer printing.

Surface modifications are achieved by incising (carving), perforating (poking holes),
and embossing (applying raised designs). A well-known method of embossing porcelain
is to apply a mixture of water and clay, called slip, to the item with a brush. Relief
designs (three-dimensional effects) are usually molded separately and then attached to
the porcelain.

Painting the porcelain surface may be done in several ways. One method is to use a
colored glaze, such as the famous Chinese celadon. This glaze is a soft gray-green color.
Another type of decoration is underglaze (designs painted on a piece before it is glazed).
A deep blue made from the metal cobalt is the most dependable color used for
underglazing. Cobalt blue has been widely used both in China and in Europe.

Paints that are applied over the glaze are commonly called enamels. A large variety of
enamel colors were perfected at an early period. Most of them are made from metallic
oxides, such as iron, copper, and manganese. Enamel colors require a second firing to
make them permanent.

Porcelain painting in Europe differed greatly from porcelain painting in China. Chinese
decorators separated each color from the next with a dark outline, but European artists
blended colors together with no separating line. In addition, Europeans used decorations
purely for their artistic value, but Chinese decorations were symbolic. For example, a
pomegranate design symbolized a wish for many offspring because a pomegranate has
many seeds.
Transfer printing revolutionized the porcelain industry in 1756 by enabling workers to
decorate wares much faster than they could by hand. In this process, a design is
engraved on a copper plate, inked with ceramic color, and transferred to tissue paper.
While the color is still wet, the tissue paper is pressed against a porcelain object, leaving
the design on its surface.

History of porcelain

Oriental porcelain. The Chinese probably made the first true porcelain during the Tang
dynasty (618-907). The techniques for combining the proper ingredients and firing the
mixture at extremely high temperatures gradually developed out of the manufacture of
stoneware. During the Song dynasty (960-1279), Chinese emperors started royal
factories to produce porcelain for their palaces. Since the 1300's, most Chinese
porcelain has been made in the city of Jingdezhen.

For centuries, the Chinese made the world's finest porcelain. Collectors regard many
porcelain bowls and vases produced during the Ming dynasty (1368-1644) and Qing
dynasty (1644-1912) as artistic treasures. Porcelain makers perfected a famous blue and
white underglazed procelain during the Ming period. Painting over the glaze with
enamel colors also became a common decorating technique at this time. During the
Qing period, the Chinese developed a great variety of patterns and colors and exported
porcelain objects to Europe in increasing numbers.

By the 1100's, the secret of making porcelain had spread to Korea and to Japan in the
1500's. Workers in these countries also created beautiful porcelain objects. A Japanese
porcelain called Kakiemon was first produced during the 1600's. It features simple
designs on a white background. Another well-known Japanese porcelain called Imari
ware, or Arita, is famous for its dense decorations in deep blue and red.

European porcelain. As early as the 1100's, traders brought Chinese porcelain to
Europe, where it became greatly admired. However, it was so rare and expensive that
only wealthy people could afford it.

As trade with the Orient grew during the 1600's, porcelain became popular with the
general public. The custom of drinking tea, coffee, and chocolate became widespread
and created a huge demand for porcelain cups and saucers. European manufacturers
responded by trying to make hard-paste porcelain themselves, but for a long time they
failed to discover the secret. Nevertheless, some of their experiments resulted in
beautiful soft-paste porcelain. The first European soft-paste porcelain was produced in
Florence, Italy, about 1575.

By the 1700's, porcelain manufactured in many parts of Europe was starting to compete
with Chinese porcelain. France, Germany, Italy, and England became the major centers
for European porcelain production.

French porcelain. France became famous during the 1700's as the leading producer of
soft-paste porcelain. The first factories were established at Rouen, St. Cloud, Lille, and
Chantilly.
The most celebrated type of soft-paste porcelain was first produced at Vincennes in
1738. In 1756, the factory was moved to the town of Sevres. Its soft-paste porcelain
became known as Sevres. The earliest Sevres had graceful shapes and soft colors.
Sevres pieces produced from 1750 to 1770 were decorated with brilliant colors and
heavy gilding. Many of these pieces had richly colored backgrounds and white panels
painted with birds, flowers, landscapes, or people. Sevres is also noted for its fine
figurines of biscuit (unglazed porcelain).

Beginning in 1771, a hard-paste porcelain industry developed near Limoges, where
kaolin deposits had been discovered. By the 1800's, Limoges had become one of the
largest porcelain centers in Europe. An American named David Haviland opened a
porcelain factory at Limoges in 1842 to make tableware for the American market.
Haviland porcelain features soft colors that blend together and small floral patterns.

German porcelain. A German chemist named Johann Friedrich Bottger discovered the
secret of making hard-paste porcelain in 1708 or 1709. This discovery led to the
establishment of a porcelain factory in Meissen in 1710. Meissen porcelain is
sometimes called Dresden because Bottger first worked near the city. For nearly a
century, it surpassed in quality all other hard-paste porcelain made in Europe.

The great success of Meissen porcelain can be partly attributed to the fine artists who
decorated it. They painted the wares with an amazing variety of colors and designs.
Johann Horoldt (or Herold), who became chief painter in 1720, produced beautiful
Chinese and Japanese as well as European designs. Johann Kandler, who worked from
about 1730 to 1770, is famous for his exquisite figures of animals and people.

Political disorder in Germany and competition from Sevres porcelain drove the Meissen
factory into decline during the late 1700's. It continued to operate but did not make
wares of the same artistic quality.

English porcelain. England is well known as the center for the production of bone
china. Before the invention of bone china, the English manufactured fine soft-paste
porcelain at Chelsea, Bow, and Derby. Most of this English porcelain was styled after
Oriental and Continental designs.

Worcester porcelain, first produced in 1751, is one of the oldest and best English
porcelains. During its early years, the Worcester factory produced soft-paste porcelain,
much of it decorated with Chinese designs in blue underglaze. Since the 1760's, it has
manufactured bone china in a wide variety of colors and patterns.

				
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