Okay, so today, we're gonna be talking about one of the very first materials we manipulated as a human species and that is clay. You probably played with it since you were a child. And you always wondered, what is it actually made of and why does it have these properties.

So clay is made of aluminum and silicon and oxygen. So those are three elements that are the most abundant elements in the Earth's crust. So, it's obvious that there's gonna be a lot of clay around and to be found. So when early humans were starting to first manipulate materials, clay was a natural material to use.

So what are some of the properties of clay? So if we think about it, the property of clay that we like the most is the fact that it's got plasticity. It can be manipulated. And that depends upon how much water we've added to the system, right? You can take a clay and make it in to a slurry and it will have no cohesion at all or you can make it in to something that has a cohesion and maintains a shape.

Clay has an unusual property and that it is very soft and ductile and can be manipulated. However when you start to heat it up with, say, a fire, and you heat it up to less than maybe 500 C, you can actually dry it. And when you dry clay, then it maintains it's shape, all right?

It's obviously opaque, I can't see through it. So if I'm gonna build a building out of clay, I better have another way to build a window if I'm gonna try to be able to see out of it. If you take clay and you heat it above 1,000 degrees C.

1,000 degrees C would be sort of comparable to the tip of this flame. If I heated this clay sample to that temperature, I would actually call it firing that clay. And at that point it now transforms into a ceramic which is a very different material, we're gonna talk about that later.

So, how does clay work? All right, I've got these aluminums, and I've got silicons, and I've oxygens for the most part. And what happens is the silicons surrounds itself with little oxygen atoms. And the aluminum surrounds itself with oxygen atoms. And these little cages then network together into a two dimensional structure.

So 2D layered material. Now we're talking about layering on the atomic scale, so it's very, very fine. You may be familiar with a layered structure like mica. This is mica, it's a layered material and you could peel off layers of it, right. But we're talking about layered material on a much finer, finer scale.

So you got to get down to the micron scale, but if you get that small then what happens is water can get between the layers, and that allows the clay to become malleable, all right. And these little layers start to slide past each other. How does clay form?

Well, clay forms because you take rocks and you start to weather them. And weak acids in the rocks will actually reduce the silicates in these rocks down into these very, very fine particles. Now, what's unique about clay is it's defined by its size. So, we think about it, a clay is defined by being smaller than two microns.

Two microns, how big is that? A hair is about 50 to 100 microns. So, you're talking about a tenth of a hair, a hundredth of a hair, in thickness. All right, now if the particle gets that small, what happens is, it doesn't tend to settle when you put it into water.

So, it stays, the water stays, inside the system and does not settle out. If you get something larger, say, and it actually settles out, we call that silt. And then you get into larger and larger particles. All right, so clays can be washed down from the sight of their formation or they can be found where they're actually formed.

So if they're found where they're formed we call them primary clays and if they're washed down we call them secondary clays, all right? And they have many different types depending upon the minerals that are added or a part of the clay. So, and lots of the clays formed during and after the glaciation period.

So the ice age has contributed to the formation of clay in the Earth's crust. All right, so when did we first start to use clay? Well, you can go back to very, very long times ago when we probably were manipulating clay, millions of years ago. But the oldest samples of clay, where we've actually found figurines manipulated in the fire were about 26,000 years ago in Central Europe.

And the interesting thing about these figurines is that they were actually all broken. So we don't know why they were broken. Maybe it was part of a performance art, or religious ritual, or whatever it was, but all these clay figurines were smashed. Now, somewhere around 15,000 years ago, the Japanese actually in the Mesolithic period started to make pottery.

Now these were still hunter-gathers, but they would make pots to cook their food in. So they would have to lug these pots around while they migrated around from site to site looking for food. Around 10, 000 years ago, the Natufians who were living in Jericho, which is in Israel, started to use clay bricks to build buildings.

And so that's one of the earliest forms of buildings that were used out of clay. And again these clay bricks were not fired into a ceramic, they were just dried and heated up. That's a reversible reaction. So, and that happened from 10,000 years ago and then somewhere around 7,000 years ago there was a big civilization called Catal Huyuk which is a society up in Turkey and they used clay for almost 2,000 years.

And they were very entangled with clay, so when you do the reading of the chapter, you'll find out that there's a lot more to understand about how Catal Huyuk depended upon clay as a civilization. Then around 6,000 BC there was the rise of the Mesopotamians and the Sumerians in the Tigris-Euphrates area.

And they used clay quite a bit. And it was the central building material. And then as they became more civilized they actually started to develop new ways of manipulating clay. For example, around 5000BC to 4000BC the potter's wheel was invented. Before that you had to take clay and roll it out, right, and then spin it around to make a pot, right?

And that's the way you make a pot. But now you can sit and put a clay on a wheel and you can make clay pots much faster that way and much more uniformly. Then somewhere around 4000 BC, Cuneiform clay tablets were formed and that's where you took clay and you started doing print on it, lettering.

And the reason that was essential was because around that time frame, you started to have so much trade that people had to keep track of what they were trading. They needed to know whether or not this amount of material had been traded or who owned what land etc.

And so clay became a way of recording and it was obviously the earliest form of writing that we still have records of. They may have been doing writing on other materials but those materials did not have the durability of clay. Okay, so we've had three different areas in which we we're talking about clay civilizations.

