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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 at a relatively low temperature, often 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 ...
. It is often described as producing "enamelled" decoration. The colours fuse on to the glaze, so the decoration becomes durable. This decorative firing is usually done at a lower temperature which allows for a more varied and vivid palette of colours, using pigments which will not colour correctly at the high temperature necessary to fire the porcelain body. Historically, a relatively narrow range of colours could be achieved with
underglaze Underglaze is a method of decorating pottery in which painted decoration is applied to the surface before it is covered with a transparent ceramic glaze and fired in a kiln. Because the glaze subsequently covers it, such decoration is completely ...
decoration, where the coloured pattern is applied before glazing, notably the
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, pro ...
blue of
blue and white porcelain "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 stenc ...
. Many historical styles, for example
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 wa ...
,
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 ename ...
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 overg ...
, 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. The technique essentially uses powdered glass mixed with coloured pigments, and is the application of
vitreous enamel Vitreous enamel, also called porcelain enamel, is a material made by fusing powdered glass to a substrate by firing, usually between . The powder melts, flows, and then hardens to a smooth, durable vitreous coating. The word comes from the Lati ...
to pottery;
enamelled glass Enamelled glass or painted glass is glass which has been decorated with vitreous enamel (powdered glass, usually mixed with a binder) and then fired to fuse the glasses. It can produce brilliant and long-lasting colours, and be translucent or ...
is very similar but on glass. Both these latter two are essentially painting techniques, and have been since they began. In contrast, on metal painting in enamel arrived very late, long after techniques such as
cloisonné Cloisonné () is an ancient technique for decorating metalwork objects with colored material held in place or separated by metal strips or wire, normally of gold. In recent centuries, vitreous enamel has been used, but inlays of cut gemstones, ...
, where thin wires are applied to form raised barriers, which contain areas of (subsequently applied) enamel, and
champlevé Champlevé is an enamelling technique in the decorative arts, or an object made by that process, in which troughs or cells are carved, etched, die struck, or Casting (metalworking), cast into the surface of a metal object, and filled with vitre ...
, where the metal surface is sunk to form areas where the enamel is poured. In
Chinese porcelain Chinese ceramics show a continuous development since pre-dynastic times and are one of the most significant forms of Chinese art and ceramics globally. The first pottery was made during the Palaeolithic era. Chinese ceramics range from constru ...
, enamels were and are sometimes applied to unglazed pieces; this is called "enamel on the biscuit" and similar terms.


History

Enamel was used in jewellery, applied to metal, from very early on - there are examples in the Tomb of Tutankhamun of c. 1325 BC. Enamel was also used to decorate glass by the time of the Roman Empire. Applied to pottery, it is first seen in 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 wa ...
from the late 12th century, using a group of seven main colours. Presumably the potters learnt the technique from glassmakers. Slightly later it appeared in
Chinese ceramics Chinese ceramics show a continuous development since Chinese Neolithic, pre-dynastic times and are one of the most significant forms of Chinese art and ceramics globally. The first pottery was made during the List of Palaeolithic sites in China, ...
in Cizhou stoneware from as early as the 13th century, with use on porcelain following within a century, though it did not become predominant until later, and the full possibilities were not realized until the 17th and 18th centuries in the famille jaune, noire, rose, verte group of palettes. Some techniques use thin metal leaf, including mina'i ware as well as the more usual pigments, which are typically applied in a liquid or paste form, painted by brush, or using stencils or
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 ...
. The Japanese
kakiemon is a style of Japanese porcelain, with overglaze decoration called "enameled" ceramics. It was originally produced at the factories around Arita, in Japan's Hizen province (today, Saga Prefecture) from the Edo period's mid-17th century onwar ...
style, and other Japanese styles, used the technique from at least the second half of the 17th century. The technique was also developing in Europe, firstly in what the French called ''petit feu'' faience, and in the 18th century in porcelain, and there appears to have been some influence in both directions between Asia and Europe. From about 1770 to the mid 20th century it was the dominant decorative technique in expensive pottery, mostly porcelain, made in Europe, East Asia, and (to a lesser extent) North America. In 18th-century England, where the technique was developed, the earliest forms of
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 ...
on pottery, for example by Sadler & Green in Liverpool, were overglaze, although by the end of the century it was normal to print as underglaze. Today overglaze decoration is much less commonly used, other than in traditionalist wares, as the range of colours available in underglaze has greatly expanded.


Muffle kilns

The kiln used for the second firing is usually called a muffle kiln in Europe; like other types of
muffle furnace 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 ...
s the design isolates the objects from the flames producing the heat (with electricity this is not so important). For historical overglaze enamels the kiln was generally far smaller than that for the main firing, and produced firing temperatures in the approximate range of 750 to 950 °C, depending on the colours used. Typically, wares were fired for between five and twelve hours and then cooled over twelve hours.Hughes, 34-35


Notes


References

*Hughes, G Bernard, ''The Country Life Pocket Book of China'', 1965, Country Life Ltd *
Needham, Joseph Noel Joseph Terence Montgomery Needham (; 9 December 1900 – 24 March 1995) was a British biochemist, historian of science and sinologist known for his scientific research and writing on the history of Chinese science and technology, init ...
(ed), ''Science and Civilisation in China'', Volume 5, Part 12, 2004, Cambridge University Press, , 9780521838337
google books
*Vainker, S.J., ''Chinese Pottery and Porcelain'', 1991, British Museum Press, 9780714114705 *Watson, Oliver, "Pottery under the Mongols" in ''Beyond the Legacy of Genghis Khan'', 2012, BRILL, Ed. Linda Komaroff, , 9789004243408
google books
{{Ceramics-stub Types of pottery decoration