Pottery is the
ceramic ware
made by potters. Major types of pottery include
earthenware,
stoneware,
and
porcelain. The places where such wares
are made are called potteries. Pottery is one of the oldest human
technologies and art-forms, and remains a major industry today.
Ceramic art covers the art of pottery,
whether in items made for use or purely for decoration.
Background
Pottery is made by forming a
clay
body into objects of a required shape and heating them to high
temperatures in a
kiln to induce reactions that
lead to permanent changes, including increasing their strength and
hardening and setting their shape. There are wide regional
variations in the properties of clays used by potters and this
often helps to produce wares that are unique in character to a
locality. It is common for clays and other minerals to be mixed to
produce clay bodies suited to specific purposes.
Prior to some shaping processes, air trapped within the clay body
needs to be removed. This is called de-airing and can be
accomplished by a machine called a vacuum pug or manually by
wedging. Wedging can also help
to ensure an even moisture content throughout the body. Once a clay
body has been de-aired or wedged, it is shaped by a variety of
techniques. After shaping it is dried before firing. There are a
number of stages in the drying process.
Leather-hard
refers to the stage when the clay object is approximately 75-85%
dry. Clay bodies at this stage are very firm and only slightly
pliable. Trimming and handle attachment often occurs at the
leather-hard state. Clay bodies are said to be "bone-dry" when they
reach a moisture content at or near 0%. Unfired objects are often
termed
greenware. Clay bodies at this stage are very
fragile and hence can be easily broken.
Methods of shaping
The potter's most basic tool is the
hand.
However, many additional tools have been developed over the long
history of pottery manufacturing, including the
potter's wheel and turntable, shaping tools
(paddles, anvils, ribs), rolling tools (roulettes, slab rollers,
rolling pins), cutting/piercing tools
(knives, fluting tools, wires) and finishing tools (burnishing
stones, rasps, chamois).
Pottery can be shaped by a range of methods that include:
Handwork or hand building. This is the earliest
and the most individualized and direct forming method. Wares can be
constructed by hand from coils of clay, from flat slabs of clay,
from solid balls of clay — or some combination of these. Parts of
hand-built vessels are often joined together with the aid of
slurry or slip, a runny mixture of clay and
water. Hand building is slower and more gradual than
wheel-throwing, but it offers the potter a high degree of control
over the size and shape of wares. While it isn't difficult for an
experienced potter to make identical pieces of hand-built pottery,
the speed and repetitiveness of wheel-throwing is more suitable for
making precisely matched sets of wares such as
table wares. Some
studio potters find hand building more
conducive to fully using the imagination to create one-of-a-kind
works of
art, while others find this with the
wheel.
A potter shapes a piece of pottery on
an electric-powered potter's wheel
The potter's wheel. In the process that is called
"throwing" (coming from the
Old English
word
thrawan, which means to twist or turn ) , a ball of
clay is placed in the center of a turntable, called the wheel-head,
which the potter rotates with a stick, or with foot power (a kick
wheel or
treadle wheel) or with a variable
speed
electric motor. (Often, a disk
of plastic, wood or plaster — called a
bat — is first set
on the wheel-head, and the ball of clay is thrown on the bat rather
than the wheel-head so that the finished piece can be removed
intact with its bat, without distortion.)
During the process of throwing the wheel rotates rapidly while the
solid ball of soft clay is pressed, squeezed, and pulled gently
upwards and outwards into a hollow shape. The first step, of
pressing the rough ball of clay downward and inward into perfect
rotational symmetry, is called
centering the clay, a most important (and often most
difficult) skill to master before the next steps:
opening
(making a centered hollow into the solid ball of clay),
flooring (making the flat or rounded bottom inside the
pot),
throwing or
pulling (drawing up and shaping
the walls to an even thickness), and
trimming or
turning (removing excess clay to refine the shape or to
create a
foot).
From around 7th century BC until the introduction of
slip casting in the
18th century AD, the potter's wheel was the most effective method
of
mass producing pottery, although
it is also often employed to make individual pieces. Wheel-work
makes great demands on the skill of the potter, but an accomplished
operator can make many near-identical plates, vases, or bowls in
the course of a day's work. Because of its inherent limitations,
wheel-work can only be used to create wares with
radial symmetry on a
vertical axis. These can then be altered by
impressing, bulging,
carving,
fluting,
faceting,
incising, and by other methods making the
wares more visually interesting. Often, thrown pieces are further
modified by having handles, lids, feet, spouts, and other
functional aspects added using the techniques of handworking.
