How Does The Potter Prepare The Clay To Make Pots?

Table of Contents

Gathering the Clay

Potters have various options when it comes to sourcing the clay required for making pottery. While in the past, potters would dig and gather clay locally, today most potters purchase commercially prepared clay.

Clay can be gathered from local sources such as river beds, construction sites, fields or mountainsides. However, the quality and properties of locally sourced clay can vary greatly. Digging and processing clay locally requires time and effort.

For most potters today, purchasing pre-processed clay from art supply stores or online retailers is the easiest option. These clays are professionally prepared for optimal consistency and firing results. Common types available include earthenware, stoneware, porcelain, and specialty clays suited to particular techniques.

When selecting clay, it’s important to consider the clay body, intended firing temperature, color, and suitable applications. Having a reliable and high quality clay source ensures the potter’s work will be consistent batch to batch.

Processing the Clay

Properly processing the clay is a crucial step in preparing it for pottery making. Once dug from the ground, raw clay contains many impurities like small rocks, sand particles, roots and organic matter. The clay must be cleaned and purified before it can be worked into a usable state.

The initial processing involves soaking the clay in water to soften it and allow the impurities to separate. The clay soak can take anywhere from several hours to several days depending on the clay composition. As the clay absorbs water and softens, any rocks, roots or debris will settle to the bottom of the soaking container.

After soaking, the clay is poured through a screen to catch the larger particles. The filtered clay is then wedged or kneaded to further mix the clay and force out any remaining air bubbles and impurities. Wedging involves cutting the clay into chunks and slamming it against a flat surface to compress it. Kneading involves folding and pressing the clay repeatedly like working bread dough. Either process blends the clay thoroughly and results in a uniform, smooth consistency.

Multiple cycles of soaking, screening and wedging/kneading may be required depending on the initial state of the raw clay. Careful processing removes any complicating impurities and allows the clay properties to shine through when building pottery.

Achieving Desired Consistency

Achieving the proper consistency of prepared clay is one of the most important steps before beginning to shape pots. The amount of moisture content in clay affects its plasticity and workability. As clay dries it becomes stiffer and less yielding to manipulation, and when too wet it becomes overly sticky and soft, making it difficult to maintain form.

The ideal consistency is when clay maintains its shape when formed but is still soft and plastic enough to bend and indent without cracking or resisting. This allows the potter to shape smooth, uniform pieces that hold crisp lines and details without slumping or becoming misshapen as they dry.

To reach the desired plasticity, water is incrementally incorporated into the prepared clay body and kneaded in evenly. The clay is periodically tested by shaping a ball and observing how well it holds form without sticking or cracking at the seams. The potter adds water in small amounts at a time, continuing to wedge and knead until the ideal moisture content and consistency is achieved. The prepared clay should feel smooth, flexible, and moldable without being tacky or sticky against the hands.

Mastering moisture control when preparing clay is an essential skill. The wheel-throwing process and quality of finished ware relies heavily on the plasticity of the clay body. Achieving optimal consistency takes practice and familiarity with different types of clay. With experience a potter learns to quickly discern the right amount of moisture content to reach that ideal state of flexibility and workability.

De-Airating the Clay

One of the most important steps in preparing clay is de-airating it by removing any air bubbles trapped in the clay. Air bubbles can weaken the structural integrity of finished pottery pieces and cause them to explode or crack when fired in the kiln. Potter’s have developed several techniques over the centuries to effectively de-airate clay.

Wedging is likely the most common method of de-airating clay and involves cutting the clay into chunks and then slamming it against a wedging table to force out air bubbles. The clay is then folded onto itself, pressed together, and slammed down again in a repetitive process that evenly distributes moisture and removes pockets of air.

Another technique is called slamming or dropping which involves throwing chunks of clay forcefully against a solid work surface. The impact causes vibrations that dislodge air bubbles which are then worked out of the clay. Some potters also use a plaster bat as the surface to increase absorption of moisture.

Commercial de-airating pugmills provide an automated and efficient way to de-airate large quantities of clay. A pugmill contains rotating blades that cut through the clay under pressure to remove air bubbles as the clay is extruded out.

When clay is properly de-aerated, it becomes more plastic and easier to work with. Potters are then able to successfully shape intricate forms without getting cracks and weak spots after firing. Taking the time to adequately de-airate clay is a simple but essential step that enables creating durable, high-quality ceramic pieces.

Storing the Clay

Proper storage is crucial for keeping clay workable over time. Fresh clay straight from the bag or pug mill contains moisture that needs to be retained. Allowing clay to dry out will cause it to become stiff, crack, and be difficult to wedge or throw on the potter’s wheel.

To prevent moisture loss, prepared clay should be stored in thick plastic bags or plastic wrap. Press out any air pockets before sealing the clay completely. