What Is Porcelain And How Is It Made
Porcelain, whose origin can be traced back to China, can be described as a ceramic material formed by heating various materials together. These materials, including Kaolin which is heated in a kiln to high range temperatures between 1200 and 1400ºC. The strength, translucence, and toughness of porcelain relative to other forms of pottery is a characteristic built into it by the vitrification process, as well as, the formation of the mineral mullite within its body when heated to extremely high temperatures in a kiln. The manufacturing process in porcelain is considered more problematic than other forms of pottery like stoneware and earthenware. It is commonly recognized as the most important pottery type owing to its strength and white color. It has excellent workability and can be modeled into any shape with allowance for decorative indentations and embossments. Because of this characteristic, it is used for making decorative vessels and historical figurines. In addition to its ability to combine brilliantly well with paints and glazes, it has a host of uses in industries.
Types of Porcelain
There are various types of porcelain, some of which include alumina porcelain, vitro porcelain, feldspar porcelain, earthenware, and stoneware.
Alumina porcelain has a similar production method to feldspar porcelain. The major difference is that it is mixed with aluminum which is thought to improve its durability. However, with that increase in durability comes a decrease in translucency.
Its origin can be traced back to America. It has a warmer white tone than feldspar porcelain. It is very durable and a little transparent. In its production process, it is pre-fired at a temperature (800ºC), a little lower than regular porcelain and another firing is done at 1230ºC-1250ºC.
Stoneware, as the name suggests, is a solid material. Yet, it is more porous than normal porcelain. Its base color is usually brown or light grey, depending on what technique was used for its firing. Lately, several variations of this porcelain type have been developed. For example, aluminum can be used in place of the quartz to achieve a stronger and whiter product.
This is a relatively porous porcelain with an opaque glaze. An example of this opaque glaze is tin glaze. The glaze has a high tendency to crack because it is porous. Its strength is weaker than normal porcelain.
Feldspar porcelain has been produced as far back as the 1700s when the Europeans tried to imitate Chinese porcelain. This porcelain type is white with a slightly blue tone than standard porcelain. It is also slightly translucent owing to the high percentage of glass phase in its structure. It is incredibly durable and is fired at a temperature of about 1300-1400ºC.
Constituents of Porcelain
Porcelain is made from a heated mixture of silica, clays, feldspar and flint materials of small particle sizes. These materials are combined in varying proportions – until they attain their fired and unfired properties - to form different types of porcelain. Let’s take a look at these materials one after the other.
Clay: In general, the exact composition of clay would usually depend on where it is extracted. Still, clay would often have closely related properties regardless of where it is gotten. For example, all clays vitrify only at high temperatures. The only exception is when the vitrification threshold has been lowered by the addition of some materials. Also, all clays are refractory. Just as it is with glass, they hold their shape when heated. Porcelain, therefore, combines the low porosity of glass with the ability of clay to retain its shape. Hence, its popularity for domestic usage. Generally, the clay used for making porcelain are ball clay and china clay, and they are composed mostly of hydrous aluminum silicate and kaolinite.
Feldspar: This material is composed mostly of flint and aluminum silicate. Flint is a type of hard quartz used as a flux in a porcelain mixture. Fluxes can be used to reduce the temperature at which liquid glass is formed, usually at about 1000 to 1300ºC. In this liquid phase, the grains used in forming porcelain bond firmly together.
Silica: Silica is a chemical compound formed by a combination of silicon and oxygen gas; two of the most abundant elements on earth. It exists naturally in crystalline, amorphous and impure forms as seen in quartz, opal, and sand respectively. Of all filler types, silica is the most commonly used for firing the porcelain body. Asides facilitating the firing and forming of the body, it also aids to improve the properties of the final product.
In some cases, porcelain might contain low-alkali containing bodies like soapstone or alumina.
Process of Manufacturing Porcelain
Having selected the required raw materials and taking out the required amounts by weight, they are made to undergo a number of preparatory steps. To begin with, they are crushed, then purified. After that, they are mixed together before being subjected to several forming processes. The forming process could be any of pressing, casting, stiff plastic forming or soft plastic forming. The choice of forming process would usually depend on the type of porcelain ware to be produced. After forming the porcelain body, it is then bisque-fired before glazing. Glazing is the process of firing onto a ceramic body a layer of decorative glass. Finally, the porcelain is then fired. Firing involves heating the porcelain body in a type of oven referred to as kiln.
In summary, the manufacturing process of porcelain involves the crushing of materials to be used, cleaning and mixing of such materials, forming process of the body, bisque-firing, glazing, and firing.
Uses of Porcelain
Porcelain is widely used as a form of building material, especially for floor finishes. Basically, there are two types of porcelain tiles used in buildings. They are, namely glazed and thorough-bodied porcelain tiles. Glazed porcelain tiles are tiles with a glaze finish over the top. The glaze is usually added to add color and finish to the tile. These types of tiles are generally used for decorative purposes because of their fine finish and decoration rather than for more practical purposes.
In contrast, thorough-bodied porcelain tiles do not have any form of glaze over their top. They are mostly used for floors, walls, and countertops since they do not have glazes that could be easily eroded from abrasion and constant use.
Porcelain tiles can be used for floors in high-traffic areas such as in malls due to the hardness and toughness of the materials. They are generally non-porous and non-absorbent. Hence, they can be used for floors and surfaces that are regularly exposed to bacteria.
This is one of the most common usages of porcelain. In addition to being thermal shock-resistant, they are also good insulators and are used in areas of high voltages. They are used in the insulation of antennas, as well, as in high-voltage cable terminals. The American Ceramic society even suggests that they are an essential part of electronic components that ensure the proper functioning of telecommunication devices like smartphones and computers.
This might come as a surprise to a few; however, porcelain is also used in medicine. It is used in dentistry for making porcelain jackets otherwise known as caps and crowns. A porcelain jacket is used in dentistry for protecting the surface of a weak or broken tooth. It is usually recommended for rebuilding teeth that have either been ruined by large holes and decay or have previously been broken. In some cases, they are used to help reshape, whiten or align better the existing teeth. It is imperative to note that they are similar to a natural tooth and for this reason are used for anterior teeth.
Despite its use as a utilitarian material, the elegance and beauty of porcelain make it an interesting choice of art material. In ancient times, people discovered that asides being exquisitely beautiful and elegant in design, porcelain objects were also durable. Consequently, porcelain was used for collectibles. In modern times, they are collected as treasures and sold for huge sums.
Ancient treasures like incense burners used in sacrificial ceremonies or tomb figures from burial grounds are now collected as treasures and stored away at museums or sold for huge prices.
Porcelain can also be used for making decorative objects. Some of these objects are used around the home while some others can serve as souvenirs and gift items. Many trinkets and statue exchanged between nations were made from porcelain.
This is one of the earliest uses of porcelain. This ceramic material was used in times for making kitchen wares used for preparing and dishing out food. It was discovered that utensils and dishes made from porcelain were impervious, easy to clean and reuse and were durable when heated. Their use has now gone beyond kitchen wares to the making of other household items like paperweights and penholders.
Because of the durability of porcelain and its electrical resistivity, porcelain is used for making laboratory materials and equipment. For instance, they are used for making wares in a chemical laboratory because of its strength, durability, and ability to resist chemical attack.