Shrinkage of clay when cooked If you are new to the world of pottery and have fired your first pieces, you may have noticed that the products coming out of the kiln are smaller than they were when you started. So why does clay shrink when fired? There are several reasons why clay shrinks when fired. Firstly, clay loses water. Secondly, it undergoes chemical and physical changes, making it denser than it was originally. This determines how much your artefact will shrink. This shrinking process is often referred to as ‘kiln shrinkage’ or ‘firing shrinkage’ and depends on several factors. Water loss: On average, clay contains 20 per cent water and 9 per cent organic matter. Therefore, a baked piece can weigh almost 30 per cent less than its original weight. Although the clay enters the kiln almost dry, it still contains some water. This water is a combination of residual moisture and chemically bound water. As the clay is baked, residual moisture evaporates and chemically bound water exits the clay . As a result of this drying process, the clay shrinks. Chemical and physical changes: During the kiln process, the organic matter in the clay is burnt, so the clay loses some volume in this process. In addition, the clay goes through a process called vitrification. Vitrification is a process that involves the formation of glass within the clay body. When the raw pottery sherd is fired, glass clay particles begin to form. This liquid glass gradually moves through the particles into the spaces between the particles. As a result, the clay shrinks, because the particles are getting smaller and the spaces between the particles are filling up. Cooking temperature: The higher the firing temperature, the more vitrified the clay becomes. Since vitrification is a process, clay fired at a lower temperature may only be partially vitrified. This means that the clay shrinks less than a fully vitrified piece. Glaze of Shrinking Clay This process of shrinkage of the clay as it is fired is one of the cornerstones of the art of pottery. However, understanding this process allows artists to better utilise the properties of the clay. Understanding factors such as firing temperatures, vitrification degrees and clay mixtures allows the artist to create works closer to the desired result.
Does clay shrink as it dries? The main reason for this situation, which is frequently encountered in pottery art, is that the clay body loses water when it interacts with the surrounding air. As soon as the clay is removed from its plastic packaging, it begins to lose its water content as soon as it comes into contact with the air. If the clay is left in the open, it loses its water to the same level as the surrounding air. This is where shrinkage occurs in the drying process of the clay. clay types with finer particles contain more water. The main reason for this is that as the number of particles in a piece of clay increases, there is more particle surface area to which water can adhere. There is also more water between the particles holding the clay together. Plasticity and the drying speed of the clay are also important. Plastic clay tends to retain this shape when shaped, i.e. it does not tend to loosen or return to its original shape. This property causes the clay to shrink more when it is baked. The fact that organisms increase the elasticity of the clay can also be effective in the drying process of the clay . These organisms burn when baked, which increases the elastic properties of the clay. Plastic clay shrinks more when dried and baked because it has a higher water content. This water is removed when the clay is dried and baked. As a result, the shrinkage of clay during the drying process varies depending on factors such as plasticity, particle structure and water content. Understanding this process is important for producing successful works in clay art. We hope this information will help you better understand the shrinkage of clay during the drying process.