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, Part 2
In the previous post, I described the nature of clay, origins of ceramic practices, and how forming techniques evolved historically. It’s great to be able to shape a useful object out of the mud you pulled from a river bank. But if you can’t fire the piece back into stone, you’ll be drinking gritty tea with that wizard.
Clay Firing Processes
There’s a few fantasy novels around featuring primitive desert tribes that specializes in making and trading fine porcelain pottery. And it always makes me scratch my head. Where are those tribes getting the fuel to fire their clay, if they live in a desert? Firing takes a long time and a lot of fuel, usually wood.
Again, pre-historic peoples fired their pots in the open, simply placing their pots directly into the fire, or above it, if they had a way to suspend it. They probably had plenty of blow ups, too. Clay that is not thoroughly dry may still contain some water. When heated, water turns to steam, which expands and may break or explode the pot. Clay that was not properly formed, may also include air pockets within the walls. Applying heat makes air expand, which can also break or explode the pot.
Eventually, in order to make the most efficient use of their wood fuel, they learned to dig shallow pits to fire their pots, which slowed down the firing process, but ensured more success. That in turn led to building kilns, structures covered with more clay or stones, to trap the heat inside. The longer the pots absorbed heat, the harder the pieces got. Primitive civilizations would not have understood it, but they were getting closer to “vitrification,” the molecular transformation of turning the clay back into stone.
Historically, wood was the primary fuel for firing a kiln, but eventually, some potteries adopted coal and oil as well. Wood firing pottery is still popular in modern ceramics, as it produces unique, natural effects. As the wood is burned, ash travels through the kiln and deposits on the pots, producing a natural “ash glaze.” However, wood firing is a very labor intensive process (another job the pottery apprentice would be responsible for). Cords of wood have to be tossed into the kiln’s firebox at frequent intervals (up to once a minute). Pine is the most common type of wood fuel; hardwoods are usually too expensive and are used only for specialty effects at the end of the firing cycle. Depending on the size of the kiln, a firing may take up to 5 days, with shifts of workers going round the clock. It may take up to another 5 days for the kiln to cool, afterwards, too.
Wood firing kilns can range from very simple structures holding only a few pots, to 100 foot long multi-chambered structures. Ancient Japanese potters contributed significant development to the process of wood firing, through the development of noborigama (“dragon”) kilns, which were built up the sides of hills, to take advantage of the way that heat rises. Western European and American pottery developed the concept of atmospheric glazing, where salt or baking soda was dissolved in water, and sprayed into the kiln (through small ports) during firing. The salt or soda would deposit on the pots, leaving a shiny sealed surface, both decorative (color variations, random designs) and functional (easy to clean, water tight).
The temperature that pottery is fired to, varies according to the type of clay, and the level of vitrification one is trying to achieve. In modern ceramic practices, it’s common to fire stoneware and porcelain to between 2200 and 2400 degrees Fahrenheit. It’s also possible to overfire clay, and cause it to melt into slag. (A big no-no, in communal studios, is to put a low fire clay into a kiln with high fired wares, especially if the instructor doesn’t know. It causes lots of drama, if someone’s error destroys other people’s work!)
Decorations, glazes, color
As mentioned earlier, clay comes in many colors naturally, but they can all be called “earth” tones, in the truest sense of the word. And the firing process only intensifies those colors; whites get whiter, and tan/borwns get darker. Wood firing, even with ash, salt or soda, rarely produces anything other than some shade of an earth tone. As one modern pottery instructor has told me about wood firing, it’s a heck of a lot of work for brown.
Naturally, this got boring, so potters eagerly sought out ways to incorporate more color into their work. Thus came the development of ceramic glazes. Again, technological developments occurred gradually over time, and over geographies. Other media (metal, glass) influenced ceramics, too. Metallic oxides were discovered, purified, and incorporated.
Ceramic glaze is basically a mixture of the raw clay and additional glass forming minerals (silica, in many forms) with small amounts of metallic oxides to provide colors. Again, ancient China, Japan and Korea lead the way, but Persia, Egypt, and later on, Western Europe, also contributed to the development of glaze technology. China developed traditional celadon glazes, an iron based dark green glaze. Chinese porcelain also started to appear (between 1,500 and 1,000 years ago) and was highly prized for its pure white color.
This led the Japanese to develop shino glazes, which were based on feldspathic mixtures. If applied thickly enough, the shino glaze turned white in the firing. (Later on, American pottery developed a range of shino style glazes that rely on ash and atmospheric conditions to develop a range of colors, with a bright orange being highly prized). The Koreans and the Japanese, in competition to some degree, also developed oribe glazes, based on copper oxides. Like the traditional Chinese green celadons, these were intended to mimic green jade. And of course, the Chinese also developed the use of cobalt oxides to paint highly detailed designs on porcelain, which fired to a deep blue color. As trade between Asia and Europe grew, the term “china” came to refer to any fine porcelain ware.
