This article on making pottery and ceramics is part of the Science in Sci-fi, Fact in Fantasy blog series. Each week, we tackle one of the cultural, historical, or world-building aspects of fantasy with input from an expert. Please join the mailing list to be notified every time new content is posted.
The Expert: Lisa Harnish
Lisa Harnish is a potter, writer and desk jockey. She has lived in Chandler, Arizona, since 1995. When not pushing keys on a keyboard or playing in the mud, she can usually be found sprawled on the living room couch with her dogs, collectively known as the “The Jerky Boys.”
What Writers Should Know About Making Pottery and Ceramics
The difference between “clay” and “ceramic”
In plenty of fantasy novels, it’s common to see the main characters sitting down to talk over a cup of tea, a tankard of ale, or a bowl of stew. Often, the scene is set with a line like: “The wizard poured his hot tea into a clay cup.” As a professional potter, nothing makes me cringe more. There’s a distinct difference between the words “clay” and “ceramic.” Clay is the raw material, extracted from the earth. Clay is decomposed igneous rock. Wind and water have eroded the rock and washed the particles downstream to deposit somewhere. Eventually, some potter comes along, digs up the thick gooey mud, purifies it, and shapes it into a vessel. Then he applies heat until it hardens back into the density of stone. We call this process “firing.” Once fired, the material is technically described as ceramic.
In my example, describing a cup as “clay” implies that it has not yet been fired. If liquid is added, it will eventually cause the vessel to dissolve. Depending on the size of the vessel, and type of clay, this can take minutes or hours. Potters use the verb “slake,” as in, as in: “That cup will slake down, if you put hot tea in it.” Nobody wants to drink gritty tea.
Types of clay, firing temperatures and speed have various effects, but any potter who is making cups for tea, is aiming for vitrification. They’re effectively turning a loose particulate mix back into stone, which is water tight and food safe. In other words, the wizard should drink his tea from a ceramic cup.
The difference between “ceramic” and “pottery”
Another common mistake is referring to all ceramics as pottery. To be precise, “pottery” refers to all functional vessels: cups, plates, bowls, wine jars, teapots, vases, jugs, etc. “Ceramics”, collectively includes pottery, but also means anything made of clay, including non-functional and decorative items, such as masks, signs, wall hangings, dolls, sculpture, beads, bricks, and tiles.
What Is Clay?
At its molecular core, clay is basically alumina, silica, and water. To be precise, the molecular formula is: (Al2O3(SiO2)2(H2O)2) (also expressed as: Al2O7Si2 or H2Al2Si2O8H2O or Al2Si2O5(OH)4 or Al2H4O9Si2). Those molecules, gathered in the thousands, form microscopic particles in the shape of thin, flat platelets. In addition to the molecularly bonded water molecules, the platelet particles are also surrounded by unbonded, loose water, which acts as a lubricant, and gives clay the property of “plasticity,” meaning, the ability to be formed into a shape. Once a form is produced, the clay can be left to dry, where the loose water evaporates out of the clay.
Clay is one of the most common elements in the earth’s crust. It can be found wherever rock erosion has occurred and deposited. Of course, the natural process of erosion means that clay is usually not very pure. Most clay deposits have other elements mixed in, which gives the clay different properties. Raw clay can have a range of colors, including white, pale gray, light tan, rusty red, brown or even black. The darker the clay, the more likely that other elements such as iron, are in the mix. The color of the material usually changes during firing, as well, also depending on the trace elements in the mix.
If you’re looking to situate a clay deposit in your fantasy story, river banks are common sources. If you’re thinking long term (as in, geological ages), dried up, eroded rivers are also a good option. Clay that gets deposited and covered over with other things (at the bottom of the ocean or a large lake), will compress and harden back into stone (over many millions of years). So, deep mines may bore through hard clay deposits. Large scale mining operations can grind down clay to produce good quality materials, too. For more technical information, see: https://ancientpottery.how/where-is-clay-found/
Due to mineral and organic impurities, you’ll need to consider how your fantasy pottery extracts and process its local clay. Digging clay out by hand and hauling it back to the studio is back breaking hard labor. Horses or oxen can help with that. The clay fresh from the side of the river probably has organic matter in it: leaves, sticks, maybe some fish bones. Organic matter in the clay will burn out during firing, but before that, it generates mold growth and lots of stink.
If your fantasy society includes a “master-apprentice” model, it would be the apprentice’s job to process the clay. They would spread it out on rocks or a dry yard, mash it up, and remove any rocks and obvious debris. Depending on what the master potter knows about his local clay, dry clay might even get sieved through screens to purify it. Once as “clean” as the mud can get, it would be mixed with water again, and allowed to age. It takes time for water to fully mix with and surround all of the clay particles, giving it the best plasticity possible. Historically, it was common to age the clay in caves, where the moisture and temperature is constant. Aging might take months, or even years in some cases.
