While the art of pottery may appear enchanting, its beauty is underpinned by a methodical step-by-step process. A thorough understanding of the various phases involved in shaping clay and the subsequent ceramic creation is crucial. Whether you’re new to pottery or simply seeking a more defined understanding of pottery, this guide offers a professional outline, providing insight into the precision and expertise needed to craft exceptional ceramic works.
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Clay Preparation
The initial stage of pottery creation involves obtaining a workable clay material. In earlier times, artisans were compelled to excavate their own clay from nearby deposits, as they lacked alternative choices. A number of potters continue to unearth their own clay, experiencing a profound bond with the earth through this method.
However, this activity demands considerable effort and presents significant challenges for contemporary city-based potters. Consequently, the majority now purchase pre-prepared clay bodies from one of the many ceramic material suppliers usually available in their region.
When buying pottery clay, essential aspects to evaluate are its category (earthenware, stoneware, porcelain), the required firing temperature (cone), its texture (grog content), and its malleability (workability). Your final decision should align with your kiln’s specifications, the intended purpose of your creation, and your personal proficiency.
The inherent plasticity of clay—its capacity to be spread, extended, and moulded into new configurations without breaking—is a fundamental property utilised in techniques such as throwing, pinching, and the formation of clay sheets and coils. This plasticity characteristic is of considerable importance. Nevertheless, it is not the only quality to consider, as clay itself is an exceptionally diverse material. It is crucial to understand that certain types of clay are more easily shaped for particular processes than others.
For instance, a clay that performs well for press moulding might prove difficult to throw, and a clay that throws effectively could be challenging to join in slab building. The joinability of the clay, for example, is vital for methods like slab building, coiling, two-piece press moulding, and the application of handles. Therefore, the specific properties of the clay significantly influence how the final object can be formed.
Wedging
Wedging is a technique for manually blending clay by rotating and compressing a lump of the material on a table. Its main purpose is to ensure the clay achieves a consistent texture and to eliminate any trapped air bubbles. This process is critical because air pockets in the clay can cause pieces to explode inside the kiln as air expands during firing. Such an event would not only ruin your own work but also potentially damage other items nearby in the kiln.
While the terms “wedging” and “kneading” are frequently used interchangeably, they actually refer to slightly different processes. Both are crucial clay preparation methods designed to achieve a uniform consistency, align the clay’s particles, and eliminate any air pockets that could lead to cracking or explosion of ceramic pieces during the drying and firing stages.
Kneading: This initial stage involves softening the clay, much like kneading bread dough. It entails pressing, folding, and rotating the clay repeatedly to ensure uniform moisture distribution, remove any firm or dry clumps, and enhance its pliability.
Wedging: This is a specialised and energetic blending technique primarily designed to expel air pockets and densify the clay. Typical approaches include:
- Ram’s Head Wedging: In this method, you propel the clay forward and downward using the palms of your hands, subsequently drawing it back. This action forms an internal pattern within the clay, reminiscent of a ram’s head complete with two horns.
- Spiral Wedging: This technique employs a twisting and rolling movement. Considered a more advanced approach, it compels trapped air to exit in a spiral fashion, proving particularly efficient for larger blocks of clay.
Forming
Once the clay is fully wedged, it is ready to be formed using a range of methods, including slab, wheel, coil, pinch, or moulding. These techniques can be applied individually or combined. These methods are employed to mould the damp clay before it is subjected to drying, firing in a kiln, and glazing.
Hand-Building – Hand-building is shaping clay into an object solely with one’s hands. This technique also includes more specialised construction methods, such as coil building and slab building, and it frequently complements other ceramic forming approaches.
Slab Building – Slab construction is a technique that involves flattening clay into sheets, either manually or with tools such as a slab roller or a rolling pin. These resulting slabs are then used to build objects, most often using a mould. Depending on the aesthetic or design needs, the clay can be utilised from its wet state up to leather-hard.
Coiling – This method is arguably the most straightforward for crafting clay vessels and sculptures. Clay is formed into long ropes, which are then progressively stacked in a spiral, each new coil securely joined to the one beneath it, until the intended height and contour of the piece are formed. It is an excellent technique for beginners, providing significant insight into the behaviour and limitations of clay when wet.
Throwing – When envisioning the creation of pottery, most individuals likely picture wheel throwing. Pottery throwing is the technique of shaping wet clay into symmetrical containers on a spinning potter’s wheel. It merges the centrifugal force generated by the rotating wheel with the skilled hand movements of the potter to sculpt, extend, and refine the clay, producing functional or decorative pieces like bowls, cups, and vases.
Slip Casting – Slip casting is a method that uses custom-designed moulds into which liquid clay is poured to create the mould’s inner form. The clay is introduced and allowed to rest, enabling the mould to absorb some of its water content. This action causes a thin, more rigid layer of clay to solidify against the mould’s contours. After a few minutes, the surplus slip is drained from the mould, and the piece is set aside to dry. Once sufficient time has passed, the mould is opened, and the hollow clay shape is carefully extracted. After removal, any mould seams are scraped smooth, and the item is left to dry further until it is prepared for bisque firing.
Drying
The moment a clay bag is unsealed, the drying process commences. Drying is the removal of moisture. In the drying process, the clay dehydrates, sheds moisture, hardens, and starts to contract.
Drying relies on three principal elements: heat, which promotes evaporation; the moisture content of the surrounding air, whether natural or controlled; and the flow of air over the surface, which replaces humid air with drier air (F Hamer and J Hamer*).
In pottery, drying is a fundamental process that prevents warping and structural damage, as drying frequently leads to shrinkage, which can cause cracks and material distortion. It is essential to master the drying process to achieve strong, flawless pottery or prevent potential explosions during kiln firing.
