What Are The Techniques Of Clay Vessels?

Clay vessels are objects made from clay that are fired in a kiln to harden them. They have been an important part of human civilization for thousands of years, with evidence of clay pottery dating back over 20,000 years. Clay’s plasticity when wet and durability when fired have made it a versatile material for creating containers, storage vessels, serving dishes, and decorative artworks across many cultures.

The development of pottery was a major advancement for early human societies. Clay vessels allowed for better food storage and cooking, which improved nutrition and health. They also facilitated trade and the storage of goods. Over time, clay vessel production evolved into an important craft, with potters developing specialized skills and techniques. Distinct ceramic styles emerged in different regions, influenced by local materials and artistic traditions.

Today, clay vessels continue to be popular for their beauty and functionality. From Italian majolica, to Chinese porcelain, to the black pottery of Oaxaca, clay ware reflects tremendous cultural diversity. Pottery also remains important to archaeologists, who study ancient shards to learn about past civilizations. The timeless appeal of these earthy, tactile vessels ensures clay pottery will continue shaping human life into the future.

Collecting Clay

Clay can be collected from many locations, but the type and quality depends on the source. There are three main types of clay used for making ceramic vessels: earthenware, stoneware and porcelain.

Earthenware clay contains lower levels of minerals and melts at lower temperatures. It’s very plastic and easy to work with. Earthenware clay can be dug up from open clay pits, river beds, or shorelines. For example, terracotta clay is an earthenware collected along riverbanks and shorelines in places like Italy.

Stoneware clay contains more minerals, making it denser and more durable when fired at higher temperatures. Deposits of stoneware clay are often found where ancient lakes and seas existed. Stoneware clay can be gathered using tools like picks and shovels from open quarries. An example is the grayish stoneware clay found in central United States.

Porcelain clay has the highest kaolin content, requiring firing at very high temperatures to become translucent and white. Porcelain clay deposits are less abundant than stoneware or earthenware, but can sometimes be found in hillsides and old streams. Care needs to be taken when digging up porcelain clay to keep it free of contaminants.

Preparing the Clay

Properly preparing the clay is an essential step in creating high quality clay vessels. After the clay has been collected, it must be cleaned and prepared before shaping can begin. Here are some key techniques for preparing clay:

Cleaning – Fresh clay collected from the ground often contains impurities like rocks, roots, and debris. The clay must be broken up and soaked in water to dissolve and separate out any particles that are not clay. The clay and water mixture is then poured through a screen to catch rocks, roots, and debris.

Wedging – Wedging is the process of cutting, folding, and pressing the clay to form it into a uniform block. This removes air pockets and aligns the clay particles, resulting in a smooth consistency. Wedging evenly distributes moisture and improves the plasticity of the clay.

Kneading – After wedging, the clay must be kneaded to break up any remaining lumps or dry spots. Kneading warms the clay and makes it more malleable. It also further removes trapped air pockets.

Removing air pockets – Air pockets in the clay can lead to defects and cracking during drying and firing. In addition to wedging and kneading, a potter can use tools to pierce bubbles that rise to the surface of the clay. Smoothly working the surface also pushes out air pockets.

Taking the time to properly clean, wedge, knead, and de-air the clay results in a smooth, elastic, and responsive clay that is ready for shaping high quality vessels.

Shaping Methods

There are several techniques used to shape clay into vessels and pottery. The four main methods are pinching, coiling, slab construction, and wheel throwing.

Pinching

Pinching is one of the most basic and ancient methods of shaping clay. It involves taking a ball of clay and manipulating it with your fingers to form simple pottery like bowls, cups, and vases. Pinch pots are formed entirely by pinching the clay, applying pressure with fingers and thumbs to push the clay upwards and outwards.

Coiling

The coiling technique involves rolling clay into long ropes or coils, then stacking and bonding the coils together to build up the vessel walls. Coiling allows artisans to make larger and more complex shaped pottery. The clay coils are joined together using the scoring and slipping method – scratching horizontal lines into the coils, applying watered down clay, and smoothing the coils together.

Slab Construction

Slab construction involves flattening clay into thin sheets or slabs, cutting shapes out of the slabs, then joining those shapes together to form the vessel. Clay can be rolled out into slabs using a rolling pin, or pressed into slabs using a slab roller. The slabs are joined using the scoring and slipping technique. Slab construction allows for great variety in shapes and sizes of vessels.

Wheel Throwing

Wheel throwing involves sitting at a potter’s wheel and centering a ball of clay on the spinning wheel head. The artisan applies pressure with wet hands to shape the clay into forms like cylinders, bowls, vases as the wheel spins at high speeds. Wheel throwing requires practice and skill, but allows for symmetrical vessels with thin, evenly shaped walls. It is one of the most versatile clay shaping techniques.

Drying the Clay

After the clay vessel has been shaped, it must be thoroughly dried before firing. Clay contains water, so if not dried properly, the vessel can slump, crack, or even explode in the kiln. There are two main techniques for drying clay:

Controlled air drying: The clay work is left in open air to slowly dry. The key is regulating the air flow and humidity to prevent uneven drying. Fans can circulate air and dehumidifiers can remove moisture. The vessel should be rotated to ensure even drying. This process can take days or weeks depending on factors like climate, vessel size, and desired dryness level.

Using a drying box: The vessel is placed in an enclosed box designed to control temperature and humidity. Small electric heaters gently warm the interior while vents allow for air circulation. The box isolates the vessel from drafts that could cause cracking. Digital controls let you select an optimal drying environment. Drying boxes speed up the process to hours or days while minimizing distortion and cracks.

