Pottery Clay Properties

Series Summary

Ceramics, the craft of forming pottery, is over twelve thousand years old, pottery appearing in the tenth millennium before the Birth of Christ. The potter's wheel was invented between the 6th and 2nd millenniums B.C. in Mesopotamia and completely changed pottery production, allowing pottery to be created much faster and more uniform in shape. Today, in the twenty-first century, pottery is produced on a large scale; however, individual potters can mix their own clay or dig it from the ground and focus more on the art and beauty aspects of creating ceramic pottery. Learn how to make pottery clay from raw materials in this free pottery clay making video series featuring Michael Cottrell professor of sculpture and ceramics. Professor Cottrell will teach you about the properties of various types of clay, what various types of clay are used for in ceramics, and what materials you need to make pottery clay. He will demonstrate how to weigh the raw materials to make pottery clay, how to dry mix and wet mix materials for clay, how to process clay with a pug mill, how to process clay by hand, how to condition pottery clay, how to recycle scrap clay, how to find and use natural clay from the ground, and how to test the properties of natural clay for ceramics suitability.

Video Transcript

"Today we're going to take a look at how to make our own clay body for use in ceramic pottery, but before we do that, we're going to need to understand a little bit more about what the clay actually is and how it works. So what is clay exactly? What makes this clay right here so much different from this soil that comes straight out of the ground? They're both naturally occurring materials, they both originate in the ground, so what makes them so different? Obviously the soil that I pulled out of my flower garden is crumbly, it's full of sticks and dirt and other organic materials. This clay however is slick, the particles stick together, it's really sticky, and most importantly when I mush it, it holds its shape. That property is called plasticity. It's the plasticity of the clay that allows the clay to be formed and shaped, and to hold its shape and we can form it into things like ceramic vessels or sculptures. So what is it about the clay that gives it that plastic property? Clay is made up of decomposed feldspathic rocks, rocks like granite. Now, most mountains are made of granite so over eons of time erosion occurs, rain falls on the mountain, washes small particles down into streams which then get washed into rivers, which then get washed into lakes, and these dense particles settle out and become a sedimentary material on the bottom or a lake bed. That's how clay deposits are formed. In areas of the world where there are older mountains, like the southern Appalachians, for instance, there's a lot of natural clay in the ground there because a lot of that erosion has occurred over eons of time. So, particles of clay are shaped like small, flat platelets similar to flecks of mica. If you look at a clay particle under an electron microscope, it looks like lots of little pieces, flat pieces stacked on top of each other. And if you've ever taken two pieces of glass -- maybe you did this in science class with a slide or something like that -- and put it together with some water in between that surface tension in between those two pieces of glass really makes it difficult to pull that glass apart, but they slide back and forth on top of each other really really easily. So, that's the kind, the same principle that's occurring in the clay between those particles, flat platelet-like particles of clay. The water tension, the surface tension of the water in between those flat particles, allows it to expand and contract, be manipulated, and yet continue to hold its shape."