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Underglaze is a method of decorating
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 ...
in which painted decoration is applied to the surface before it is covered with a transparent
ceramic glaze 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 ...
and fired in 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 ...
. Because the glaze subsequently covers it, such decoration is completely durable, and it also allows the production of pottery with a surface that has a uniform sheen. Underglaze decoration uses
pigments A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compoun ...
derived from oxides which fuse with the glaze when the piece is fired in a kiln. It is also a cheaper method, as only a single firing is needed, whereas
overglaze decoration Overglaze decoration, overglaze enamelling or on-glaze decoration is a method of decorating pottery, most often porcelain, where the coloured decoration is applied on top of the already fired and glazed surface, and then fixed in a second firing ...
requires a second firing at a lower temperature. Many historical styles, for example Persian
mina'i ware ware is a type of Persian pottery developed in Kashan, Iran, in the decades leading up to the Mongol invasion of Persia in 1219, after which production ceased. It has been described as "probably the most luxurious of all types of ceramic war ...
, Japanese
Imari ware is a Western term for a brightly-coloured style of Japanese export porcelain made in the area of Arita, in the former Hizen Province, northwestern Kyūshū. They were exported to Europe in large quantities, especially between the second half ...
, Chinese
doucai ''Doucai'' () is a technique in painting Chinese porcelain, where parts of the design, and some outlines of the rest, are painted in underglaze blue, and the piece is then glazed and fired. The rest of the design is then added in overglaze enamel ...
and
wucai ''Wucai'' (五彩, "Five colours", "Wuts'ai" in Wade-Giles) is a style of decorating white Chinese porcelain in a limited range of colours. It normally uses underglaze cobalt blue for the design outline and some parts of the images, and overgl ...
, combine the two types of decoration. In such cases the first firing for the body, underglaze decoration and glaze is followed by the second firing after the overglaze enamels have been applied. However, because the main or glost firing is at a higher temperature than used in overglaze decoration, the range of colours available in underglaze is more limited, and was especially so for
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 main ...
in historical times, as the firing temperature required for the porcelain body is especially high. Early porcelain was largely restricted to underglaze blue, and a range of browns and reds. Other colours turned black in a high-temperature firing. Examples of oxides that do not lose their colour during a glost firing are the cobalt blue made famous by Chinese
Ming dynasty The Ming dynasty (), officially the Great Ming, was an imperial dynasty of China, ruling from 1368 to 1644 following the collapse of the Mongol-led Yuan dynasty. The Ming dynasty was the last orthodox dynasty of China ruled by the Han peo ...
blue and white porcelain and the cobalt and turquoise blues, pale purple, sage green, and bole red characteristic of
İznik pottery Iznik pottery, or Iznik ware, named after the town of İznik in western Anatolia where it was made, is a decorated ceramic that was produced from the last quarter of the 15th century until the end of the 17th century. İznik was an established ...
– only some European centres knew how to achieve a good red. The painting styles used are covered at (among other articles):
china painting China painting, or porcelain painting, is the decoration of glazed porcelain objects such as plates, bowls, vases or statues. The body of the object may be hard-paste porcelain, developed in China in the 7th or 8th century, or soft-paste porce ...
,
blue and white pottery "Blue and white pottery" () covers a wide range of white pottery and porcelain decorated under the glaze with a blue pigment, generally cobalt oxide. The decoration is commonly applied by hand, originally by brush painting, but nowadays by s ...
,
tin-glazed pottery Tin-glazed pottery is earthenware covered in lead glaze with added tin oxide which is white, shiny and opaque (see tin-glazing for the chemistry); usually this provides a background for brightly painted decoration. It has been important in Is ...
,
maiolica Maiolica is tin-glazed pottery decorated in colours on a white background. Italian maiolica dating from the Renaissance period is the most renowned. When depicting historical and mythical scenes, these works were known as ''istoriato'' wares ...
,
Egyptian faience Egyptian faience is a sintered- quartz ceramic material from Ancient Egypt. The sintering process "covered he materialwith a true vitreous coating" as the quartz underwent vitrification, creating a bright lustre of various colours "usually ...
,
Delftware Delftware or Delft pottery, also known as Delft Blue ( nl, Delfts blauw) or as delf, is a general term now used for Dutch tin-glazed earthenware, a form of faience. Most of it is blue and white pottery, and the city of Delft in the Netherlands ...
. In modern times a wider range of underglaze colours are available. An archaeological excavation at the Tongguan kiln Site proved that the technology of underglaze colour arose in the Tang and Five Dynasties periods and originated from Tonguan,
Changsha Changsha (; ; ; Changshanese pronunciation: (), Standard Chinese, Standard Mandarin pronunciation: ) is the Capital city, capital and the largest city of Hunan Province of China. Changsha is the 17th most populous city in China with a popul ...
. However cobalt blue was first used in
Persian pottery Persian pottery or Iranian pottery is the pottery made by the artists of Persia (Iran) and its history goes back to early Neolithic Age (7th millennium BCE). Agriculture gave rise to the baking of clay, and the making of utensils by the peopl ...
. The technique has been very widely used for earthenware and
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 main ...
, but much less often on
stoneware Stoneware is a rather broad term for pottery or other ceramics fired at a relatively high temperature. A modern technical definition is a vitreous or semi-vitreous ceramic made primarily from stoneware clay or non-refractory fire clay. Whether vi ...
.


