Introduction to Ceramics Mrs. Morawa TPHS Ceramics

What is Ceramics? Ceramics is the art and science of making more or less permanent objects from earthy, organic materials when they are subject to heat. The elements > EARTH, WATER, AIR and FIRE are all necessary in making ceramics.

What is Clay? Clay is different than mud… it is “plastic” or has “plasticity” – which is the property that allows clay to change shape without tearing or breaking. It will hold it’s shape. Clay is an aggregation (composed of a mixture or minerals separable by mechanical means) of fine-grained mineral fragments. Usually, it is made up of many different kinds of materials Most of a clay body is made up of silica and alumina (and water)

How is Clay Formed? Clay is a product of the weathering of the earth – due to the grinding of geology (water & wind). Result of Feldspathic rock (in the earth’s crust) weathering and decomposing over millions of years. See this video about how erosion creates different kinds of clay > erosion and clay formation Primary clay (Kaolin), Secondary Clay (Ball Clay), & Clay Body

Main Properties of Clay PLASTICITY - The property of clay that allows it to change shape without tearing or breaking. When formed, it will hold that shape. Numerous factors can make clay more plastic. You can spray it with water. You can store it in a bag with water. You can mix new plastic clay with the old.

Main Properties of Clay SHRINKAGE - The decrease in volume of clay as it dries. Water weight and mass are gone when clay is dry. Shrinking happens in 2 stages – during the drying process and again during firing. Some clays decrease in volume almost 20% during the shrinking process. Every clay body is different.

Stages of Clay Dryness There are terms which describe the various stages clay goes through as it dries. https://www.youtube.com/watch?v=haVK_VkfCDk SLIP – watered down clay, consistency of yogurt – “clay glue” PLASTIC – good, working quality of clay, when it can be shaped without bending or cracking. Good for coils, throwing. LEATHER-HARD – clay that has dried enough to be stiff but still contains some water. Clay can be carved and thrown pots can be trimmed at this stage. Stable – for slab building. Cool to the touch. BONE-DRY – clay that has lost its physical water. VERY FRAGILE! GREENWARE – clay that has been through the drying process and is ready to be fired in the kiln * clay can still be reclaimed BISQUEWARE – clay that has been through the first firing in the kiln. It has not been fired to its mature temperature, but it has been made permanent. It is fragile and pourous – and ready to be glazed.

Firing of Clay BISQUEWARE can be glazed (*after first firing) After piece has been glazed, the piece will be fired a second time – The Glaze Fire This time, the piece will obtain the qualities of the fired glaze. Many times this is a more glassy finish, but not all the time. Ware can NOT be reclaimed after firing (BISQUEWARE OR GLAZEWARE. Clay that has NEVER been fired.

Preparation of Clay WEDGING – the process of kneading clay to make it ready to use. Wedging serves the following purposes: Removes air bubbles Homogenizes clay – so it is the same consistency Aligns the particles.

Firing of Clay FIRING – heating pottery or sculpture in a kiln (or open fire) to bring the clay or glaze to maturity. Firing transforms clay (dried out greenware) into hard ceramic. We will be firing up to about 2200 degrees! KILN – a special oven or furnace that can reach very high temperatures and is used to fire clay. Kilns may be electric, gas, or wood-fired. More about the firing process later…