Meanwhile, Europe played catch up with Asia, in the development of ceramic wares. It was expensive to import items from China and Japan, so European potters set about refining the process to produce items at a lower cost. The process of “bisque firing” developed in France in the 1800s. Sometimes called “biscuit firing” the process involved a partial firing. The pots were heated to a temperature range that evaporated out the molecular water, but did not fully vitrify the pots. (Temperature range: 1800 to 1850 Fahrenheit).
In this state, they were highly porous, and easily absorbed the glaze mixtures that were being developed. Glaze, being a slurry of ground silica, clay, and metallic oxides, needed to applied evenly and efficiently. Dipping or pouring glaze slurry onto the porous bisque ware became common.
England and Ireland also developed fine local porcelains during this time. This lead to the rise of well-known brands like Wedgewood and Beleek. Painting on pottery with enamels or other mixtures became common, too. “China painting” is a technique where pigments (still based on assorted metallic oxides) are applied to previously fired (vitrified) wares and then go through a final, lower temperature firing to fuse the pigments onto the piece. Naturally, this looks best on bright white porcelains.
Health effects of working with ceramics
Working in ceramics can have an effect on a person’s health. Pre-industrialized societies who do not understand the particulate or molecular nature of clay, would have little understanding of how it can impact the body. Health effects can be incorporated into fantasy stories for dramatic effect.
Silicosis: In wet form, clay poses few hazards (unless some highly toxic element is mixed into it). However, when dry, clay can generate dust. Trimming debris that lands on the floor can get crushed and release dust. It’s also common to sand dry vessels to smooth out minor surface flaws, which also releases airborne particles. Dust particles can be inhaled, getting permanently lodged in the lungs. The particles are coarse and sharp, causing microscopic scarring of lung tissue. Over time, this leads to silicosis, which can lead to death. There is no treatment for silicosis; only prevention (wear a mask, avoid generating dust). (Yes, lots of modern potters gave themselves a huge pat on the back in the spring of 2020, for already having heavy duty respirators and paper N95 masks on hand).
If you’re pursuing technical accuracy in your fantasy story, describe your studio setting as having a hazy atmosphere, from the dust getting ground up and released into the air by busy workers. If your setting is slightly more enlightened, some people might wear a cloth handkerchief or scarf over their face, to block the dust. While they may not understand what silicosis is, it’s not hard to recognize a pattern of generations of potters dying early deaths from coughing and breathing problems.
Lead poisoning/heavy metal toxicity: Plain clay generally is not toxic by itself, however, many glazes can contain hazardous or toxic chemicals. If your fantasy society is advanced enough to have developed glaze technology, they’re probably using an assortment of metal oxides to produce color in those glazes. Oxidized metal compounds can be ground to fine powders and mixed with glaze bases to produce colors on the fired wares. Iron is by far the most commonly used, as it is relatively plentiful and inexpensive. It comes in a variety of strengths: Yellow ochre is the weakest form of iron oxide, and produces yellow, gold or tan glazes. Red iron oxide (yes, basically, it’s rust), commonly produces rusty reds, but in the right conditions, may also generate dark greens or blues. Cobalt oxide is a very reliable blue colorant. Other metals, including titanium, manganese and chromium are also used. And of course, historically, lead has been used in glazes to brighten the intensity of other colors. No American or European potter has used lead in glazes on functional pottery for a couple generations now – ever since we came to understand just how toxic it is. However, it can sometimes still be found in wares produced in third world countries.
Handling the metal oxides while working with glazes exposed many potters to heavy metal toxicity, leading to all kinds of health problems. Cognitive (brain) issues were the most common. In addition to exposure to the raw powders, either through skin absorption, or inhaled particles into the lungs, toxic fumes can also be generated and inhaled during firing. A famous historical figure in ceramics is George Ohr, the Mad Potter of Biloxi2. He’s revered for making wildly innovative forms at a time when such things were highly uncommon. It’s also theorized he may have suffered from heavy metal toxicity, as a result of his colorful work.
Positive health uses for clay: On the flip side, raw clay has historically been used in medicines and cosmetics. Kaolin, a type of clay that is common in stoneware and porcelain, was and still is an ingredient in, and lends its name to Kaopectate, a common treatment for digestive upsets. Because clay is slightly alkaline, it neutralizes stomach acids, or so the theory goes. There are studio stories of old potters who’d swallow a tiny pinch of raw clay (about the same amount if you were seasoning a plate of food with salt), to calm an upset stomach. If your fantasy includes herbal healing, your healer could mix small amounts of clay with other things. The clay acts as a stabilizer and delivery agent for the other ingredients.
