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A saggar (also misspelled as sagger or segger) is a type of
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.
Materials
Commonly used materials are cordierite (up to 1275 °C), mull ...
. It is a ceramic boxlike container used in the firing of
pottery
Pottery is the process and the products of forming vessels and other objects with clay and other ceramic materials, which are fired at high temperatures to give them a hard and durable form. Major types include earthenware, stoneware and por ...
to enclose or protect ware being fired inside a
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 int ...
. Traditionally, saggars were made primarily from
fireclay
Fire clay is a range of refractory clays used in the manufacture of ceramics, especially fire brick. The United States Environmental Protection Agency defines fire clay very generally as a "mineral aggregate composed of hydrous silicates of alumin ...
. Saggars have been used to protect, or safeguard, ware from open flame, smoke, gases and kiln debris: the name may be a contraction of the word ''safeguard''. Their use is widespread, including in
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 ...
,
Korea
Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic o ...
,
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
and the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
. Saggars are still used in the production of ceramics to shield ware from the direct contact of flames and from damage by kiln debris. Modern saggars are made of
alumina ceramic,
cordierite
Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: to . A high-temperatu ...
ceramic,
mullite
Mullite or porcelainite is a rare silicate mineral formed during contact metamorphism of clay minerals. It can form two stoichiometric forms: 3 Al2 O32 SiO2 or 2Al2O3 SiO2. Unusually, mullite has no charge-balancing cations present. As a result, th ...
ceramic
silicon carbide
Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal sin ...
and in special cases from
zirconia
Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant stabi ...
.
Use of Saggars in Ming porcelain
Saggars were used to protect the precious imperial porcelain wares created at
Jingdezhen
Jingdezhen is a prefecture-level city, in northeastern Jiangxi province, with a total population of 1,669,057 (2018), bordering Anhui to the north. It is known as the "Porcelain Capital" because it has been producing Chinese ceramics for at leas ...
from the flames of the kiln, and keep them from fusing to one another. The creation of saggars in the fifteenth and sixteenth centuries occupied a large proportion of space, labor, and material (fuel and clay) at the imperial manufactury, and there were more kilns devoted to creating them than to firing the final product.
Staffordshire potbanks
By far the largest number of UK pottery manufacturers were based in and around
Stoke-on-Trent
Stoke-on-Trent (often abbreviated to Stoke) is a city and Unitary authorities of England, unitary authority area in Staffordshire, England, with an area of . In 2019, the city had an estimated population of 256,375. It is the largest settlement ...
in a region known as
The Potteries
The Staffordshire Potteries is the industrial area encompassing the six towns Burslem, Fenton, Hanley, Longton, Stoke and Tunstall, which is now the city of Stoke-on-Trent in Staffordshire, England. North Staffordshire became a centre of ...
. Their businesses, locally known as
potbank A potbank is a colloquial name for a pottery factory in North Staffordshire used to make bone china, earthenware and sanitaryware.
Etymology
The term potbank has been used for generations; traditionally it is believed to originate in a business s ...
s, fired their wares in distinctive
bottle oven
A bottle oven or bottle kiln is a type of kiln. The word 'bottle' refers to the shape of the structure and not to the kiln's products, which are usually pottery, not glass.
Bottle kilns were typical of the industrial landscape of Stoke-on-Trent ...
s. At the turn of the twentieth century over 4,000 of these were in use, although by 2014 only 47 survive, all of which are no longer in production but are
listed buildings
In the United Kingdom, a listed building or listed structure is one that has been placed on one of the four statutory lists maintained by Historic England in England, Historic Environment Scotland in Scotland, in Wales, and the Northern Irel ...
.
The saggars were used for the biscuit and the
glost firing
Ceramic glaze is an impervious layer or coating of a vitreous substance which has been fused to a pottery body through firing. Glaze can serve to color, decorate or waterproof an item. Glazing renders earthenware vessels suitable for holding ...