As clay dries, moisture evaporates, leading to the piece’s contraction. Achieving uniform drying ensures the entire object shrinks consistently, preventing internal stresses, cracks, or potential explosions during kiln firing.
Several vital considerations highlight the necessity of proper drying, such as:
Preventing Structural Flaws: When different sections of your pot dry at varying rates, the clay contracts unevenly. This differential shrinkage creates internal tension, which can lead to deformation or the appearance of fissures.
Mitigating Kiln Catastrophes: If pottery is fired while still retaining trapped moisture, the intense heat transforms that water into steam. As steam expands rapidly, it requires an escape route; confined steam can cause the ceramic piece to fracture or violently disintegrate within the kiln.
Securing Glaze Application: Bone-dry clay provides a much more amenable surface for applying underglazes and glazes. Any residual dampness might lead to an inconsistent coating or cause the glaze to detach during firing.
Leatherhard Stage
Once your clay creations have spent several hours (or days) drying, typically covered in plastic, they will achieve a state of partial desiccation known as leatherhard. This particular drying phase is marked by the evaporation of water, causing the clay to become rigid and less pliable. It presents an ideal opportunity to refine the object, such as sculpting away surplus clay, attaching handles or other ornamental features, or shaping a bowl’s footring.
Crucially, this represents your final opportunity to alter the piece’s form! Recognising this specific stage is extremely vital. Should the clay dry past this point, any subsequent modifications to its shape become impossible. The leatherhard stage is considered optimal for turning pottery and affixing handles, even though working at a less firm consistency might offer certain aesthetic benefits depending on what you want.
Greenware
Ceramic pieces that have been fully formed but still require further drying before they can be fired. This indicates that all its water has been lost to evaporation, leaving it inflexible. Attempting to bend it will cause it to break. You cannot incorporate any new material into it, nor can you carve anything from its surface.
Having not yet undergone the chemical transformation of firing, greenware remains brittle, entirely soluble in water, and can be reprocessed into workable clay if desired. Therefore, being highly fragile, greenware is vulnerable to damage from any bump, which may result in fracture or deformation.
Bisque Firing
Once your pieces have fully dried to the greenware stage on the racks, they can be fired. This firing phase involves heating to at least 600°C. This high temperature hardens the pottery, making it considerably easier to handle without damage during the subsequent glazing procedure.
However, clay fired at this temperature still maintains its porous nature. The porosity of a material indicates its capacity to absorb liquid. In this context, the water component of the glaze is absorbed by the permeable bisque ware, leaving the glassy elements of the glaze deposited on its surface. Therefore, the bisque firing primarily serves to simplify the glazing application.
The entire bisque firing process spans about two or three full days from commencement to completion. The kiln is loaded with the dry greenware, then ignited and set to a low temperature to further dry the pieces. Accelerating the firing process too rapidly during this initial phase can easily cause the work to explode. Then the kiln’s temperature is incrementally increased, and the heat reaches the desired temperature, whether low fire (Cone 04 or 06) or high fire (Cone 8 to Cone 10), depending on the clay that was used.
The kiln is then deactivated and permitted to cool down slowly. Usually by the end of the second day or third day, the kiln is opened, the bisque ware is removed, and the ceramic pieces can be handled and examined by the potter.
Glazing
Glaze (a compound of ground glass, various clays, pigments, and water) firing can be accomplished through two primary methods. One method involves the simultaneous maturation of both the glaze and the ceramic body. The other method applies glaze to a body that has already reached its mature state, with the firing process exclusively affecting the glaze. Each of these techniques comes with its own distinct advantages and disadvantages.
For the first method, also called single firing or raw glaze, you apply glaze to unfired clay and complete the entire firing process in one cycle. However, this approach demands specific techniques and clay to prevent the ceramic pieces from warping or cracking. It saves energy and time, but it offers a higher risk of breakage, and as mentioned, crawling or pinholing. The decision is yours depending on your desires.
In the second method, the glaze is applied to the fired bisque pottery through methods like dipping, pouring, spraying, brushing, sponging, or a combination of them and heated to a high temperature. The intense heat causes the glaze ingredients to melt, creating a smooth, vitreous surface that fully fuses with the clay body, making the piece functional, resilient, and visually striking.
Glaze firing initiates significant physical and chemical changes in both the ceramic body and the glaze as the kiln reaches its maximum temperature. These changes include,
Burnoff: As the kiln gradually warms, it incinerates any lingering organic substances and expels any remaining moisture.
Melting: The mineral components of the glaze (comprising silica glass-formers, fluxes, and stabilisers) start to liquefy and coalesce.
Bonding: Upon reaching the highest temperature, the liquefied glaze dissolves a thin stratum of the clay body, thereby creating an enduring bond between the glaze and the clay’s surface.
Cooling: Subsequently, the kiln gradually cools, allowing the molten glaze to solidify into a resilient, smooth, glassy finish.
ESSENTIAL TIP: Prior to firing, always ensure you wipe or sponge off any glaze from the bottom of your ceramic ware. If glaze remains on the pot’s base, it will liquefy and irrevocably fuse your creation to the kiln shelf.
Final Thoughts
In essence, the intricate journey of pottery making, encompassing everything from initial clay forming to the final glazing and firing, is a testament to human creativity and skill. Each step, meticulously executed, contributes to the transformation of raw material into a finished piece. This comprehensive process inherently underscores the profound value of engaging in the art of pottery, where the metamorphosis of raw earth into practical artwork necessitates patience, critical thinking, and ongoing growth through its techniques and imperfections. Have a happy pottery!
(*) The Potter’s Dictionary of Materials and Techniques, Sixth Edition, Frank Hamer and Janet Hamer, Herbert Press, reprinted in 2024).
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