Video: Testing Properties of Natural Clay

Natural clay dug out of the ground should be tested to make sure its properties are right for ceramics. Learn how to test the properties of natural clay to make sure that it is suitable for making pottery in this free pottery making video tutorial.

Video Transcript

So the final and one of the most important steps in using clay, naturally occurring clay is to test it and make sure that it works properly for the techniques that you're going to be using. Specifically, firing techniques. Now, I've got some of the clay that I've cleaned and processed here and I'm just going to make a small test chunk to stick in kiln. Now clay that comes out of the ground tends to be low temperature clay more often than not. So, and you should assume that it is until you have proven, otherwise because low temperature clays will literally melt into a puddle at high temperature cone tin stoneware kinds of temperatures and that can cause a real big mess in your kiln but suffice to say you want to ensure that the clay that you've dug out of the ground is going to be compatible with the firing techniques that you're going to use. So, I'm going to make this test lump and we're going to go and put it in the kiln and fire it and make sure that it works properly. So, I've got my test chunk of this raw clay here. I've let it dry out a little bit and I'm going to put it in this electric kiln here to fire it and test it and make sure that it works right. Now, I'm going to set it on a scrap piece of tile here just an already fired piece of clay just in case it melts or so that I don't mess up the kiln or the kiln shelves if something goes wrong with it. The electric kiln is what we use to do the bisk firing which is the initial firing process that actually converts the clay from clay to a ceramic material. Most people use those words interchangeably but they're actually really different. The clay material can always revert back to a mush substance. Once it's been fired, it actually has a chemical conversion that takes place that chemically-bonded water is driven off and it becomes ceramic which means that it can no longer revert to its original state. If you put it back in water after it's been fired, it just gets wet. Okay, so the kiln has run its course here and I'm going to open it up and check it out and here is our fired chunk. You can see it's been converted to that ceramic material I was talking about and it looks pretty good. It doesn't seem to have any cracking or bloating or other undesirable traits to it. So, we can potentially test this on a little bit larger scale. But it's important that you test this to the highest temperature that you're going to want to use it. Now, we've just done it to a bisk temperature here, but if you're going to use it in a high temperature context in the gas kiln, for instance, where you're going to fire it to a much higher temperature, you need to test it in that way as well to make sure that it's not going to melt too much and turn into a puddle on your kiln shelf.

Testing Properties of Natural Clay

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