Salt glaze pottery - AbsoluteAstronomy.com

Salt glaze pottery is stoneware

Stoneware

Stoneware is a vitreous or semi-vitreous ceramic ware with a fine texture. Stoneware is made from clay that is then fired in a kiln, whether by an artisan to make homeware, or in an industrial kiln for mass-produced or specialty products...

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

Sodium

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

from the salt reacts with silica in the clay body to form a glassy coating of sodium silicate

Sodium silicate

Sodium silicate is the common name for a compound sodium metasilicate, Na2SiO3, also known as water glass or liquid glass. It is available in aqueous solution and in solid form and is used in cements, passive fire protection, refractories, textile and lumber processing, and automobiles...

. The glaze may be colourless or may be coloured various shades of brown (from iron oxide

Iron oxide

Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...

), blue (from cobalt oxide

Cobalt oxide

Cobalt oxide may refer to*Cobalt oxide - CoO*Cobalt oxide - Co2O3*Cobalt oxide - Co3O4...

), or purple (from manganese oxide

Manganese oxide

Manganese oxide is a generic term used to describe a variety of manganese oxides and hydroxides. It may refer to:* Manganese oxide, MnO* Manganese oxide, Mn3O4* Manganese oxide, Mn2O3* Manganese dioxide, , MnO2...

History

The earliest known production of stoneware was in the Rhineland

Rhineland

Historically, the Rhinelands refers to a loosely-defined region embracing the land on either bank of the River Rhine in central Europe....

of Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

around 1350. Initially, the process was used on earthenware

Earthenware

Earthenware is a common ceramic material, which is used extensively for pottery tableware and decorative objects.-Types of earthenware:Although body formulations vary between countries and even between individual makers, a generic composition is 25% ball clay, 28% kaolin, 32% quartz, and 15%...

. By the 15th century, small pottery towns of the Westerwald

Westerwald

The Westerwald is a low mountain range on the right bank of the River Rhine in the German federal states of Rhineland-Palatinate, Hesse and North Rhine-Westphalia. It is a part of the Rhine Massif...

, including Höhr-Grenzhausen

Höhr-Grenzhausen

Höhr-Grenzhausen is a town in the Westerwaldkreis in Rhineland-Palatinate, Germany. It is a centre for the ceramic industry in the Kannenbäckerland with a professional college for ceramics, another for ceramic form, and many others, hence the nickname Kannenbäckerstadt .Together with the...

, Siegberg, Köln

KOLN

KOLN, digital channel 10, is the CBS affiliate in Lincoln, Nebraska. It operates a satellite station, KGIN, on digital channel 11 in Grand Island. KGIN repeats all KOLN programming, but airs separate commercials...

, and Raeren

Raeren

Raeren is a municipality located in the Belgian province of Liège. It was part of Germany until the First World War, after which it became part of Belgium. It is one of several towns in Eastern Belgium which still predominantly speak German....

in Flanders

Flanders

Flanders is the community of the Flemings but also one of the institutions in Belgium, and a geographical region located in parts of present-day Belgium, France and the Netherlands. "Flanders" can also refer to the northern part of Belgium that contains Brussels, Bruges, Ghent and Antwerp...

, were producing a salt-glazed stoneware. Westerwald Pottery

Westerwald Pottery

Westerwald Pottery or Stoneware is a distinctive type of salt glazed grey pottery from the Höhr-Grenzhausen and Ransbach-Baumbach area of Westerwaldkreis in Rheinland-Pfalz, Germany.It is known as Kannenbäckerland Stoneware...

was characterized by stamped medallions and the use of a cobalt

Cobalt

Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....

oxide based colorant for decoration. Production of salt glaze pottery in Westerwald

Westerwald

The Westerwald is a low mountain range on the right bank of the River Rhine in the German federal states of Rhineland-Palatinate, Hesse and North Rhine-Westphalia. It is a part of the Rhine Massif...

ceased because of environmental considerations in 1983.

In the UK during the 17th century and 18th century high quality salt-glazed stoneware was produced in Derbyshire

Derbyshire

Derbyshire is a county in the East Midlands of England. A substantial portion of the Peak District National Park lies within Derbyshire. The northern part of Derbyshire overlaps with the Pennines, a famous chain of hills and mountains. The county contains within its boundary of approx...