Jiggering and jolleying: These operations
are carried out on the potter's wheel and allow the time taken to
bring wares to a standardized form to be reduced.
Jiggering is the operation of bringing a shaped tool into
contact with the plastic clay of a piece under construction, the
piece itself being set on a rotating plaster mould on the wheel.
The jigger tool shapes one face whilst the mould shapes the other.
Jiggering is used only in the production of flat wares, such as
plates, but a similar operation,
jolleying, is used in the
production of hollow-wares, such as cups. Jiggering and jolleying
have been used in the production of pottery since at least the 18th
century. In large-scale factory production jiggering and jolleying
are usually automated, which allows the operations to be carried
out by semi-skilled labor.
Roller-head
machine: This machine is for shaping wares on a
rotating mould, as in jiggering and jolleying, but with a rotary
shaping tool replacing the fixed profile. The rotary shaping tool
is a shallow cone having the same diameter as the ware being formed
and shaped to the desired form of the back of the article being
made. Wares may in this way be shaped, using relatively unskilled
labor, in one operation at a rate of about twelve pieces per
minute, though this varies with the size of the articles being
produced. The roller-head machine is now used in factories
worldwide.
RAM pressing: A
factory process for shaping table wares and decorative ware by
pressing a bat of prepared clay body into a required shape between
two porous molding plates. After pressing, compressed air is blown
through the porous mould plates to release the shaped wares.
Granulate pressing: As the name suggests, this is
the operation of shaping pottery by pressing clay in a semi-dry and
granulated condition in a
mould.
The clay is pressed into the mould by a porous die through which
water is pumped at high pressure. The
granulated clay is prepared by
spray-drying to produce a fine and free flowing material having a
moisture content of between about five and six per cent. Granulate
pressing, also known as
dust pressing, is widely used in
the manufacture of
ceramic tiles and,
increasingly, of plates.
Slipcasting: is often
used in the mass-production of ceramics and is ideally suited to
the making of wares that cannot be formed by other methods of
shaping. A
slip, made by mixing
clay body with water, is poured into a highly
absorbent plaster mold. Water from the slip is absorbed into the
mould leaving a layer of clay body covering its internal surfaces
and taking its internal shape. Excess slip is poured out of the
mold, which is then split open and the molded object removed.
Slipcasting is widely used in the production of sanitary wares and
is also used for making smaller articles, such as
intricately-detailed figurines.
Decorating and glazing
Pottery may be decorated in a number of ways, including:
Additives can be worked into the clay body prior
to forming, to produce desired effects in the fired wares. Coarse
additives, such as sand and
grog (fired
clay which has been finely ground) are sometimes used to give the
final product a required texture. Contrasting colored clays and
grogs are sometimes used to produce patterns in the finished wares.
Colorants, usually metal oxides and carbonates, are added singly or
in combination to achieve a desired color. Combustible particles
can be mixed with the body or pressed into the surface to produce
texture.
Agateware: So-named after
its resemblance to the quartz mineral
agate
which has bands or layers of color that are blended together.
Agatewares are made by blending clays of differing colors together,
but not mixing them to the extent that they lose their individual
identities. The wares have a distinctive veined or
mottled appearance.
The term 'agateware'
is used to describe such wares in the United Kingdom
; in Japan the term neriage is used and in
China
, where such things have been made since at least
the Tang Dynasty, they are called
marbled wares. Great care is required in the
selection of clays to be used for making agatewares as the clays
used must have matching thermal movement characteristics.
Banding: This is the application, by hand or by
machine, of a band of color to the edge of a plate or cup. Also
known as lining, this operation is often carried out on a potter's
wheel.
Burnishing: The surface of
pottery wares may be
burnished prior to firing by rubbing
with a suitable instrument of wood, steel or stone, to produce a
polished finish that survives firing. It is possible to produce
very highly polished wares when fine clays are used, or when the
polishing is carried out on wares that have been partially dried
and contain little water, though wares in this condition are
extremely fragile and the risk of breakage is high.
Engobe: This is a
clay slip, often white or cream in color
that is used to coat the surface of pottery, usually before firing.
Its purpose is often decorative, though it can also be used to mask
undesirable features in the clay to which it is applied. Engobe
slip may be applied by painting or by dipping, to provide a
uniform, smooth, coating. Engobe has been used by potters from
pre-historic times until the present day, and is sometimes combined
with
sgraffito decoration, where a layer
of engobe is scratched through to reveal the color of the
underlying clay. With care it is possible to apply a second coat of
engobe of a different color to the first and to incise decoration
through the second coat to expose the color of the underlying coat.
