Transformation of Bisque Firing Clay When a kiln reaches around 660 degrees Fahrenheit, chemically bound water begins to be forced off. The clay is totally dried by the time it reaches 930 degrees Fahrenheit. At this moment, the clay has been transformed into a ceramic substance.
Bisque: unglazed clay that has been fired once at a low temperature. It takes on a light brown color and is used for decorative purposes. The word "bisque" comes from the French word "bisque", which means "in two colors".
Mortar: a mixture of fine sand and water used as a binding agent or filler in concrete, plaster, and mortar. The term comes from the Italian word "mortare", which means "to kill by pouring".
Tack: a small piece of cloth used to hold together pieces of leather before they are glued or nailed down. The term comes from old English meaning "to fasten with nails or spikes".
Bake: to heat slowly in an oven or furnace; also, to burn charcoal or wood so that it becomes hard like clay.
Charcoal is very useful for drawing and painting with because it leaves no residue like other materials do when they are burned. It can be made into bricks or blocks for use in torches or cooking pots.
Wood is the most common fuel used for baking these days. Wood burns hot and clean, leaving only air pollution as its waste product.
BONE DRY: This term refers to clay that is ready to be burnt. The clay has lost all of its moisture. At this stage, clay is quite delicate. CENTERING: The act of centering the clay on the potter's wheel so that molding and shaping may begin. A center pull or bull wheel is used for this purpose. Firing: See below. CAST ON: The first step in making ceramic ware. A thin layer of wet clay is wrapped around a stick or dowel and then dried. When dry, the piece is removed from the stick and may be decorated or shaped any way you like. Next, it can be fired in an oven at a high temperature to make it harden and durable. POTTERY: Any object made from clay or glaze used for cooking food. There are many different types of pots available today. Some are designed specifically for cooking while others are used for serving meals at home. DISHWARE: Items used for serving food at a table for one person. They usually have no holes in them for handles, but instead are designed to be placed directly on the stove or grill. JARS: Also called containers, jars are used to store foods and beverages. They are available in several sizes and shapes. Some have lids which fit tightly, while others have glass or plastic covers that can be folded down to help keep out insects. LANTERNS: These are large containers used for holding oil or wax.
The clay is allowed to cure before being fired in a bisque fire. It is referred to be "bone dry clay" when it is as dry as it can be in the open air. When the clay has dried completely, it is ready to be burned for the first time. The clay is brittle in its bone-dry state and may quickly break if handled carelessly. On the other hand, if left too long without being burned, the clay will become hard and inflexible.
When burning clay, preferably in a kiln, a small amount of water vapor is produced as the clay burns. The amount of water vapor produced depends on the temperature used during firing. At lower temperatures, less water vapor is produced and at higher temperatures more. Water vapor escapes through the cracks that form as the clay dries out during curing and through holes that are intentionally made during the firing process.
Burning clay releases some of the carbon dioxide that it captured when the clay was forming. Carbon dioxide enters the atmosphere. In addition, water vapor and minerals from the clay deposit themselves on other objects. This is why objects made from burnt clay look so different from ordinary dirt or rock; they have a much smoother surface because of the burnishings that occur during processing.
Clay is a valuable material in many industries including making bricks, ceramics, and sculptures. It is also used as an additive to make concrete harder, stronger, and more flexible.