Ceramic glaze is a waterproof coating or a layer of vitreous substance that has been fused with a ceramic body through combustion. Glaze can function to dye, decorate or waterproof goods. Glazing makes the vessel vessel suitable to hold the liquid, sealing the innate porosity of the unsweetened cork pottery. It also gives a harder surface. Glaze is also used on stoneware and porcelain. In addition to its function, glazes can form a variety of surface finishes, including gloss or matte color or gloss. Glaze can also improve the underlying design or texture of either unmodified or etched, engraved or painted.
Most of the pottery produced in the last few centuries has been coated. Tiles are almost always teary, and the terracotta of modern architecture is very often glazed. Shiny bricks are also common. Domestic sanitary ware is always coated, as many ceramics are used in industry, for example ceramic insulators for overhead power lines.
The most important traditional glaze groups, named after their major ceramic tanning agents, are:
- glaze, glazed and transparent pottery after firing, requiring only about 800 Ã, Â ° C (1.470Ã, Â ° F). Used for about 2,000 years around the Mediterranean, in Europe and China. Includes sancai and Victorian majolica.
- tin-glazing pottery, which coats the ware with opaque white glaze. Known in the Ancient Near East and then important in Islamic pottery, from which he passed on to Europe. Includes faience, maiolica, majolica and Delftware.
- Salt-glazed ware, mostly European stoneware. It uses ordinary salt.
- The glaze ash, important in East Asia, is made only of wood or plant ash, which contains lime and lime.
- The feldspathic glaze of porcelain.
Modern materials technology has created a new vitreous glaze not included in this traditional category.
Video Ceramic glaze
Composition
Glaze should include functional ceramic flux by promoting partial melting in clay bodies and other glaze materials. Flux lowers the high melting point of the silica-forming glass, and sometimes boron trioxide. These glass marks may be included in the glaze material, or can be taken from the clay beneath.
The raw materials of ceramic glazes generally include silica, which will be the main glass trace. Various metal oxides, such as sodium, potassium and calcium, act as fluxes to lower the melting temperature. Alumina, often from clay, tightens molten melt to prevent it from slipping off. Dyes, such as iron oxide, copper carbonate or cobalt carbonate, and sometimes opacities such as lead oxide or zirconium oxide, are used to modify the visual appearance of burned glazes.
Maps Ceramic glaze
Process
Glaze can be applied by drying dry dry mixture on the surface of the clay body or by inserting salt or soda into the furnace at high temperatures to create an atmosphere rich in sodium vapor that interacts with aluminum and silica oxide in the body. shapes and glass deposits, producing what is known as salt glaze pottery. Most commonly, glazes in aqueous suspensions of various mineral powders and metal oxides are applied by dipping the pieces directly into the glaze. Other techniques include pouring glazes on pieces, spraying them into pieces with an airbrush or similar device, or applying them directly with a brush or other tool.
To prevent glossy articles from sticking to the kiln during firing either a small part of the item left without glaze, or supported on small refractory support such as spurs and Spilled kilns are removed and discarded after the shooting. The small sign left by the spurs is sometimes seen in finished goods.
The ornaments applied under the glaze on the pottery are commonly referred to as the underglaze. The bottom layer is applied to the surface of the pottery, which can be raw, "greenware", or "biscuits" -fired (initial firing of several articles before glazing and re-firing). The wet glaze - usually transparent - is applied over the decor. The pigment blends with the glaze, and looks beneath the clear layer of glaze. Examples of underglaze decorations are well-known "blue and white" porcelain produced in England, the Netherlands, China and Japan. Striking blue color is achieved by using cobalt in the form of cobalt oxide or cobalt carbonate, both of which are still commonly used.
The ornaments applied over the glaze layer are referred to as overglaze. The overglaze method involves applying one or more layers or glaze layers on a piece of pottery or by applying a non-glaze substance such as enamel or metal (eg gold leaf) over the glaze.
Glaze colors are low temperature glazes that give a more decorative look, like glass. The first shot is fired, the initial firing is called glost firing , then the overglaze decoration is applied, and it's fired again. Once the piece is fired and out of the kiln, the texture becomes smoother because of the glaze.
History
Historically, ceramic glass has grown somewhat slowly, because the right material is needed to be found, and also the firing technology is able to achieve the necessary temperatures reliably.
Brick glazed back to the Elamite Temple in Chogha Zanbil, dated to the 13th century BC. Iron Pagoda, built in 1049 in Kaifeng, China, of shiny bricks is a famous example in the future.
Leading glass pottery was probably made in China during the Warring States Period (475 - 221 BC), and its production increased during the Han Dynasty. The high temperatures of proto-celadon glazed stoneware were made earlier than earthenware vessels, since the Shang Dynasty (1600 - 1046 BC).