History


Ptolemaic faience

Ancient
Egyptian faience Egyptian faience is a sintered- quartz ceramic material from Ancient Egypt. The sintering process "covered he materialwith a true vitreous coating" as the quartz underwent vitrification, creating a bright lustre of various colours "usually ...
production in the New Kingdom period employed the use of underglaze in works producing green and blue pieces that are distinct from other eras of production. This was achieved by the use of an underglaze that contrasts with the overglaze. This produces the effect of highlighting and lending spectral variance to relief patterns that are embossed into pieces such as tableware such as bowls or jars. Desired blue and green finishes were achieved with the use of copper oxide on their glazing process. Ptolemaic faience has a self-glazing process. In addition to not using successive layers of glaze after the underglaze, Ptolemaic faience also applied a lower kiln temperature. At the firing stage a bake between is applied to achieve a spectrum between turquoise blue and green. Underglaze in Ptolemaic faience was widely used for Ushabti dolls en masse for grave goods in the late Kingdom period.


Chinese porcelain

Through the Yuan and
Ming dynasty The Ming dynasty (), officially the Great Ming, was an imperial dynasty of China, ruling from 1368 to 1644 following the collapse of the Mongol-led Yuan dynasty. The Ming dynasty was the last orthodox dynasty of China ruled by the Han peo ...
,
Imperial porcelain Jingdezhen porcelain () is Chinese porcelain produced in or near Jingdezhen in Jiangxi province in southern China. Jingdezhen may have produced pottery as early as the sixth century CE, though it is named after the reign name of Emperor Zhenzon ...
was produced with red oxide under glazes and more popular cobalt blue. Cobalt blue underglaze porcelain was adopted into the imperial style for both domestic production and
Chinese export porcelain Chinese export porcelain includes a wide range of Chinese porcelain that was made (almost) exclusively for export to Europe and later to North America between the 16th and the 20th century. Whether wares made for non-Western markets are covered b ...
under the Yuan, Ming and Qing dynasties. Until late in the Xuande period the cobalt was imported from Persia; it has specks with high iron and low
manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...
content. This cobalt had a tendency to run when used in a tin glaze, and Persian artisans relied on the experimentation of the Chinese in Jingdezhen porcelain to achieve clear blue designs in their ceramics. Chinese whiteware was prized as an import to Islamic countries that would then trade cobalt for the manufacture of more Chinese porcelain. This was changed to a Chinese form of cobalt that in its ore form had a higher composition of (
Jacobsite Jacobsite is a manganese iron oxide mineral. It is in the spinel group and forms a solid solution series with magnetite. The chemical formula is (Mn,Mg)Fe2O4 or with oxidation states and substitutions: (Mn2+,Fe2+,Mg)(Fe3+,Mn3+)2O4.
) rather than ( Iron(II,III) oxide). Due to the Middle Eastern demand for blue and white porcelain the primary use of this underglaze technology was utilised in creating many designs with Islamic decoration.


Faience

Most styles in this group, such as
Delftware Delftware or Delft pottery, also known as Delft Blue ( nl, Delfts blauw) or as delf, is a general term now used for Dutch tin-glazed earthenware, a form of faience. Most of it is blue and white pottery, and the city of Delft in the Netherlands ...
, mostly used
blue and white pottery "Blue and white pottery" () covers a wide range of white pottery and porcelain decorated under the glaze with a blue pigment, generally cobalt oxide. The decoration is commonly applied by hand, originally by brush painting, but nowadays by s ...
decoration.