. They were expected to last for about 40 firings; each potbank made their own in a saggar making workshop. Saggars were made from fireclay, by a ''saggar maker'' and two assistants: the ''framemaker'' and the ''bottom knocker''. The framemaker beat the clay into a sheet on a metal table using a large mallet, the ''mow'' or ''mawl''. Using a ''frame'' he would cut it to size, sprinkle it with sawdust and wrap it around a wooden block to make the walls. The framemaker was usually an
apprentice
Apprenticeship is a system for training a new generation of practitioners of a trade or profession with on-the-job training and often some accompanying study (classroom work and reading). Apprenticeships can also enable practitioners to gain a ...
in his late teens. The bottom knocker, usually a boy in his early teens, did the same on a smaller scale, constructing the round or banjo-shaped bottom. Again the mow was used to beat the air out of the clay and flatten the sheet. The saggar maker was an experienced craftsman who paid his assistants out of his
piece-work
Piece work (or piecework) is any type of employment in which a worker is paid a fixed piece rate for each unit produced or action performed, regardless of time.
Context
When paying a worker, employers can use various methods and combinations o ...
earnings: he took the bottom and the sides onto a wheel and using his thumbs joined the sides to the bottom.
[ The ''green'' saggars were dried and then placed on the top of bungs during the next firing of the kiln.
The unfired ceramic ware was placed in saggars and then biscuit fired, before being glazed and again placed in saggars prior to being glost fired. Ware may then be decorated, and placed on refractory ''bats'' and fired again such as in a ]muffle kiln
A muffle furnace or muffle oven (sometimes retort furnace in historical usage) is a furnace in which the subject material is isolated from the fuel and all of the products of combustion, including gases and flying ash. After the development of ...
.
A ''saggar maker's bottom knocker'' was a job title considered sufficiently amusing for it to be featured on the television panel show What's My Line?
''What's My Line?'' is a panel game show that originally ran in the United States on the CBS Television Network from 1950 to 1967, originally in black and white and later in color, with subsequent U.S. revivals. The game uses celebrity panelis ...
.[Saggar making]
/ref> Whilst saggar making was a skilled craft, bottom knocking was far less skilled, consisting of beating clay into a metal ring.
Studio pottery use
From the twentieth century studio potters have used saggars to create decorative ceramic pieces. In this use saggars are used to create a localised reducing atmosphere, or concentrate the effects of salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
s, metal oxide
An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...
s and other materials on the surface of their ware.
Some pots may be carefully prepared for saggar firing. One method creates a smooth surface covered with clay slip, terra sigillata
Terra sigillata is a term with at least three distinct meanings: as a description of medieval medicinal earth; in archaeology, as a general term for some of the fine red Ancient Roman pottery with glossy surface slips made in specific areas of t ...
, which responds particularly well to the saggar technique. This slip covering may be burnished to achieve a gloss. Prepared pots are nestled into saggars filled with beds of combustible
A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...
materials, such as sawdust
Sawdust (or wood dust) is a by-product or waste product of woodworking operations such as sawing, sanding, milling, planing, and routing. It is composed of small chippings of wood. These operations can be performed by woodworking machinery, ...
, less combustible organic materials, salts and metals. These materials ignite or fume during firing, leaving the pot buried in layers of fine ash. Ware produced in filled saggars may display dramatic markings, with colours ranging from distinctive black and white markings to flashes of golds, greens and red tones. Porcelain
Porcelain () is a ceramic material made by heating substances, generally including materials such as kaolinite, in a kiln to temperatures between . The strength and translucence of porcelain, relative to other types of pottery, arises mainl ...
and stoneware
Stoneware is a rather broad term for pottery or other ceramics fired at a relatively high temperature. A modern technical definition is a Vitrification#Ceramics, vitreous or semi-vitreous ceramic made primarily from stoneware clay or non-refracto ...
are ideal for displaying the surface patterns obtained through saggar firing. In addition to the use of saggars, some studio potters bundle pots and burnable materials within a heavy wrapping of metal foil.
Saggar clay
Saggar clay, also sagger clayalternative spelling at the Free Dictionary
/ref> (not to be confused with the fine grained "sagger ball clay" which fires to a light cream), is a course grained fire clay
Fire clay is a range of refractory clays used in the manufacture of ceramics, especially fire brick. The United States Environmental Protection Agency defines fire clay very generally as a "mineral aggregate composed of hydrous silicates of alumin ...
which gets its name from the saggars which it is used to make.
References
* Hamer, Frank and Janet. ''The Potter's Dictionary of Materials and Techniques''. A & C Black Publishers, Limited, London, England, Third Edition 1991. .
* Watkins, James C., ''Alternative Kilns & Firing Techniques: Raku * Saggar * Pit * Barrel''
Lark Ceramics Publications, 2007. , .
External links
Potbank Dictionary
Archived for the British Library.
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Pottery