, Nottinghamshire

Nottinghamshire

Nottinghamshire is a county in the East Midlands of England, bordering South Yorkshire to the north-west, Lincolnshire to the east, Leicestershire to the south, and Derbyshire to the west...

, London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

and Staffordshire

Staffordshire

Staffordshire is a landlocked county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. Part of the National Forest lies within its borders...

. Salt glazed pottery was also popular in North America from the early 17th century until the early 19th century, indeed it was the dominant domestic pottery there during the 19th century. Whilst its manufacturer in America increased from the earliest dated production, the 1720s in Yorktown

Yorktown, Virginia

Yorktown is a census-designated place in York County, Virginia, United States. The population was 220 in the 2000 census. It is the county seat of York County, one of the eight original shires formed in colonial Virginia in 1634....

, significant amounts were always imported from Britain.

The earliest known production of salt glaze pottery in Australia has been dated to 1850-1883.

During the 20th century the technique was promoted for studio pottery

Studio pottery

Studio pottery is made by modern artists working alone or in small groups, producing unique items of pottery in small quantities, typically with all stages of manufacture carried out by one individual. Much studio pottery is tableware or cookware but an increasing number of studio potters produce...

use by Bernard Leach

Bernard Leach

Bernard Howell Leach, CBE, CH , was a British studio potter and art teacher. He is regarded as the "Father of British studio pottery"-Biography:...

. In the 1950s it was introduced into Japanese craft pottery through Leach's association with Shoji Hamada

Shoji Hamada

was a Japanese potter. He was a significant influence on studio pottery of the twentieth century, and a major figure of the mingei folk-art movement, establishing the town of Mashiko as a world-renowned pottery centre.- Biography :...

. Don Reitz introduced salt glazing into the curriculum at Alfred University

Alfred University

Alfred University is a small, comprehensive university in the Village of Alfred in Western New York, USA, an hour and a half south of Rochester and two hours southeast of Buffalo. Alfred has an undergraduate population of around 2,000, and approximately 300 graduate students...

, New York in 1959, and it subsequently spread to other American universities with ceramic art programs.

Due to the significant amount of air pollution resulting from the process environmental clean air restrictions led to the demise of widespread use of salt glazing. It was last used on any large scale for the production of salt-glazed sewer-pipes

Sanitary sewer

A sanitary sewer is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal. Sanitary sewers serving industrial areas also carry industrial wastewater...

, and other than limited use by some studio potters the process is obsolete, although there are ports of it still being used for sewer-pipes in India.

English salt glaze stoneware

Experiments in stoneware production began in England during the second part of the 17th century. The earliest evidence has been dated 1650–1700 at the site of a kiln at Woolwich Ferry

Woolwich Ferry

The Woolwich Free Ferry is a boat service across the River Thames, London, UK, which is licensed and financed by London River Services, the maritime arm of Transport for London...

, London. The similarity of the ware to German products of a similar era has led it to be attributed to immigrant’s potters.

A significant English manufacturer of salt glaze pottery was John Dwight in Fulham

Fulham

Fulham is an area of southwest London in the London Borough of Hammersmith and Fulham, SW6 located south west of Charing Cross. It lies on the left bank of the Thames, between Putney and Chelsea. The area is identified in the London Plan as one of 35 major centres in Greater London...

. In a related patent application, which was granted in 1671, he also claimed to have discovered the mystery of transparent earthenware comonly knowne by the name of porcelaine or China and Persian ware .. ‘

By the 1800s Lambeth

Lambeth

Lambeth is a district of south London, England, and part of the London Borough of Lambeth. It is situated southeast of Charing Cross.-Toponymy:...

in London has become a centre for the production of salt glaze stoneware, and most especially after the establishment of Doulton and Watts Pottery, which later became Royal Doulton

Royal Doulton

The Royal Doulton Company is an English company producing tableware and collectables, dating to 1815. Operating originally in London, its reputation grew in The Potteries, where it was a latecomer compared to Spode, Wedgwood and Minton...

