Firing Ceramic Tiles
After the glaze has been applied, it's time to put the tiles in the kiln to be fired. Traditionally, ceramic tile was 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 tile more efficient in the last century. Continuous kilns include tunnel kilns and roller-hearth kilns.
If you've ever been to a sandwich shop where the worker heats the sandwich by giving it a ride through the toaster, then you'll understand these new types of kilns. Rather than sitting in the heat for hours, the tile is rolled through by conveyor belt-type contraptions (the specific apparatus varies from kiln to kiln). The heat inside the kiln is precisely monitored and controlled by computer. In the first half of the tile's journey, things are starting to get warm.
At the center point, maximum temperature, which can be as high as 2,500 degrees Fahrenheit (1,371.1 degrees Celsius), is reached [source: Donegan]. The higher the temperature, the stronger the brick. As the tile makes its way to the opposite side of the tube, it's gradually cooling down. The cooling down period isn't as passive as it might sound, though -- tiles are still changing color. With these rolling, or continuous kilns, the process has gone from hours of stationary baking to less than an hour. That allows the manufacturers to make a lot more tile, at a reasonable price for the marketplace.
The process was also expedited by the resurgence of the monocottura method. Monocottura, an Italian term meaning "fired once," gives ceramic tile a lot more strength. This additional strength is what allowed tile to go from a product best suited for walls to one that is also good for floors [source: Giovannini]. After just one trip through a hot kiln, the tile made with the monocottura method is ready to be sorted and sent off to the store.
If firing a tile just once makes it so much stronger, why bother with any more firings? If you want a tile with many colors or an elaborate pattern, then that tile will be baked with a bicottura method. Though the prefix would indicate that the tile is fired twice, it can actually be fired as many times as necessary. Before each firing, a different colored glaze is applied to the tile, and the process is repeated until the design is complete.
At this point, our superheroic ceramic tile has gone from clay to dust to tile. Ceramic tile may require many more costume changes than Wonder Woman, but it can also go a lot more places in your home than she can.
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