Applying Surface Treatments

After the basic form of a clay vessel is created, craftspeople often apply additional decorative surface treatments. There are several techniques that add color, texture, and visual interest to the vessel.

Burnishing involves rubbing and polishing the leather-hard surface of the clay with a smooth tool. This compresses the clay, making the surface shiny and smooth. Common burnishing tools include stones, glass, bones, seashells, and wood. The process brings out the natural color of the clay.

Slipping means applying a thin layer of fluid clay slip onto the surface of the leather-hard pot. The slip can match or contrast with the color of the underlying clay. Once dry, the slip provides color while the main clay body provides structure and strength. Multiple layers of colored slips can create patterns.

Enameling involves applying mineral pigments onto the clay surface and fusing them with heat. This creates colorful, glass-like effects. The enamel can be applied to greenware, bisqueware, or glazes. Common enamel pigments include colored glass powders or metal oxides.

Engraving and carving patterns, designs or images into the leather-hard clay is another decorative technique. Sharp tools are used to incise lines and remove clay in specific areas, creating texture and visual interest.

Firing the Vessel

Firing is one of the most important steps in creating clay vessels. It transforms the soft, fragile clay into a hard, durable material through a process of heat-induced chemical reactions. There are several key aspects of firing to understand:

Kiln Types

The most common kilns used for firing clay are:

• Electric kilns – These kilns use heating elements that generate a consistent, even heat. They allow excellent control over temperature and firing speed.
• Gas kilns – Fueled by propane or natural gas, these kilns produce a flame that provides strong, direct heat. They can reach higher temperatures faster than electric kilns.
• Wood-fired kilns – Fueled by wood, these kilns provide less control but can produce unique effects from wood ash and flame patterns.

Firing Temperatures

There are several standard temperature ranges used for firing clay:

• Low-fire – Up to 2,200°F. Produces a soft, porous clay.
• Mid-fire – 2,200°F to 2,300°F. Provides harder, less porous clay.
• High-fire – Over 2,300°F. Maximizes hardness and durability.

Firing Atmospheres

The kiln atmosphere impacts the clay’s final color and surface effects:

• Oxidation – More oxygen present, produces brighter colors.
• Reduction – Restricted oxygen, creates dark, smokey effects.

Understanding these key factors allows potters to achieve their desired results in firing clay vessels.

Glazing

Glazing is an important step in creating clay vessels that gives them an attractive, glossy finish and makes them nonporous. Glazes are made from a mixture of minerals and compounds that melt and fuse to the clay surface when fired at high temperatures in a kiln.

Common ingredients in glazes include silica, alumina, fluxes, and colorants:

• Silica, usually in the form of quartz or flint, is the main glass-former in glazes. It allows the glaze to melt and flow smoothly at high temperatures.
• Alumina, typically from clay, keeps the glaze stable so it doesn’t run off the piece. It also improves the strength and durability of the finished glaze.
• Fluxes like soda, potash, or boron lower the melting point of the glaze so it vitrifies at kiln temperatures. They allow the silica and alumina to fuse together.
• Colorants like metal oxides (cobalt, copper, manganese) give glazes their color and desired aesthetic effects.

Glazes can be applied to bisque fired clay using different techniques: dipping, pouring, brushing, or spraying. The viscosity of the glaze determines which method works best. Dipping and pouring tend to provide thicker coatings, while brushing and spraying allow more control over glaze thickness and location.

Firing glazes involves slowly increasing kiln temperature to around 2200°F to melt the glaze ingredients together into a smooth, glassy coating. The glaze firing schedule must align with the clay body to ensure good glaze fit and prevent defects like crazing. Fast firing can cause glaze faults like pinholing, while insufficient heat prevents the glaze from fully melting.

Final Touches

After firing and glazing, there are additional decorating and polishing techniques that can add flair and complete the clay vessel.

One popular finishing technique is incising, which involves etching or carving designs into the surface of the unfired clay using tools like knives, combs, or needles. This creates grooves and patterns on the surface. Incising allows the colored glazes applied later to pool inside the etched areas, producing decorative effects.

Burnishing is another finishing method where the unfired clay surface is polished to a sheen using a smooth tool. This compresses the clay, making the surface shiny and water-resistant. Burnishing can highlight carved decorative features as well.

Once fired, earthenware and stoneware pottery can be cold painted using mineral pigments mixed with an acrylic medium and water. Cold paints don’t require any additional firing. Potters use fine brushes to hand paint intricate designs. Gold leaf applications are also possible at this stage.

A final polishing using a soft cloth will remove any dust before the firing process and add protection from chipping. This finishing touch enhances the natural glossiness and brings out the clay’s inherent luminosity.

Conclusion

Clay vessels have been an essential part of human civilization for thousands of years. The techniques for making them have evolved over time, but the basic steps remain collecting clay, preparing it, shaping the vessel, drying it, decorating it, and firing it. While early vessels were made for purely utilitarian purposes, clay vessels today are still valued for their functionality and also as works of art.

The simplicity and availability of clay along with the immense creativity possible in shaping it have made clay vessels ubiquitous across cultures. From ancient Greek amphoras to Japanese tea ceremony cups to modern ceramic design, clay allows endless innovation. Yet the fundamental methods live on. Understanding the techniques involved in making clay vessels provides deeper appreciation of human ingenuity and artistic expression throughout history.