Islamic world

Classical
İznik pottery Iznik pottery, or Iznik ware, named after the town of İznik in western Anatolia where it was made, is a decorated ceramic that was produced from the last quarter of the 15th century until the end of the 17th century. İznik was an established ...
from the
Ottoman Empire The Ottoman Empire, * ; is an archaic version. The definite article forms and were synonymous * and el, Оθωμανική Αυτοκρατορία, Othōmanikē Avtokratoria, label=none * info page on book at Martin Luther University) ...
has a stonepaste or frit body, and uses lead glazing rather than tin, and has usually been painted in polychrome.
Persian pottery Persian pottery or Iranian pottery is the pottery made by the artists of Persia (Iran) and its history goes back to early Neolithic Age (7th millennium BCE). Agriculture gave rise to the baking of clay, and the making of utensils by the peopl ...
, which was aware of Chinese styles throughout the period, made great use of underglaze decoration, but mostly in a single colour, often blue using the local cobalt, but also black.


English transfer printed earthenware

Underglaze normally uses a transparent glaze, and therefore reveals the undecorated parts of the fired body. In porcelain these are white, but many of the imitative types, such as
Delftware Delftware or Delft pottery, also known as Delft Blue ( nl, Delfts blauw) or as delf, is a general term now used for Dutch tin-glazed earthenware, a form of faience. Most of it is blue and white pottery, and the city of Delft in the Netherlands ...
, have brownish earthenware bodies, which are given a white tin-glaze and either inglaze or
overglaze decoration Overglaze decoration, overglaze enamelling or on-glaze decoration is a method of decorating pottery, most often porcelain, where the coloured decoration is applied on top of the already fired and glazed surface, and then fixed in a second firing ...
. With the English invention of
creamware Creamware is a cream-coloured refined earthenware with a lead glaze over a pale body, known in France as '' faïence fine'', in the Netherlands as ''Engels porselein'', and in Italy as ''terraglia inglese''.Osborne, 140 It was created about 17 ...
and other white-bodied earthenwares in the 18th century, underglaze decoration became widely used on earthenware as well as porcelain.
Transfer printing Transfer printing is a method of decorating pottery or other materials using an engraved copper or steel plate from which a monochrome print on paper is taken which is then transferred by pressing onto the ceramic piece. Fleming, John & Hugh Ho ...
of underglaze was developed in England in
Staffordshire pottery 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 ce ...
from the 1760s. The patterns were produced in the same way as printed
engraving Engraving is the practice of incising a design onto a hard, usually flat surface by cutting grooves into it with a burin. The result may be a decorated object in itself, as when silver, gold, steel, or glass are engraved, or may provide an in ...
s which were in industrial production at the time. A copper printing plate engraved with the design would transfer underglaze pigment to a piece of dampened tissue paper through a rolled press which could then be adhered to earthenware. The colourants were metallic pigments such as cobalt blue but also include the use of chromium to create greens and browns. To ensure clean transfer, quick firing at a low temperature might be given to fix the colours, known as "hardening on". Initially most production just included one colour, but later techniques were developed for printing in several colours. One type of English
Creamware Creamware is a cream-coloured refined earthenware with a lead glaze over a pale body, known in France as '' faïence fine'', in the Netherlands as ''Engels porselein'', and in Italy as ''terraglia inglese''.Osborne, 140 It was created about 17 ...
using blue, green, orange and yellow colours is known as " Prattware", after the leading manufacturer. This technique was also used in Europe and America in the 19th century on
Creamware Creamware is a cream-coloured refined earthenware with a lead glaze over a pale body, known in France as '' faïence fine'', in the Netherlands as ''Engels porselein'', and in Italy as ''terraglia inglese''.Osborne, 140 It was created about 17 ...
.


Current use

Underglaze is available in a variety of colours from commercial retailers and is used in industrial production of pottery. Low firing temperature underglazes have been formulated as well as application options such as in the form of liquid pens of glaze or solid chalk blocks. The application of underglaze techniques such as stained slips have diversified and a variety of artists have created independent chemical processes of their own to achieve desired effects. Within commercial production there is a decline in underglaze use in comparison to 18th century use due to the creation and improvement of other glazing techniques that do not require such a high heat point. The vibrancy that only underglaze was able to supply is now achievable with a variety of over-glazes therefore discounting the advantage that underglaze commercial production had. A well-known New York underglaze tile and pottery decorator of the 1940s, Carol Janeway (1913-1989), was diagnosed with lead poisoning after eight years of using a lead-based overglaze, retiring in 1950. Her tiles' glazes tested strongly for lead in 2010 using X-Ray Fluorescence technology.


