Why Would a Magnet Be Attracted to Ceramic Tile?
Used for centuries in various applications, no one really knows how long people have fired clay to make tiles, bowls, plates and other implements. But a kiln was dug up in Centamura del Chianti, near Siena, Italy recently that dates to the third century B.C. Along with the kiln, diggers unearthed ceramic fragments, thought to be offerings to the “kiln god” in hopes of blessings for future kiln firings. Does this Spark an idea?
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Ceramic Materials
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Ceramic tiles start out as a combination of clay, sand, dolomite, feldspar and quartz quarried from the earth and mixed with approximately 30 percent water. The natural minerals in the clay, sand or dolomite might contain bits of metal such as iron, nickel or cobalt that react to magnets, making the ceramic tile attractive to a magnet. Creating a ceramic tile starts with using these elements after mixing them in a ball mill to create the “body slip.”
Body Slip
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Because the materials that make ceramic tiles are also used in the glazes applied to ceramic tiles during the last phases of firing, the term “body slip” differentiates the tile from the glaze. After making the body slip, it’s heated in a dryer where the moisture content reduces to approximately 6 percent. At this point in the manufacturing process, the body slip takes on the quality of dust or powder, without losing any of its magnetic properties, if it has magnetism in the first place.
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Bisque
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After reaching the powdered state, the dust goes into a large press. Using a force that ranges from a few hundred pounds per square inch up to 100,000 pounds per square inch, this pressure provides the ceramic tile its strength. The presses create the various shapes of tile, including square, rectangular, oval and more. After pressing, the tile is considered "bisque." After forming, the bisque is dried to remove all water. Drying does not remove any magnetic quality inherent in the materials used to form the bisque.
Glazing
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Before glazing, the bisque tile undergoes baking or firing to harden its surface. After baking, a colorful coating called glaze frosts the tile much like a cake is frosted. Applying glaze to one side only adds the various colors to the tile. Tiles with multiple colors undergo several firings for each glazed color. Glazes are made of the same materials as tiles, but often include additions of cobalt, a highly magnetic material. Tiles are magnetic because of the materials that occur in them naturally, which is why some tiles may be magnetic and others not.
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References
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