In this clip we're going to take a look at some of the different clays that we use to make ceramics. Even though clay is a naturally occurring material and you could potentially use it directly out of the ground, which we'll talk a little bit more about later, we usually use a combination of these materials blended together, via a recipe, in order to create a clay body with the specific set of properties. Now, sometimes these properties are physical properties in that they give the clay some characteristics working properties that are specifically designed for a particular kind of ceramic work. Raku clay, for instance, is specifically designed to withstand the thermal shock, rapid expansion and contraction that clay bodies might go through when you pull it out of the Raku kiln, red hot kiln into the ambient temperature. Some other kinds of specific properties might be aesthetic. Some clay bodies are kind of a buff color, some are a darker, orangy red color, and some like this porcelain, here, have a distinctive crisp, clean, white kind of color. So all of those things play into what kind of clay we might want to use for a particular purpose. Now, some clays are specifically designed to be used for throwing on the wheel. They stand up very well to the manipulation that occurs when you compress and pull clay body up on the wheel to create large ceramic vessels. Some other kinds of clays are specifically designed for use in hand building, when you're not using a wheel, just creating forms by adding pieces together, using hand building techniques, coils and slabs and things like that. And then another type of clay is called slip. Slip is just a generic term for liquid clay. And some things that you've seen, like slip cast figurines, especially things of that nature, or things that you might have seen at the "paint your own" pottery shops are slip casts. Meaning that a liquid clay has been poured into a plaster mold and the clay has developed a wall thickness on the inside of that mold, the excess is poured out, and thus you have a hollow form. So, those are all different kinds of clays that have specific characteristics for specific techniques. The clay bodies that we use for pottery are, generally, divided up into two categories based on temperature. The temperature at which the clay body matures in the kiln. The temperature at which it's fired to so that it's as dense and as fused as it's going to become. You've probably heard these terms before, there's stoneware and earthenware. The stoneware clays are generally high temperature clays. They're fired to, roughly, cone 10 which is approximately 2,400 degrees Fahrenheit, and earthenware clays, which are lower temperature clays which are fired to approximately 1,985 degrees which is around cone 04, cone 06. Now, the pyrometric cone system is another lecture in and of itself, but, suffice it to say that different types of clays are formulated to mature at different temperatures depending on how you're going to fire them and what their intended use is going to be. For the most part, functional materials, functional pots like mugs and bowls and things like that are generally stoneware clays fired to cone 10, generally in a reduction kiln, which is a gas fired kiln, fired on a natural gas or propane.
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