Underglaze transfers

Underglaze transfers are a technique that involves
screenprinting Screen printing is a printing technique where a mesh is used to transfer ink (or dye) onto a substrate, except in areas made impermeable to the ink by a blocking stencil. A blade or squeegee is moved across the screen to fill the open mes ...
or free handing a pattern onto a transfer paper (often
rice paper "Rice paper" has many varieties such as rice paper made from tree bark to make drawing and writing paper or from rice flour and tapioca flour and then mixed with salt and water to produce a thin rice cake and dried to become harder and paper-like ...
or newspaper) which is then placed, dampened, and burnished onto the surface of a
leather-hard In pottery, leather-hard is the condition of a clay or clay body when it has been partially dried to the point where all shrinkage has been completed, and it has a consistency similar to leather of the same thickness as the clay. At this stage, th ...
piece of clay (similar to how a lick-and-stick tattoo might be applied). Artists can acquire rice paper to make their own custom designs, and also purchase pre-printed designs online. Unlike
overglaze Overglaze decoration, overglaze enamelling or on-glaze decoration is a method of decorating pottery, most often porcelain, where the coloured decoration is applied on top of the already fired and glazed surface, and then fixed in a second firing ...
decals, underglaze decals are often applied to greenware and bisque and fired at higher temperatures compared to their
overglaze Overglaze decoration, overglaze enamelling or on-glaze decoration is a method of decorating pottery, most often porcelain, where the coloured decoration is applied on top of the already fired and glazed surface, and then fixed in a second firing ...
counterparts.


Forgeries

The desirability of specific periods of white and blue underglaze Chinese porcelain has led to wide and sophisticated forgery operations. The collector market of blue and white underglaze porcelain is notable due to Orientalism's popularity in Europe. Counterfeiting operations have developed both in foreign areas and within China to profit from the collectability of Ming and Qing dynasty blue and white porcelain. From the baroque period onward, there was a slight decline in the profitability of forging Chinese porcelain as European hard paste techniques were developed but kept as industry secrets in countries such as Germany and France. Despite this there still was and continues to be a high European demand for Chinese blue and White porcelain. In the last three decades there has been a considerable increase in demand for antiques of Ming and Qing porcelain amongst China's rising middle class, which has led to another growth in counterfeiting efforts to supply the large amount of new collectors. This counterfeiting is performed within China and sold to its own population unlike previous rushes in Europe.


Analysis of composition

Due to the extensive efforts to counterfeit Chinese blue and white porcelain, there has been a promotion of detailed scientific analysis of the composition of cobalt used in the underglazes through xeroradiography which has provided insight to the chemical make up of original underglaze recipes on a chemical scale. This in turn reveals historical data about the supply and manufacture industry within China at the time of production of each piece.


Identification of pigment in scientific research

Multiple enquires are being made in an academic and scientific context as to quantifying the physical and chemical composition of multiple types of underglaze. X-ray fluorescence is a primary building block if this but is not acceptable for full understanding. The more prevalent techniques include the use of synchrotron radiation-based techniques. This is to achieve an analysis of the microstructure of underglazes and attempt in verifying and dating historical porcelains such as those of the Ming dynasty. This functions as a method to identify pigments and their origin. Such information is conducive to understanding the trade relations of nations at given times as pigments are sourced internationally and speak to the relationships between nations or empires. Differing cobalts used to colour underglazes in the Middle East and Asia regions were traded and that evidence can be found by inspecting the microstructures of historic samples of pottery using these underglazes therefore supporting other archaeological data on the interactions of these cultures.


Notes


References

* Fournier, Robert, ''Illustrated Dictionary of Practical Pottery'' (Van Nostrand Reinhold, 1973) * Hamer, Frank, and Hamer, Janet, ''The Potter's Dictionary of Materials and Techniques'' (A&C Black/University of Pennsylvania Press, 2004) {{ISBN, 0-8122-3810-9 *Hughes, G Bernard, ''The Country Life Pocket Book of China'', 1965, Country Life Ltd *Savage, George, ''Pottery Through the Ages'', Penguin, 1959


External links


More about underglaze blue printing in the North Staffordshire pottery industry
Glass compositions Glass engineering and science Types of pottery decoration