Where does clay come from?
The ground of course! Clay comes from rocks that have been broken down into tiny particles over time by acts of nature. This process is called weathering. Clay can be found at the subsoil level of the ground which is between bedrock and topsoil. Clay is made up of two main chemicals called Alumina and Silica. Clays come from a variety of rocks and will either be white, gray, tan or red in color. Clay will have a sleek texture to it, but some clays can feel softer or rougher than others.
There are two types of clays found in the ground:
Primary Clay
Primary clay is clay that is found close to where it was formed in nature. Primary clays are often very white and pure in color.
Secondary Clay
Secondary Clay is clay that is found far from where it was formed in nature. As the clay travels by wind and water it often picks up other minerals on its journey. Secondary clays are tan or terracotta colored. Secondary clays tend to be more plastic than primary clays.
Most of the time other ingredients need to be added to natural clays to make them easier to work with. Natural clay with other ingredients added to them is called a clay body.
Here are the three clay bodies that most artist use:
Earthenware Clay Body
Terracotta is the most commonly found clay in nature. It can be easily molded and can be fired in a kiln to become more durable. It can be painted or glazed and made into ceramics but can break or chip easily. Earthenware is a low-fire clay body. Low-fire clays are fired between cones 06-04. Earthenware clay bodies remain porous after firing.
This is the whitest of all natural clays. Its texture is very soft. When fired it becomes very strong and can develop a translucent quality. Porcelain is a high fire clay body. High-fired stoneware is fired between cones 8-11.
Stoneware Clay Body
Stoneware clays are named this because when fired they have the characteristics of stone, which is a hard and dense surface. This is the most used clay body by professional potters that create ceramic pieces because it is so sturdy. Stoneware is a mid to high fire clay body. Mid-fire clays are fired between cones 5-7. High-fired stoneware is fired between cones 8-11. Stoneware clays are refractory, with means they can withstand high temperatures. Stoneware clays are fired to vitrification which means they are not porous after firing and will not absorb water in use.
Book Recommendation
The Magic of Clay by Adalucía Quan ISBN-10 : 159572861
In this picture book guide, budding artists and enthusiasts will learn all about clay, from its chemical makeup and formation to the hands-on processes of molding, throwing, heating, and glazing. Its simple explanations and clear language allow readers to easily understand terminology, techniques, and the art form of ceramics.
Written by: Art Teacher Ruth Post