Engobes used in this way often contain substantial amounts of
silica, sometimes approaching the composition
of a
glaze.
Litho: This is a commonly used abbreviation for
lithography, although the alternative
names of
transfer print or
decal are also common. These are used to apply designs to
articles. The litho comprises three layers: the color, or image,
layer which comprises the decorative design; the cover coat, a
clear protective layer, which may incorporate a low-melting glass;
and the backing paper on which the design is printed by screen
printing or lithography. There are various methods of transferring
the design while removing the backing-paper, some of which are
suited to machine application
Gold: Decoration with gold is used on some high
quality ware. Different methods exist for its application,
including:
- Best gold - a suspension of gold powder in essential
oils mixed with a flux and a mercury salt extended. This can be
applied by a painting technique. From the kiln the decoration is
dull and requires burnishing to reveal the full color
- Acid Gold – a form of gold
decoration developed in the early 1860s at the English
factory of
Mintons Ltd, Stoke-on-Trent
. The glazed surface is etched with diluted
hydrofluoric acid prior to
application of the gold. The process demands great skill and is
used for the decoration only of ware of the highest class.
- Bright Gold – consists of a solution of gold
sulphoresinate together with other metal resonates and a flux. The
name derives from the appearance of the decoration immediately
after removal from the kiln as it requires no burnishing
- Mussel Gold – an old method of gold decoration. It was
made by rubbing together gold leaf, sugar and salt, followed by
washing to remove solubles
Glazing
Glaze is a glassy coating applied to pottery, the
primary purposes of which include decoration and protection. Glazes
are highly variable in composition but usually comprise a mixture
of ingredients that generally, but not always, mature at kiln
temperatures lower than that of the pottery that it coats. One
important use of glaze is in rendering pottery vessels impermeable
to water and other liquids. Glaze may be applied by dusting it over
the clay, spraying, dipping, trailing or brushing on a thin
slurry composed of glaze minerals and water.
Brushing tends not to give an even covering but can be effective as
a decorative technique. The color of a glaze before it has been
fired may be significantly different than afterwards. 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. Special methods of glazing are sometimes carried out in the
kiln. One example is
salt-glazing, where
common salt is introduced to the kiln to
produce a glaze of mottled,
orange peel texture. Materials
other than salt are also used to glaze wares in the kiln, including
sulfur. In wood-fired kilns fly-ash from the fuel can produce
ash-glazing on the surface of wares, and
the use of an ash and clay mix can result in alkaline glazes, as
used in
Catawba Valley
Pottery in the eastern United States.
Firing
Firing produces irreversible changes in the body. It is only after
firing that the article can be called pottery. In lower-fired
pottery the changes include
sintering, the
fusing together of coarser particles in the body at their points of
contact with each other. In the case of porcelain, where different
materials and higher firing-temperatures are used the physical,
chemical and mineralogical properties of the constituents in the
body are greatly altered. In all cases the object of firing is to
permanently harden the wares and the firing regime must be
appropriate to the materials used to make them. As a rough guide,
earthenwares are normally fired at temperatures in the range of
about 1000 to 1200 degrees Celsius; stonewares at between about
1100 to 1300 degrees Celsius; and porcelains at between about 1200
to 1400 degrees Celsius. However, the way that ceramics mature in
the kiln is influenced not only by the peak temperature achieved,
but also by the duration of the period of firing. Thus, the maximum
temperature within a kiln is often held constant for a period of
time to
soak the wares, to produce the maturity required
in the body of the wares.
The atmosphere within a kiln during firing can affect the
appearance of the finished wares. An oxidising atmosphere, produced
by allowing air to enter the kiln, can cause the
oxidation of clays and glazes. A reducing
atmosphere, produced by limiting the flow of air into the kiln, can
strip oxygen from the surface of clays and glazes. This can affect
the appearance of the wares being fired and, for example, some
glazes containing
iron fire brown in an
oxidising atmosphere, but green in a reducing atmosphere. The
atmosphere within a kiln can be adjusted to produce complex effects
in glaze.
Kilns may be heated by burning
wood,
coal and
gas, or by
electricity. When used as fuels, coal and wood
can introduce smoke, soot and ash into the kiln which can affect
the appearance of unprotected wares. For this reason wares fired in
wood- or coal-fired kilns are often placed in the kiln in
saggars; lidded ceramic boxes, to protect them.
Modern kilns powered by gas or electricity are cleaner and more
easily controlled than older wood- or coal-fired kilns and often
allow shorter firing times to be used. In a Western adaptation of
traditional Japanese
Raku ware firing,
wares are removed from the kiln while hot and smothered in ashes,
paper or woodchips, which produces a distinctive,
carbonised, appearance. This technique is also
used in Malaysia in creating traditional
labu sayung.