. The company was founded in 1815 when John Doulton formed a partnership with the owner, Martha Jones and foreman, John Watts, of an existing pottery in Lambeth. Initially the factory specialised in utilitarian salt glazed stoneware, similar to that produced by the Fulham factories. During the 1830s and 1840s considerable amounts of salt-glazed sewer-pipes

Sanitary sewer

were produced by Doultons following Sir Edwin Chadwick

Edwin Chadwick

Sir Edwin Chadwick KCB was an English social reformer, noted for his work to reform the Poor Laws and improve sanitary conditions and public health...

's advocacy of improved sanitary conditions. Doultons were also one of the earliest manufacturers of electrical insulators, initially using salt glaze stoneware and for the electrical telegraph

Electrical telegraph

An electrical telegraph is a telegraph that uses electrical signals, usually conveyed via telecommunication lines or radio. The electromagnetic telegraph is a device for human-to-human transmission of coded text messages....

systems. Also, from about 1830 the started production of salt glaze stoneware vessels, which were valued for their acid resistance, for the emerging chemical industries. From the 1850s Doulton & Co.'s decorative stoneware, that was produced in association with the nearby Lambeth School of Art

Lambeth School of Art

Lambeth School of Art was founded in 1854 by William Gregory as a night school associated with the St. Mary the Less Church in London.-History:...

, enjoyed significant success at various international exhibitions, including at The Great Exhibition

The Great Exhibition

The Great Exhibition of the Works of Industry of all Nations or The Great Exhibition, sometimes referred to as the Crystal Palace Exhibition in reference to the temporary structure in which it was held, was an international exhibition that took place in Hyde Park, London, from 1 May to 15 October...

in 1851, Philadelphia Exhibition

Centennial Exposition

The Centennial International Exhibition of 1876, the first official World's Fair in the United States, was held in Philadelphia, Pennsylvania, from May 10 to November 10, 1876, to celebrate the 100th anniversary of the signing of the Declaration of Independence in Philadelphia. It was officially...

in 1876, and also at Chicago

World's Columbian Exposition

The World's Columbian Exposition was a World's Fair held in Chicago in 1893 to celebrate the 400th anniversary of Christopher Columbus's arrival in the New World in 1492. Chicago bested New York City; Washington, D.C.; and St...

in 1893. Their salt glaze decorative products became known as 'Doulton Ware'. By 1890 their decorative stoneware were so successful that 350 designers and artists were employed at the Lambeth factory, including the famous George Tinworth

George Tinworth

George Tinworth was an English ceramic artist who worked for the Doulton factory at Lambeth from 1867 until his death.-Life:...

. Doulton’s Lambeth factory closed in 1956, due largely to new clean air regulations that prohibited the production of salt glaze in the urban environment. Production, but not of salt glazing, was transferred to their factory in Burslem

Burslem

The town of Burslem, known as the Mother Town, is one of the six towns that amalgamated to form the current city of Stoke-on-Trent, in the ceremonial county of Staffordshire, in the Midlands of England.-Topography:...

which had been established in 1877.

Several other stoneware potteries also operated in Lambeth between the mid-18th & 19th centuries, including James Stiff

James Stiff

James Stiff was a noted English potter. He was born in 1808, the son of Robert Stiff, a workhousemaster and farmer in Rougham, Suffolk. In 1831 he married Sarah Faulkner Philpott, and Lucy Potter in 1878....

and Sons and Stephen Green's Imperial pottery. The former having started his pottery career at Doulton in 1830, before opening his own factory in 1843.

The only commercial pottery in the UK currently licenced to produce salt glaze pottery is Errington Reay in Northumberland

Northumberland

Northumberland is the northernmost ceremonial county and a unitary district in North East England. For Eurostat purposes Northumberland is a NUTS 3 region and is one of three boroughs or unitary districts that comprise the "Northumberland and Tyne and Wear" NUTS 2 region...

which was founded in 1878.

Process

The salt glaze is formed on the biscuit body by reaction of common salt with the clay body constituents, particularly silica, toward the end of firing. The body should ideally be richer in silica than normal stoneware, and iron impurities can help produce good salt glazes. A reduction atmosphere can be employed as the reduced iron silicates are very powerful fluxes.

The salting mixture of sodium chloride and water are introduced into the kiln when the appropriate temperature is reached, typically around 900 °C

Celsius

Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...