Kaolin clay is also a common base in cosmetics (both historically, and in current use), such as face powder. It provides a stable, non-shiny material that is easy to brush on, and can be colored with vegetable dyes to match skin tones.
Food safety issues
Food safety in pottery goes beyond the presence of lead or other metals in glazes. Wares that have porous surfaces can trap food and bacteria, which can spread illness. One of the reasons glazes were developed, was to create a smooth non-porous surface. In addition to preventing the spread of bacteria, it was easier to clean. However, if the pottery is not properly fired, the glaze may be part of the problem. Glaze defects can include small pin holes, cracks or bare patches (exposed ceramic surface). Glaze shows visible cracks is called “crazed” or “crackled.” Crazed is when the effect is unwanted, and potentially unsafe (inside a cup, for example). Crackled is when the effect is desired for decorative effect (outside of a vase).
Ceramic culture and conflict
While no one can say what kinds of conversations happened in historical studios, there’s plenty of opportunity to infuse modern sensibilities into fantasy stories (pre-industrial cultures or modern fantasy). Modern ceramic culture almost always revolves around participation in group studios, through classes, workshops, and clubs. Ceramics is not the kind hobby that one can become an expert in, by dropping a few hundred dollars and watching some YouTube videos. Equipment is expensive. Skills take practice to develop. Almost all potters learn their skills by starting with a class somewhere. Many high schools, colleges and community arts programs teach beginning level classes. Some universities offer bachelors and masters degrees in ceramics, as well. Working in a group studio environment means that everyone is sharing equipment, kiln space, and ideas. This fosters a strong community. In a fantasy story setting, a pottery studio is a good choice for a large family business, with lots of apprentices.
In modern studios, form fads come and go. Ask any modern potter about French butter keepers, or melting stained glass in a bowl, and you’ll get epic eye rolls.
Teapots are often considered the holy grail object, in pottery studios. It is the most complex form a potter can make, requiring them to make and assemble many components: body, foot, handle, spout, lid, etc. Most potters will attempt a teapot at some point in their career. Just for fun, try an image search on Google or Pinterest for the term “sculptural teapot.”
Conversely, the most common simple objects most potters make are cups, mugs or bowls. To a potter, the only difference between a cup and a mug, is that the mug has a handle on it. But even then, the two terms might be used interchangeably. If your fantasy story features a public market or fair, your character could compare the cups offered by many different potters, as way of evaluating their skills and prices.
If you really want a character to set off a conversational bomb among a group of artisans, have them hold up a cup and ask, “Well, is it art or is it craft?” The “Art versus Craft” debate has been raging in ceramics (and other media, like glass, metal and wood) for 60 to 100 years. Ask 20 different potters, you’ll get 25 different answers. Most of the answers will be variations on “It’s both.” Those who say it’s art, are speaking of the act of creation, of infusing their will and effort into a piece that does more than just hold food or beverage. They seek to have their work inspire the same kinds of emotional responses that traditional two-dimensional wall art does. On the flip side, those who say it’s craft, point to the level of training and skill required to master the techniques. They talk about the complexity of the media, it’s flexibility, and the functionality of the objects created.
Those who say it’s both, recognize that art is created by making choices. Art happens when someone has mastered the techniques, and uses that knowledge to make very specific choices to create a unique expression of their vision. There’s a special kind of magic that happens when a skilled potter applies their knowledge to transform a lump of mud into an elegant, beautiful form. That magic provides opportunity for story-telling in the fantasy world.
Ceramics has unique uses for many common words, as well as some very specialized words. Many were explained above, but here’s a few more you might want to incorporate into your story:
- Wedging: to homogenize the raw clay. There’s several different ways to effectively wedge clay, but the goal is to get the particles loosened up and moving easily, and make sure the water content is equalized. Wedging techniques can include slamming pieces together, or kneading it like bread dough.
- Thixotropic: literally meaning that a substance has a decreased viscosity when stress (force or action) is applied. This is an essential property of clay. Wedging activates the thixotropic nature of clay, making it easier to shape.
- Leather hard: a state of partial dryness in a clay piece. Leatherhard can be somewhat to very stiff, similar to the consistency of cheese. Any attempt to change the shape of the clay will cause it to break. This state is good for surface decorations that include carving or incising, or the attaching small things, like sculptural elements, handles, etc.