History
Earliest known ceramics are the
Gravettian figurines that date to 29,000 to 25,000 BC
It is believed that the earliest pottery wares were hand-built and
fired in bonfires. Firing times were short but the
peak-temperatures achieved in the fire could be high, perhaps in
the region of 900 degrees Celsius, and were reached very quickly.
Clays tempered with sand, grit, crushed shell or crushed pottery
were often used to make bonfire-fired ceramics, because they
provided an open body texture that allows water and other volatile
components of the clay to escape freely. The coarser particles in
the clay also acted to restrain shrinkage within the bodies of the
wares during cooling, which was carried out slowly to reduce the
risk of thermal stress and cracking. In the main, early
bonfire-fired wares were made with rounded bottoms, to avoid sharp
angles that might be susceptible to cracking. The earliest
intentionally constructed kilns were
pit-kilns or trench-kilns; holes dug in
the ground and covered with fuel. Holes in the ground provided
insulation and resulted in better control over firing.
The
earliest known ceramic objects are Gravettian figurines such as those discovered at
Dolni Vestonice in the modern-day Czech Republic
. The
Venus of Dolní Věstonice
(Věstonická Venuše in Czech) is a Venus figurine, a statuette of a
nude female figure dated to 29,000–25,000 BCE (Gravettian
industry). The earliest pottery ware found to date was excavated
from the
Yuchanyan Cave in southern
China and the
Proceedings of
the National Academy of Sciences in 2009 reports that the
ware dates back to 18,000 years ago. Pottery vessels made by the
Incipient Jōmon people of Japan from around 10,500 BCE have also
been found..The term "
Jōmon" means
"cord-marked" in Japanese. This refers to the markings made on clay
vessels and figures using sticks with cords wrapped around them.
Pottery
which dates back to 10,000 BCE have also been excavated in China. It
appears that pottery was independently developed in North
Africa during the tenth millennium b.p. and in
South America during the seventh
millennium b.p.
The
invention of the potter's wheel in
Mesopotamia sometime between 6,000 and
4,000 BCE (Ubaid
period
) revolutionized pottery production.
Specialized potters were then able to meet the expanding needs of
the world's first cities.
Pottery was in use in ancient India during the Mehrgarh
Period II
(5500 - 4800 BCE) and Merhgarh Period III (4800 - 3500 BCE), known
as the ceramic Neolithic and chalcolithic. Pottery, including items
known as the ed-Dur vessels, originated in regions of the Indus
valley and has been found in a number of sites in the
Indus valley civilization.
In the Mediterranean, during the
Greek
Dark Ages (1100–800 BCE), artists used geometric designs such
as squares, circles and lines to decorate
amphoras and other pottery.
The period between
1500-300 BCE in ancient Korea
is known as
the Mumun Pottery
Period.
The quality of pottery has varied historically, in part dependent
upon the repute in which the potter's
craft was held by the community .
For example, in the
Chalcolithic period in Mesopotamia,
Halafian
pottery
achieved a level of technical competence and sophistication, not
seen until the later developments of Greek
pottery with Corinthian and Attic
ware . The distinctive Red
Samian
ware of the Early
Roman Empire was
copied by regional potters throughout the Empire. The
Dark Age period saw a collapse in the quality of
European pottery which did not recover in status and quality until
the
European Renaissance
.
In archaeology
For
archaeologists,
anthropologists, and
historians the study of pottery can help to provide
an insight into past cultures. Pottery is durable and fragments, at
least, often survive long after artifacts made from less-durable
materials have decayed past recognition. Combined with other
evidence, the study of pottery artifacts is helpful in the
development of theories on the organisation, economic condition and
the cultural development of the societies that produced or acquired
pottery. The study of pottery may also allow inferences to be drawn
about a culture's daily life, religion, social relationships,
attitudes towards neighbours, attitudes to their own world and even
the way the culture understood the universe.
Chronologies based on pottery are often essential for dating
non-literate cultures and are often of help in the dating of
historic cultures as well. Trace element analysis, mostly by
neutron activation, allows the
sources of clay to be accurately identified and the
thermoluminescence test can be used to
provide an estimate of the date of last firing. Examining fired
pottery shards from prehistory, scientists learned that during
high-temperature firing, iron materials in clay record the exact
state of Earth's magnetic field at that exact moment.