And so on this map you can see where Jericho was formed. And Jericho existed somewhere down in the Israeli area and then you see Catal Huyuk which is up in Turkey. And then all the way over here in this map, you see Sumar, and that's where we had the civilizations, the Tigris, Euphrates area.

So, and this image shows the image of what Jericho looked like in terms of what we found in the ruins of Jericho. And you see these are based on sun-baked bricks. And at that time, 10,000 years ago, they were still primarily hunter-gatherers, and so they had not actually gotten to the point where they started to manipulate and develop crops that they could plant.

However, the clay actually helped a lot in that direction. So what happened was is that in that time frame, the would go out and they had a lot of antelope and they could eat those but they also started to harvest wild wheat. Now, wild wheat had an interesting characteristic.

They would go and they would go up to the wheat and they would shake it and the wheat seeds would fall out and the kernels, and they would collect it. What they learned was they were losing an awful lot of wheat to the ground. So then they started harvesting wheat by taking a scythe, they would take clay and would make a scythe out of it.

And they would cut the wheat down and take that wheat back with them. Now what happened there however was is that when they were bringing the wheat stocks back, all the seeds would fall off. And so the wild wheat was not ideal for planting. However, the way that they did get back, some of the seeds did stay on.

So they planted those seeds and then developed what we now know as a modern wheat variety, where the seeds stay on the stock during the harvesting process. So the clay instrument of a scythe actually was important. And here's an image of a scythe from 3000 BC. So when we talk about cuneiform and the ability to store information, they actually did this by using a little wedge of wood to describe letters.

And the oldest actually written story we've ever discovered is, of course, the Epic of Gilgamesh, which is a very long story about this ancient king that lived about 2700 BC. It was discovered in 1853 on 12 different tablets, and it accounts for the adventures of this king who had lived in ancient Mesopotamia.

In terms of the ancient uses of clay, they were primarily used as a building material. However, also, as I mentioned, could be used as a writing material, used as a cooking material, used as a storage material. So you would store food inside clay pots for later use. It was actually used in sling ammunition.

So if I wanna take a piece of clay and I want to make into a ball right and then use a sling shot then I had the ability now to have ammunition. So clay can be manipulated that way. It was actually even manipulated in musical instruments. So they have a type of a flute called La Carina that was made out of clay.

They also used it for medical applications. So there was something called an Armenian bowl, which was basically an early version of milk of magnesia. And which they used it for upset stomachs. So, in terms of modern uses of clay, clay is used still extensively in pottery and building materials, but it's also used as an odor absorbent.

So it turns out clay is very good at absorbing moisture and odors at the same time. Certain types of clay actually swell upon exposure to water, and that clays are used in oil drilling wells. They're also used in gas production. So when you want to use a clay based catalyst to help in the manufacturing of gasoline.

They're used in paper making, so if you have a very white piece of paper, then you're using, it's covered with a kaolinite clay which is very white. And it's used in cement production, chemical filtering, molds and binders. It's even used primarily in land fills and dams. So if you build a dam, use clay in the core of the dam.

And what happens is, if there's ever a break in the dam, when the water gets in there the clay swells. And it plugs up the hole in the dam. Now we're gonna talk more about what you can do with clay when we talk about ceramics, which is basically a fired version of clay.

But at this point we're still restricting our discussion to basically the unfired form of it. Now from a corrosion stand point, clay doesn't corrode. And the reason it doesn't corrode is because clay is already in an oxidized form. So as we go through this class, we're gonna be talking about corrosion and other materials as well.

And those materials that corrode are materials which were probably started as an oxide. And we reduce them back to a metallic form or some form like that. And then it wants to return to its natural state, back with oxygen. But clay has the advantage of already being in the oxidized state.

So examples of different kinds of clays that formed after glaciation would be kaolinite and montmorillonite. So kaolinite is basically something that's one part aluminum, two parts silicon dioxide, and then the rest water. It's also called China Clay, and it has a unique property. And that is, it doesn't tend to have much swelling or shrinking as you heat it up and cool it back down again.

And this is very advantageous for certain things that you might want to do with it. So, this low expansion during this process is really critical for its use. So, if you take Kaolinite and you heat it below 550 degrees C, then all it does is it reversibly dries.

However, if you heat it up above 1000 degrees C then it will actually form a bond that becomes a ceramic and that becomes known as stoneware or porcelain. So your porcelain was a form of Kalonite. So there are many modern uses for Kalonite. For example it's found in cosmetics, it's found in paint, organic farmers use it to try to prevent infestation with insects on their fruit by spraying Kaolinite on the plants.

It's even used in what's called a quick-clot combat gauze in which they use it in triage injuries in the field. So Kaolinite is a really interesting form of clay. Now, another type of clay is Montmorillonite. Montmorillonite is called a Smectite Clay and it's composed of silicon and oxygen but lots of other elements as well.

So it can have sodium, and calcium, and magnesium, etc. And it has the opposite of Kaolinite. It has a very large shrinking and swelling process that goes on during it's manipulation. And so because of that it can be used in things like oil drilling and dams, as we'll talk about later.

In fact, it's used even in your kitty litter, etc. So, you have two kinds of primary clays. Now, there are lots of other types of clays that are used and manipulated. And so these are just two examples.