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Ceramic's tiles

Written by  Author |   Thu, 19 September 2013 12:12

Ceramic tiles are made of natural clay minerals mixed together, glazed on one side, and then fired under extreme heat to create a strong, resilient material.

Historical background
Historically, man wished to create living spaces which were beautiful, durable and user-friendly. With that purpose in mind, ceramic tiles were invented some 4000 years ago. Beautiful tiled surfaces have been found in the oldest pyramids, the ruins of Babylon, and ancient ruins of Greek cities.

Decorative tile work was invented in the near east, where it has enjoyed extended popularity and assumed a greater variety of designs than anywhere in the world. During the Islamic period, all methods of tile decoration were brought to perfection in Persia. In Europe decorated tiles did not come into general use until the second half of the 12th century. The tile mosaics of Spain and Portugal, the maiolica floor tiles of renaissance Italy, the faiences of Antwerp, the development of tile iconography in England and in the Netherlands, and the ceramic tiles of Germany, are all prominent landmarks in the history of ceramic tiles.

Simply defined, ceramic tile is made of clay and in the early days it was made by hand. Later, the only mechanical aid was a wooden mould carved in relief, which indented a pattern on the clay slab. The modern tile industry was advanced by reviving the lost art of encaustic tile-making. The industry was further revolutionized in the 1840s by the ‘dust-pressing' method which consisted of compressing nearly dry clay between two metal dies. Dust-pressing replaced tile-making by hand with wet clay, and facilitated mechanization of the tile-making industry.

Characteristics of ceramic tiles
Ceramic tiles are used almost everywhere -on walls, floors, ceilings, fireplaces, in murals, and as an exterior cladding on buildings. Ceramics are defined as products made from inorganic materials having non-metallic properties. Ceramic tiles have a number of outstanding properties which determine their usefulness. One of the most appreciated is their great durability. This durability can be divided into three types: chemical, mechanical and thermal.

Manufacturing ceramic tiles
As said, ceramic tiles were once made by hand. Wet clay was fashioned into shape, sometimes with the help of a wooden mold, and then left to dry in the sun or fired in a small brick kiln. While a few artisans still craft ceramic tiles by hand, the majority of ceramic tiles made today go through a process known as dry pressing or dust pressing.

Ceramic tile starts life as a lump of earth -- everything in that final product is a natural material. Each manufacturer likely has its own time-tested recipe for ceramic tiles, but clay is usually the main ingredient, along with other items such as sand, feldspar, quartz and water. These ingredients are mixed and grounded up in a ball mill to create what's known as the body slip. A body slip is used to differentiate the body of the tile from its glazed topping; it's the chocolate cake to vanilla frosting. At this point, the body slip contains about 30 percent water. That moisture helps to adhere the ingredients to each other, but as soon as its job is done, it's out of there. To accomplish this, the body slip is put into a dryer and heated; the moisture content is reduced to about 6 percent. After that time in the dryer, the body slip is now essentially powder, or dust. This entire process is sometimes called dust pressing. The dust is placed into a large press, powered either with electricity or hydraulics.

The second step is frosting or glazing. The word comes from the Old English word for glass, which is a good description of glaze. It's that glassy looking substance on one side of the tile. Just as there's a wide variety of delicious frostings, there are many choices for the glaze, including matte and high-gloss, and many ways of applying glaze, from spray to silkscreen. To give the tile some color, pigments are mixed in with the other ingredients. However, even if very vibrant pigments are used, the piece will still look fairly pale, and not like the vibrant tiles we see in the store. That process won't happen until the next step. Though glazing is a typical step for ceramic tiles, it's not essential. Not every tile has to be glazed to be considered ceramic. But there is one qualification that ceramic tiles do have to meet -- they all have to be baked. Before it goes in the kiln, the product has acquired another name: green tile.

After the glaze has been applied, tiles are put in the kiln to be fired. Traditionally, ceramic tiles were left to bake for several hours in what's known as a periodic kiln, such as a beehive kiln. It was the continuous kiln, however, that made the production process of ceramic tiles more efficient in the last century. Continuous kilns include tunnel kilns and roller-hearth kilns. The heat inside the kiln is precisely monitored and controlled by computer.

