What Is The Process Of Forming A Clay Vessel On A Pottery Wheel?
Wheel throwing is the process of using a pottery wheel to form clay vessels and other ceramic objects by hand. It involves centering a lump of clay on a rotating pottery wheel, opening up the center, raising the walls, and shaping the clay into the desired form. Wheel throwing takes practice to master but allows potters to quickly and symmetrically shape clay into uniform pieces. It is one of the most common forming techniques in pottery and enables the creation of a wide variety of vessel shapes and sizes. This article will provide an overview of the full wheel throwing process, from selecting and preparing the clay to raising and refining the walls and completing with drying and firing the finished piece.
Selecting and Preparing the Clay
The first step in making pottery on a wheel is choosing the right clay. Potters select clay based on factors like plasticity, strength, color, and intended firing temperature. Plasticity refers to how easily the clay can be shaped without becoming too sticky or cracked. More plastic clays are better for throwing on the wheel. The clay also needs enough strength to hold its shape during forming and firing. Choosing a clay formulated for the intended firing method is crucial – for example, stoneware and porcelain are fired at higher temperatures than earthenware.
Once a suitable clay type is chosen, proper conditioning and preparation ensures the clay has the right consistency for wheel throwing. Clays often contain small air pockets that can cause cracking or exploding in the kiln, so kneading or “wedging” is done to remove air bubbles and evenly distribute moisture. The clay is cut into chunks, slammed on a wedging table, and folded onto itself repeatedly. A uniform consistency allows the clay to center well on the wheel head and form cleanly into an even-walled vessel.
Wedging the Clay
Wedging is a critical step in preparing clay before throwing on the wheel. It involves repeatedly cutting, folding, and kneading the clay to achieve an even moisture content and remove any air pockets.
Start with a lump of clay and cut it in half with a wire tool. Then slam the two halves together onto the wedging table. Using the palms of your hands, push the clay away from you, fold it back toward yourself, and push down to compress it.
Continue cutting, slamming, folding and compressing until the clay feels smooth, uniform and free of cracks or air bubbles. Well-wedged clay should hold together but not feel sticky or stiff.
It’s important not to wedge too little or too much. Under-wedging can lead to air pockets in the finished piece, while over-wedging makes the clay tough to center. With practice, you’ll get a feel for when the wedging is complete.
Centering the Clay
Once the clay is securely attached to the wheel head, the next step is to center it. Centering the clay is crucial for being able to raise uniform walls and craft a symmetrical pot.
To center the clay, place both hands on either side of the clay and apply even pressure as the wheel spins. Do not press too hard or the clay will flatten out. Apply enough pressure for the clay to evenly move under your hands. Make adjustments as needed until the clay is centered and not wobbling or leaning to one side.
Use a wooden rib tool to further refine the centering while the wheel spins. Hold the rib firmly against the outside of the clay at a 45 degree angle and apply pressure while moving the tool up and down. This will trim away any uneven sections. Check for centering from all sides of the clay.
Continue re-centering and adjusting the clay until it stays perfectly centered while the wheel is in motion. The clay should feel solid, stable and balanced before moving on to raising the walls. Rushed centering will lead to an off-center pot that will collapse. Taking the time to properly center is fundamental to creating a successful pot.
Opening the Clay
Once the ball of clay has been properly centered on the pottery wheel, the next step is to open up the solid ball of clay to form an interior space. This is done by using one or both thumbs to gently press down into the center of the ball of clay while it is still spinning. The potter exerts light pressure with the thumbs while slowly widening the space to form an opening in the clay. It’s important not to push down too hard or too quickly, as that may cause the sides of the clay to collapse. Creating a conical shaped interior space allows the clay walls to be evenly supported as they are raised up. The opening should be widened until the desired size and shape is achieved based on the type of pot or vessel being thrown. The potter must ensure the walls maintain an even thickness throughout the opening process. Having an opened interior space with relatively thin and stable walls is crucial before the next step of raising the walls. This opening forms the foundation upon which the rest of the pot will be built through pulling up the walls.
