Making Ceramic Tiles
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 tile, 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. 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 [source: American Tile]. That moisture helps 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 [source: American Tile].
After that time in the dryer, the body slip is now essentially powder, or dust. As you may remember from the last page, this entire process is sometimes called dust pressing -- and you're about to learn why. The dust is placed into a large press, powered either with electricity or hydraulics. The press pushes the dust into a set size and shape with a force ranging from a few hundred pounds a square inch to 100,000 pounds per square inch (689,475.7 Newtons per square meter) [source: Bedrosians]. That pressure is what gives the finished project its tensile strength. While we commonly see square or rectangular ceramic tile, presses may have shaped imprints to create ovals, diamonds and other unique shapes as well. The shaped body is called the bisque. After the body is formed, it's dried out to remove all last traces of moisture.
Now it's time for that frosting we mentioned -- the glaze. 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 tile, 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. Find out how the final transformation to ceramic tile occurs on the next page.