During the period of Kofun Japan, Sue ware is adorned with natural green ash glaze. From 552 to 794 AD, different colored glazes were introduced. Three colored glazes of the Tang Dynasty are often used for a single period, but are gradually removed; the exact color and composition of the glaze has not yet recovered. However, natural ash glazes are commonly used throughout the country.
In the 13th century, floral designs were painted with overglazing red, blue, green, yellow and black. Overglazes are becoming very popular because of the special look they give ceramics.
From the eighth century, the use of glaze ceramics is prevalent in Islamic art and Islamic pottery, usually in the form of intricate pottery. Tin-opacified glazing is one of the earliest new technologies developed by Islamic artisans. The first opaque glaze can be found as a blue-painted device in Basra, around the 8th century. Another important contribution is the development of a pot, which dates from the 9th century Iraq. Other centers for innovative ceramic pottery in the Islamic world include Fustat (from 975 to 1075), Damascus (from 1100 to about 1600) and Tabriz (from 1470 to 1550).
Environmental impact
In 2012, more than 650 ceramic manufacturing companies are reported in the United States. Floor tiles, wall tiles, sanitary equipment, bathroom accessories, kitchen utensils, and tableware are all products that contain potential ceramics available to consumers. Heavy metal is a solid metal used in the glaze to produce a particular color or texture. The glaze component is more likely to be washed into the environment when unrecorded ceramic products are exposed to warm or acidic water. The release of heavy metals occurs when ceramic products are not glazed or damaged. Lead and chromium are the two heavy metals commonly used in ceramic glazes that are closely monitored by government agencies because of their accumulated toxicity and ability.
Metal oxide chemistry
Metals used in ceramic glazes are usually in the form of metal oxides.
Lead (II) oxide
Manufacturers of ceramics mainly use tin (II) oxide (PbO) as a flux for low melting range, wide firing range, low surface tension, high refractive index, and resistance to devitrification. Nitrogen dioxide ( NO
2 ) play a role in the mobilization of lead in the environment. In a polluted environment, nitrogen dioxide reacts with water ( H
2 O ) to generate nitrous acid ( HNO
2 ) and nitric acid ( HNO
3 ).
H
2 O 2 NO
2 -> < span> HNO
2 HNO
3
Lead (II) nitrate ( Pb (NOT
3 )
2 ) is formed when lead (II) oxide (PbO) leaded glaze lead exposure to nitrogen dioxide ( NO
2 ) found in the polluted air.
PbO 2 HNO
3 -> Pb (TIDAK
3 )
2 H < br> 2 O
Produk timbal (II) nitrat siap larut dalam air untuk membentuk ion timbal ( Pb 2
) dan ion nitrat ( NO -
3 ):
Pb (TIDAK
3 ) < br> 2 -> Pb 2
2 NO -
3
When consumed, lead will interfere with normal biochemistry by forming a stable chemical bond with amino acids protein. When lead is converted to a stable oxidation state (Pb 2 ), the tin reacts with the sulfhydryl (-SH) cysteine ​​group. Proteins bound to lead can not be used by biological processes and remain in plant and animal tissue.
Tin exposure is strongly associated with negative kidney effects in animals and humans. Kidney deficiency was observed in Wistar rats after two weeks of swallowing acetate orally.
Chromium (III) oxide
Chromium (III) oxide ( Cr
2 O < span>
3 ) is used as a dye in ceramic glaze. Chromium (III) oxide may undergo reaction with calcium oxide (CaO) and atmospheric oxygen in the temperature reached by the kiln to produce calcium chromate ( CaCrO
4 ). The oxidation reaction converts chromium from oxidation state 3 to 6 oxidation. Chromium (VI) is highly soluble and most rapidly out of all other stable chromium forms.
Cr
2 O
3 2CaO 3 / 2 O
2 -> CaCrO
4
Chromium can enter the water system through industrial discharge. Chromium (VI) can enter the environment directly or the oxidants present in the soil may react with chromium (III) to produce chromium (VI). Plants have reduced the amount of chlorophyll when it grows in the presence of chromium (VI).
Prevention
The oxidation of chromium during the manufacturing process can be reduced by the introduction of compounds that bind calcium. The ceramic industry is reluctant to use tin alternatives because lead glazes provide products with brilliant luster and smooth surfaces. The US Environmental Protection Agency has experimented with double glazes, a barium alternative to lead, but they did not succeed in achieving the same optical effect as leaded glazes.
Gallery
- '' Ceramic glaze ''
See also
Footnote
References
- Hamer, Frank, and Janet. Dictionary of Materials and Potter Techniques. A & amp; C Black Publishers, Limited, London, England, Third Edition 1991. ISBNÃ, 0-8122-3112-0.
Source of the article : Wikipedia
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