materials Properties of Clay
Clay is a type of soil that is pliable when mixed with water, becomes firm when dry, and becomes glasslike when fired at high temperatures. Fired clay is a ceramic material. When glazes are added to the surface it becomes waterproof. The surface of ceramics can range from bright glossy pigments to a flat black color which results from burning the natural clay during the firing process. Clay comes in a variety of natural colors depending on the mineral content of the soil. Plasticity is a material’s ability to be moved around or formed and the strength to hold that form. The plasticity of clay makes it a perfect medium for modeling. When working with clay the sculptor must keep in mind the thickness of the walls. If squeezed too thin the pieces will break off easily, especially with clay that will not be fired such as the air-dry clay you will use in this book. If the clay is too thick, it will crack as the clay shrinks during the drying process. Large masses must be hollowed-out. The water content of the clay is very important during different stages of the process. In its wet state, too much water makes the clay sticky while too little water makes the clay crack and difficult to connect to other pieces. Clay can also crack if it dries too quickly during the drying stage. For this reason the clay sculpture must be covered with a plastic bag to keep it semi-moist, aiding in slowing down the drying process. Once it is completely dry, it can then be fired without risk of exploding in the kiln. These explosions happen when water molecules are still present in the clay. Clays used for pottery are porous, allowing water to escape easily which prevents cracking. Firing clay is best left to those who have been educated on the correct temperatures and times for the specific type of clay being fired in the kiln. Instruction for firing clay will not be addressed in this text. This text introduces air-dry clay. Air-dry clay has acrylic additives that cause it to dry hard without traditional firing.
Tools and Equipment
You can purchase a variety of clay tools that are used to manipulate the clay. Many basic tools of handbuilding can be substituted with items in your home.
a.
b.
c.
d.
(a.) Loop tools are great for trimming or carving clay once it reaches a leather-hard state (defined on page 23). You can form this tool from a piece of sturdy wire, but since wire is round this substitute will not take clay away as cleanly as store bought loops with flat wire.
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