Types of clay
Different kinds of clay can have different properties, when fired. The most common types of finished wares are classified as earthenware, stoneware, and porcelain. There are also some less common subtypes within each, as well. Earthenware has a slight porosity of about 3% to 7%. It will absorb water from its environment, and then gradually release it through evaporation. This makes it a good choice for garden pots (your typical red terra cotta pots found at your local hardware or gardening store). If glazed, earthenware may be sealed over, so that its surface is watertight. Earthenware is commonly used for majolica, which is a style of brightly painted, complex designs used for functional vessels and tiles. It originated on the Mediterranean island of Majorca, and is common throughout the region.
Stoneware has a much lower porosity rating (1 to .5%), and can be glazed or unglazed. It is far more reliable for functional pottery. Porcelain has zero porosity, and is likewise ideal for functional and decorative pottery. Porcelain is further characterized by its purity of color (white) and lack of mineral contaminants in the clay. This makes it an excellent surface for brightly colored decorations created with glaze, enamel or even paint. (And speaking of porcelain, some people seem to think that it’s something other than clay. It’s not. Porcelain is just an exceptionally pure form of clay).
Historical origins of ceramic wares
Almost every culture on Earth has a ceramic tradition of some kind. Pottery sherds (or shards) found in archeological digs have been dated back as far as 25,000 to 30,000 years.
The basic theory is that ancient peoples noticed that the ground under their cooking fires hardened over time, due to the heat. They experimented with forming the raw clay they dug out of the river bank, creating plates and bowls. Then they placed the vessels in or near their fires, to harden. Once cooled, the sturdy form was useful for holding food or water.
The development of ceramic technology paralleled the development of metal working, especially bronze. Metal and ceramic practices both required extracting minerals out of the earth and then figuring out what they could do. Both involve using heat to transform the material into something durable. Whenever one made a leap forward (say, finding a purer deposit of a mineral, or new way to create a form), the other media often adapted that for their own needs.
While almost every civilization on Earth had some level of ceramic development, ancient China and Persia had the largest influence on the development of ceramics, worldwide. Knowledge and techniques spread along trade routes over thousands of years.
You’ve probably all seen the movie clip from Ghost, where Patrick Swayze and Demi Moore cuddle up behind a pottery wheel, smearing mud all over the place (cue the eye rolls). The development of the potter’s wheel is a relatively new invention, in terms of human civilization. Long before the wheel was developed, pottery was shaped and formed by hand.
Coil building is the term for the most common hand building technique. Once the clay was purified, the potter rolls out long ropes of the clay, and then coils it into a circle, building up row upon row, into the desired shape. The inside and outside surface are smoothed, using small pieces of wood, bone or seed pods (these tools are collectively called “ribs”). To help start the form off, the potter may seat the bottom of the piece in another small plate or bowl, just to make it easier to get going.
“Slab construction” or “slab building” refers to using thin sheets of clay to form vessels. The slabs are rolled out with wooden rolling pins, then cut into shapes, and joined together at the edges.
Constructing vessels by hand is time consuming. The need to efficiently produce many pieces drove the development of the pottery wheel. Early examples featured a round disk mounted on an axel, braced in well. A strap or belt was attached and the apprentice pulled it to rotate the wheel head, while the potter shaped the clay. Later on came treadle wheels and kick wheels. A treadle wheel featured a pedal the potter could push, which turned a belt, which turned the wheel head.
A kick wheel (also sometimes called a fly wheel) featured a heavy round wheel at their feet, with the axel post mounted in it, with head on top. The bottom one was kicked or pushed by foot, and directly rotated the top (without belts or straps that would need to be replaced regularly). These are usually made of metal, and require plenty of mineral oil lubricants. Some potters still use kick wheels today, although electric wheels are the most common version now. In modern ceramics, a 1/4 or 1/3 horsepower electric motor is used to pull a belt that rotates the wheel head.
Regardless of how energy is applied to turn the wheel head, once moving, it is by far the most efficient way to form pottery. The potter places a lump of clay on the wheel head and uses the centrifugal force of the spin, along with the force of his hands, to “sink a well” for hollow interior, and then draw the clay upwards (for taller vessels) or outwards (for plates and shallow bowls). A skilled potter can often just toss or throw the lump down and have it well positioned and ready to shape. This is commonly assumed to be the origin of using the verb “to throw” to refer to all stages of shaping raw clay on the wheel (i.e., throwing pots).
As a potter’s skill grows, they can combine elements of pieces thrown on the wheel, into composite forms. For example, a thin tapering form can be attached to the side of a globe, to become the spout of a teapot. A large vase might be made by stacking two or three sections together. Handles are often formed from long coils that are rolled or pulled to the desired length and thickness, and then attached to make pitchers or mugs.
In part 2 of this series, I’ll walk you through the firing processes that turn these raw materials into stone.
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