What is the process of making ceramic tiles?

Superheroes are defined by their powers and abilities, which they use to battle nefarious villains. From comic books to blockbuster movies, we follow their journeys to see how they effortlessly face evil. What makes a hero captivating is often their origin story — the journey that shapes them into the hero we rely on.

While the idea of a ceramic tile superhero might not be at the forefront of any home improvement enthusiast’s mind, this humble material has its own impressive set of abilities. Ceramic tiles aren't just visually appealing; they are durable and naturally resistant to threats like fire, frost, moisture, and stains. Their rich history is filled with stories of resilience, surpassing even the exploits of superheroes like Batman and Superman. After all, ceramic tiles were used to decorate royal palaces in ancient Europe and churches during the Renaissance in Italy. Despite their understated presence in modern homes, ceramic tiles continue to shine in kitchens and bathrooms worldwide.

So what is the origin story of this humble hero? If Peter Parker gained his powers from a radioactive spider bite and the Green Lantern derives strength from a mystical ring, then what makes ceramic tile the powerhouse it is today? The answer is simple: ceramic tile begins as clay that’s shaped, glazed, and fired. Remarkably, despite its long and storied history, the process has remained largely unchanged. The same ingredients are used, and the method is essentially the same, though it has been modernized and mechanized for faster production.

Ceramic tiles were originally handcrafted. Wet clay was molded into shape, sometimes with the help of a wooden mold, and then either sun-dried or fired in small brick kilns. While some artisans still make tiles by hand, the majority of ceramic tiles today are produced using a technique called dry pressing or dust pressing. This method is more efficient and requires less labor, making ceramic tile more accessible to the masses than it was for Egyptian royalty. On the next page, discover the detailed steps involved in making ceramic tiles, a process that sees our main character take on multiple forms. While it may involve more steps than Superman’s leap over tall buildings, it’s still quite impressive.

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Making Ceramic Tiles

Ceramic tile begins as a lump of earth, with all materials being natural. Each manufacturer likely has its own well-practiced formula, but clay is generally the primary ingredient, along with sand, feldspar, quartz, and water. These ingredients are mixed and ground in a ball mill to create a mixture known as the body slip. The body slip separates the body of the tile from the glaze, much like cake and frosting. At this point, the body slip contains about 30 percent water [source: American Tile]. This moisture helps bind the ingredients, but once it’s done, it’s removed by drying the slip in a dryer, which reduces the moisture content to about 6 percent [source: American Tile].

After the drying process, the body slip essentially turns into powder, or dust. As mentioned earlier, this method is often called dust pressing — and now you’ll see why. The dust is placed into a large press powered either electrically or hydraulically. The press compresses the dust into a specific shape and size using a force ranging from a few hundred pounds per square inch to a maximum of 100,000 pounds per square inch (689,475.7 Newtons per square meter) [source: Bedrosians]. This immense pressure gives the finished product its strength. While most ceramic tiles are square or rectangular, presses can also shape tiles into unique forms like ovals, diamonds, and more. This shaped form is called the bisque, and after forming, it undergoes a final drying to remove any remaining moisture.

Now it’s time for the frosting — the glaze. The term comes from the Old English word for glass, which is an apt description of the glaze. It’s the shiny, glass-like substance that coats one side of the tile. Like frosting, glazes come in a wide range of types, such as matte or high-gloss, and can be applied in several ways, including spraying or silkscreening. To add color to the tile, pigments are mixed with the glaze ingredients. However, even vibrant pigments will give the piece a pale appearance at this stage, and it won’t look as colorful as the tiles we see in stores. That transformation will happen in the next step. While glazing is a common step in ceramic tile production, it’s not a mandatory one. A tile can still be classified as ceramic without glazing.

There is one thing ceramic tiles must have, though: they all have to be baked. Before the tile enters the kiln, it takes on another name: green tile. Read on to learn how the final transformation to a finished ceramic tile happens on the next page.

Firing the Ceramic Tiles

Once the glaze has been applied, the next step is to fire the tiles in the kiln. Historically, ceramic tiles were baked for several hours in what’s called a periodic kiln, such as a beehive kiln. However, the continuous kiln revolutionized ceramic tile production in the last century by making the process far more efficient. Types of continuous kilns include tunnel kilns and roller-hearth kilns.

If you've ever visited a sandwich shop where the worker quickly heats the sandwich by sending it through a toaster, then you’ll be familiar with the mechanics of these modern kilns. Instead of waiting in the heat for hours, the tile is moved through the kiln by conveyor belt systems (the specific design varies from kiln to kiln). The temperature inside the kiln is carefully monitored and regulated by computer. During the first part of its journey, the tile begins to warm up.

At the midpoint of its journey, the tile reaches its maximum temperature, which can soar to as high as 2,500 degrees Fahrenheit (1,371.1 degrees Celsius) [source: Donegan]. The higher the temperature, the stronger the tile becomes. As the tile travels to the end of the kiln, it gradually cools down. However, this cooling period isn’t as passive as it sounds; the tile continues to change color. With rolling or continuous kilns, the firing process has been shortened from hours to less than an hour, enabling manufacturers to produce tiles at a much faster rate and at a more affordable cost for consumers.

The speed of the process was further improved with the return of the monocottura method. Monocottura, an Italian term meaning "fired once," significantly increases the strength of the tile. This added durability is what made ceramic tile suitable not only for walls but also for floors [source: Giovannini]. With just a single trip through the hot kiln, the tile produced using this method is ready to be sorted and sent out for distribution.

But if firing a tile just once makes it so much stronger, why go through multiple firings? The answer lies in the need for intricate designs or multiple colors. In these cases, the tile undergoes the bicottura method. Although the name suggests that the tile is fired twice, it can actually be fired any number of times. Each firing involves applying a different colored glaze to the tile, and the process repeats until the desired design is complete.

At this stage, our heroic ceramic tile has gone from clay to dust to a fully-formed tile. It may require more transformations than Wonder Woman, but it’s also capable of reaching more places in your home than she ever could.