Digital ceramic printing
Mechanical reproduction processes have been used to increase productivity in ceramic manufacturing since the early days of the Industrial Revolution. Technological improvements relating to both surface design and three-dimensional design were focused primarily on increasing output to reduce the unit costs of making ceramic products. The perennial manufacturing motto, "make more from less", has been applied during every generation involved in making ceramic wares of all kinds, including ceramic tiles. The digital revolution has raised a variety of complex issues for ceramic producers; new digital developments continue to change both the production methods employed and the products created by ceramic manufacturers. These changes are introducing new opportunities for ceramic tiles.

3D ceramics
Digital technology has been widely used in ceramic manufacturing for about three decades, with obvious applications in process control, for example kiln control and firing-cycle management, where the automation of production could lead to more consistent output. A truly digital production process whereby functional three-dimensional ceramic objects could be manufactured quickly, directly from digitized designs, continues to elude the ceramics industry. Perhaps given enough time, nanotechnology will provide the missing process to bridge between computer screen and manufactured three-dimensional ceramic products. Until then, most 3D ceramics including tiles will continue to be volume-produced by more traditional methods.

Two dimensional ceramics
'Two dimensional ceramics' refers essentially to ceramic surfaces, although it is obvious that any ceramic surface must also have a third dimension of 'depth', and an underlying substrate on which to be fired. The process of designing a ceramic surface requires the consideration of many different issues. No ceramic surface can be properly designed in ignorance of the three-dimensional form for which it is the external face. The intended use of the finished ceramic object and the environmental conditions to which it will be exposed are essential factors in the design of its surface. The resources available to the ceramic product's manufacturer, of materials, equipment and production time, must also be considered at the design stage. Surface design for ceramic tiles requires knowledge of the performance characteristics & durability of ceramic materials and an understanding of the most appropriate production methods and technology.

Decorating the tiles
Unglazed tiles: the color range in unglazed tiles is limited to the natural colors of the clay, ranging from light sand to red brick.

Plain glazes: white lead, flint, china stone and china clay were ground to form a glaze. A clear glaze brings out the natural body color and might be applied over any colored decoration. Glazed tiles are decorated with natural and artificially colors. A palette of colors consists of glaze and underglaze colors. The first glazes were blue in color and were made from copper. Also turquoise and light green glaze were popular colors. Ground metal oxides could be added to give different colors.

Encaustic or inlaid: this method was to fill the matrix of a stamped tile with white pipeclay before it was glazed and fired. The two sections fuse during firing.

Mosaic: tiles in such colors as yellow, blue, brown, black, turquoise, green and white were cut and carved into small pieces according to a previously prepared pattern. These pieces are placed close together and liquid plaster poured over them to fill in all the openings and gaps. After the plaster dries and hardens, a large single piece tile panel is created, which is then plastered onto the required wall of the building.

Hand painting: the artist paints freely onto a plain surface tile. The glaze is one centimeter thick, with hand-painted decorations of flowers, plants, geometric designs, birds and human beings. A design could also be copied from an original sketch by 'pouncing'. Alternatively a tile could be transferred, printed and colored by hand.

Carved and modeled tiles: each piece is individually carved in relief or modeled in clay; the pattern could be engraved in outline on the surface of the tile or the design carved in relief or counter-relief on a wood-block which is then pressed into the tile, sometimes painted to emphasize the three-dimensional appearance of the work.

Sgraffito: an early form of decoration, the tile body is covered with coats of slip that is scratched off to produce the design.

Luster painting: the metallic luster of glazed ceramics is a very special type of decoration. It can be red, brown, ochre yellow or green in scattered light and shows, in specular reflection, and colored metallic reflections (blue, yellow, orange, rose.). Metallic copper and silver colloids suspended in glazes compose luster decoration.

Tube lining: A slip is trailed onto the surface of the tile to make raised lines separating the areas where a different color is wanted. Colored glazes are then applied. This technique was used for art nouveau tiles.

Transfer printing: a copper plate is engraved with a design. This would be covered in color with the excess removed leaving the color only in the engraved parts. A tissue paper is pressed onto the plate, and placed color side down onto the tile. When removed, the color is transferred to the tile. This method is quicker, and therefore cheaper than hand painting.

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