Environmental issues in production
Although many of the environmental effects of pottery production
have existed for millennia, some of these have been amplified with
modern technology and scales of production. The principal factors
for consideration fall into two categories: (a] effects on workers
and (b) effects on the general environment. Within the effects on
workers, chief impacts are indoor
air
quality,
sound levels and
possible
over-illumination.
Regarding the general environment, factors of interest are off-site
water pollution,
air pollution and disposal of
hazardous materials.
Historically plumbism,
lead
poisoning, was a significant health concern to those glazing
pottery. This was recognised at least as early as the nineteenth
century, and the first legislation in the United Kingdom to limit
pottery workers’ exposure was introduced in 1899. Whilst the risk
of to those working in ceramics is now much reduced it can still
not be ignored. With respect to
indoor air quality, workers can be
exposed to fine
particulate matter,
carbon monoxide and certain
heavy metals. The greatest health risk is the
potential to develop
silicosis from the
long-term exposure to crystalline
silica.
Proper ventilation can reduce the risks, and the first legislation
in the United Kingdom to govern ventilation was introduced in
1899..
Another, more recent study at Laney College
, Oakland, California
suggests that all these factors can be controlled
in a well designed workshop environment.
The use of energy and pollutants in the production of ceramics is a
growing concern. Electric firing is arguably more environmentally
friendly than combustion firing, although the source of the
electricity varies in environmental impact.
Other usages
Due to
the large number of pottery factories, or colloquially, 'Pot
Banks', the English city of Stoke-on-Trent, one of the first industrial cities of the modern
era where, as early as 1785, two hundred pottery manufacturers
employed 20,000 workers, is often called "The Potteries".
For the same reason
the largest
football club in the city are known as "The Potters".
See also
Notes
- Dennis Krueger, Why On Earth Do They Call It
Throwing?, in Ceramics Today
- No. 359: The Dolni Vestonice Ceramics
- "Chinese pottery may be earliest discovered."
Associated
Press. 2009-06-01
- http://arheologija.ff.uni-lj.si/documenta/pdf29/29chi.pdf
- Barnett & Hoopes 1995:23
- Barnett & Hoopes 1995:211
- Proceedings, American Philosophical
Society (vol. 85, 1942). ISBN 1422372219
- Archaeology of the United Arab Emirates: Proceedings of the
First International Conference on the Archaeology of the U.A.E. By
Daniel T. Potts, Hasan Al Naboodah, Peter Hellyer. Contributor
Daniel T. Potts, Hasan Al Naboodah, Peter Hellyer. Published 2003.
Trident Press Ltd. ISBN 190072488X
- Ahn 2000; Bale 2001; Crawford and Lee 2003
- Health Risks In A Victorian Pottery
- Indoor air quality evaluation for the Butler Building
Ceramics Laboratory, Laney College, Oakland, California, Earth
Metrics Incorporated, Alameda County Schools Insurance Association,
December, 1989
- Patterns of Labour - Work and Social Change in the Pottery
Indsutry. Richard Whipp. Routlidge 1990
-
http://www.stokecityfc.com/page/HistoryIndex/0,,10310,00.html
References
- ASTM Standard C 242-01 Standard Terminology of Ceramic
Whitewares and Related Products
- Ashmore, Wendy & Sharer, Robert J., (2000). Discovering
Our Past: A Brief Introduction to Archaeology Third Edition.
Mountain View, California: Mayfield Publishing Company. ISBN
978-0072978827
- Barnett, William & Hoopes, John (Eds.) (1995). The
Emergence of Pottery. Washington: Smithsonian Institution
Press. ISBN 1-56098-517-8
- Childe, V. G., (1951). Man Makes Himself. London:
Watts & Co.
- P.Rado. An Introduction To The Technology Of Pottery.
2nd edition. Pergamon Press. 1988
- W.Ryan & C.Radford.Whitewares: Production, Testing And
Quality Control. Pergamon Press. 1987
- Hamer, Frank and Janet. (1991). The Potter's Dictionary of
Materials and Techniques, Third Edition. London: A & C
Black Publishers. ISBN 0-8122-3112-0.
- Rice, Prudence M. (1987). Pottery Analysis – A
Sourcebook. Chicago: University of Chicago Press. ISBN
0-226-71118-8.
- [4054]
- Tschegg, C., Hein, I., Ntaflos, Th., 2008. State of the art
multi-analytical geoscientific approach to identify Cypriot
Bichrome Wheelmade Ware reproduction in the Eastern Nile delta
(Egypt). Journal of Archaeological Science 35, 1134-1147.
External links
Top topics
Wikis
Quiz
Facts
Map
Misc
Search