Raising the Walls
Once the clay is centered on the wheel and has been opened up, you can begin raising the walls. This takes practice and coordination. Place both hands inside the cylinder of clay, with your fingers rested gently on the walls. Apply even pressure as you slowly pull the walls upwards. The goal is to raise the walls evenly without thinning and distorting the clay. Move both hands in unison, keeping the same rhythm. Don’t raise the walls too quickly or pull too hard. Go slowly and focus on keeping the walls uniform. The height and width of the piece will determine how high you can raise the walls before they become too thin. Taller pieces require thicker walls than shorter pieces. As the walls get higher, use your thumbs to support them from outside while your fingers support them from within.
Forming the Base
Once the clay walls have been raised to the desired height, it’s time to shape the bottom of the vessel. This process is known as forming the base. The goal is to create a flat, even bottom for the pottery piece.
Start by using one hand inside the vessel to support the base while the other hand shapes it from the outside. Use a rib tool or your fingers to gently press the clay at the bottom, working in a spiral pattern from the center outward. Apply even pressure as you smooth the clay to create a flat surface.
Be careful not to make the base too thin, as this could cause it to crack or break when firing. An appropriate thickness for the base is around 1/4 inch. Use calipers to measure and maintain consistent thickness.
Once the bottom has been pressed flat, use a wooden modeling tool to further refine the shape and smooth out any bumps or ridges on the surface. Take care to keep the base centered on the wheel as you form it.
Shaping a properly flat base takes practice and a delicate touch. Don’t be discouraged if your early attempts have bumps or divots. With time and experience, you’ll be able to shape perfectly flat and even bases for your pottery.
Refinement
Once the basic shape of the vessel has been formed, the clay is still quite soft and needs refinement to complete the look. This stage involves careful smoothing, trimming, and detailing of the overall form.
Smoothing out the clay walls, rim, and base is an important step. Any lines, wrinkles, or uneven areas are gently smoothed out using a few different tools – sponges, ribs, metal scrapers, or just fingers. The goal is to achieve an even, uniform surface texture. Sponges work well for softening curved areas, while metal scrapers are good for smoothing flat surfaces. A damp sponge can also be used to lightly moisten drier areas so they blend with wetter sections.
Trimming cleans up the foot or base of the piece using looping trimming tools. This step defines the curve between the walls and base and removes any excess clay or uneven bits. The aim is for a neat, symmetrical foot. Trimming also helps refine the rim, neatening and evening it out so the lip has a clean, finished look.
Detailing involves adding any decorative elements like ridges, lines, edges, etc. These details give the piece interest and complements the form. Details can be made by carving into the clay with tools, or adding on extra bits of clay. The clay surface can also be altered by imprinting textures with stamps, brushes, or sponges. Extra bits of clay like handles or spouts can be carefully attached at this stage as well.
Being methodical at each step allows the clay vessel to be transformed from a rough lump into a refined, elegant form. Patience and practice help potters master the skills needed to bring out the best in each unique piece.
Drying and Firing
Before a piece can be fired in a kiln, it must be allowed to dry thoroughly first. Rushing the drying process can lead to flaws and cracks as the moisture tries to escape too quickly. Slow, even drying is key.
Once wedged and formed, a clay piece should be allowed to air dry completely. Drying time can range from a few days for small pieces to weeks for large pieces. Wrapping pieces in plastic can slow down drying if it is occurring too rapidly. Placing pieces in a cool, ventilated area out of direct sunlight will allow moisture to evaporate from the clay slowly.
The clay needs to be bone dry before firing. To test dryness, clay artists often hold pieces up to their cheeks to feel if any coolness remains. A moisture meter can also quantify remaining moisture. If moisture remains in the center, cracks and explosions can occur in the kiln.
Once fully dry, the clay is ready to be bisque fired in a kiln according to the clay type specifications. Bisque firing further hardens the clay before applying glazes and finishing firing. After glazing, the final firing will melt the glazes to create the finished ceramic ware.
Conclusion
Forming a clay vessel on a pottery wheel involves multiple steps that require skill, patience, and practice. The potter must carefully select and prepare the clay, centering it on the wheel before slowly raising the walls to create the desired shape. The base is formed to complete the basic vessel structure before refinements are made. Once the initial drying process is complete, the vessel undergoes a final firing to harden and finish the clay. With dedication to mastering the fundamentals of wedging, centering, raising, and more, a potter can produce beautiful and functional pottery using this time-honored process.