- Bone dry: all of the loose water has evaporated out of the clay piece, without actually being fired in a kiln. The piece feels very chalky, and dust can easily be generated by rubbing or scratching the piece gently. The shape of the piece can no longer be changed without breaking it. Some surface decorations and shallow carving may be done in this state. In humid climates, it may be difficult to achieve a truly bone dry state. Potters may place pieces in a warm oven or near their kilns, to help the evaporation process along; although there is risk of loss, if the temperature is too high and the water converts to steam.
- Grog: coarser (than the main clay body) materials added to the clay, to improve working properties. Usually some form of sand, the larger particle sizes adds strength and durability to the clay. Commonly used when making larger vessels, or when using very rapid fire techniques, like raku. The larger particle size can be uncomfortable and harsh on the hands when throwing pots. It also frequently makes clay and finished pieces darker in color.
- Slip: liquid clay. Clay is mixed with so much water that it is becomes liquid, rather than solid. Slip can be mixed to a wide range of consistencies, from peanut butter to milk. Different types of clays can be blended make specialized slips for different effects. For example, a porcelain slip can be painted over a darker stoneware, to get the bright white color on the surface of a less expensive clay body. Slip is also used to help join separate pieces together, acting like a glue.
- Chemicals: the collection of minerals that can be mixed into glazes and slips. Usually in dry powdered form.
- Bat(s): round thin wooden disks affixed to the wheel head. Once a pot is thrown, the bat can be removed from the wheel, to set it aside to dry, without distorting the shape. (In modern ceramic practice, plastic bats are common).
- Trimming: cutting off excess clay from a thrown form, once it has reached a leather hard stage. Also called “turning” in some places, due the similarity with wood turning on a lathe. Pots can be trimmed on the wheel, or off.
- Paper clay: adding lightweight paper fiber to a clay mixture, to give it strength during the forming process. A relatively new technique in modern ceramics. Grades of paper for this ranges from toilet paper to newsprint.
- Adobe: clay bricks used for buildings. Adobe is commonly used by Native American tribes in the American Southwest (Pueblo tribes, some Navajo, Hopi and others). Clay is mixed with straw, and allowed to dry in the sun. The bricks are stacked and formed into houses and buildings. Since they are not fired, they may erode over time due to wind and rain, and need regular maintenance. If used in modern structures, outside walls may be sealed for protection.
- Raku firing: A specialized Japanese technique for rapid firing. The vessels are heated to a moderate temperature (between 1600 and 1850 degrees Fahrenheit) over a short period of time (one or two hours). The kiln is then opened, and the wares are removed, and placed in a separate vessel with combustible materials (leaves, pine needles, newspaper), which ignite and create smoke. The container is quickly covered, trapping the smoke, which penetrates the wares, leaving random decorative effects. After cooling for an hour or two, the pieces are removed. Because of the rapid process, there is risk of loss due to thermal stress. Thus, most potters use very groggy clay that can tolerate the thermal stress. In modern ceramics, it is common to bisque fire pieces first, before the raku firing, to help ensure success. American and European pottery practices have embraced and expanded on the original techniques, incorporating colorful glazes and special effects from different kinds of combustibles.
- Oxidation firing: Vents in the kiln, and the heat source, allow for oxygen (air) to remain in the kiln during firing. Modern electric kilns fire in oxidation. This allows for very bright colors to be generated from glazes and underglazes.
- Reduction firing: A kiln that burns a fuel (natural gas, propane, wood, oil) can consume all of the oxygen in the kiln, faster than additional oxygen can enter through small ports. Firing in reduction (absence of oxygen) can produce special color effects in glazes. For example, a glaze with copper oxide or copper carbonate in it, may turn cherry red, instead of green.
- Vitrification: a glass-like state of solidity. Sometimes called “maturity”, as in “the teapot was fired to maturity.” Vitrification is important in wares intended for food consumption, but may not matter in other objects.
- Cone: A temperature that clay is fired to. A cone is a measure of the work that the heat does to the clay. Different clays will vitrify at different cone temperatures. In some cases, vitrification can be achieved by holding (called “soaking”) the kiln at a slightly lower temperature for a short period of time, rather than going to a higher temperature, and then immediately allowing it start cooling down. This would be done for the sake of energy efficiency. Chart of common cone temperatures: https://www.pinterest.com/pin/534943261960144493/
- Tea ceremony: A Japanese custom of making and serving tea using hand crafted pottery. There are many variations on the ceremony, from simple to very elaborate. The ceremony is commonly used to affirm friendships and alliances. If the participants are especially interested in pottery, the ceremony may actually include raku firing the teapot and cups to be used immediately.
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