. As the kiln reaches higher temperatures, typically 1100-1200 °C, the sodium chloride vaporizes and reacts with steam to form hydrogen chloride

Hydrogen chloride

The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...

and soda. These react with the silica in the body and other body constituents. A glaze of fairly high alumina content (0.6 molecular parts) and a relatively low silica content (2.6 molecular parts), and in which the main base is soda, is formed. Salt glazes have been improved by the addition of borax

Borax

Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate, is an important boron compound, a mineral, and a salt of boric acid. It is usually a white powder consisting of soft colorless crystals that dissolve easily in water.Borax has a wide variety of uses...

, and sometimes sodium nitrate

Sodium nitrate

Sodium nitrate is the chemical compound with the formula NaNO3. This salt, also known as Chile saltpeter or Peru saltpeter to distinguish it from ordinary saltpeter, potassium nitrate, is a white solid which is very soluble in water...

, to the salting mixture. Colouring oxides can be incorporated in the salting mixture to give decorative effects, such as a kind of aventurine glaze.

Salt fumes in a firing atmosphere react in the following way:

2NaCl + 2H₂O → 2NaOH + 2HCl

2NaOH → Na₂O + H₂O

In soda firings the reaction is a little more direct, not requiring the presence of water vapor:

Na₂CO₃ → Na₂O + CO₂

Both the hydrogen chloride

Hydrogen chloride

and the carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

are gases; they do not react with the sodium oxide

Sodium oxide

Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form. Treatment with water affords sodium hydroxide....

that binds with the silica and other components of the clay body. Hydrogen chloride

Hydrogen chloride

leaving the kiln will form a hydrochloric acid

Hydrochloric acid

Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

vapor on contact with moisture in the air or kiln exhaust gases. Any remaining sodium oxide

Sodium oxide

Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form. Treatment with water affords sodium hydroxide....

will form salt by reacting with hydrochloric acid

Hydrochloric acid

Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

vapour as the gases exit the kiln. The sodium oxide

Sodium oxide

Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form. Treatment with water affords sodium hydroxide....

(Na₂O) reacts with the alumina and silica in the clay body to form a sodium alumino-silicate glaze

Glaze

Glaze or glazing is a thin shiny coating, or the act of applying the coating; it may refer to:In materials or engineering:* Architectural glass, a building material typically used as transparent glazing material in the building envelope...

. The general reaction is shown below, with the values for x and y varying dependent on the amounts of sodium oxide

Sodium oxide

Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form. Treatment with water affords sodium hydroxide....

, alumina and silica composing the glaze

Ceramic glaze

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

Na₂O + SiO₂ + Al₂O₃·(SiO₂)₂ → (Na₂O)_x·Al₂O₃·(SiO₂)_y

Salt can also be used as a decorative element on selected individual pots. Biscuit ware can be soaked in a brine

Brine

Brine is water, saturated or nearly saturated with salt .Brine is used to preserve vegetables, fruit, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses, or for pickling foodstuffs, as a means of preserving them...

solution to create salted patterns. Rope and other textiles can also be soaked in brine and wrapped around biscuit ware. Salt can also be added, in solution, to coloured clay slips and can be sprinkled onto biscuit ware in protective, ceramic containers called saggars

Saggar fired pottery

Saggar firing is a technique for the firing of pottery.Saggars are ceramic, boxlike containers which can be used to enclose or protect ware in kilns. Traditionally saggars were made primarily from fireclay. Saggars have been used to protect, or safeguard, ware from open flame, smoke, gases and kiln...

. A related technique, soda firing, substitutes soda ash

Sodium carbonate

Sodium carbonate , Na2CO3 is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...

and / or sodium bicarbonate

Sodium bicarbonate

Sodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula Na HCO3. Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder. It has a slightly salty, alkaline taste resembling that of washing soda . The natural mineral form is...

for common salt. Whilst the application method is a little different, the alternatives need to be sprayed into the kiln, results are similar to salt glazing but for subtle differences in texture and colour.

External links

Further reading
The Adam Weitsman Collection of American Stoneware in the New York State Museum.
http://www.paulsoldner.com/essays/lowfire.htmlLow-fired-salt-fuming by Paul Soldner
Paul Soldner
Paul Soldner was an American ceramic artist.- Biography :...

]

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

History

English salt glaze stoneware

Process

Further reading

External links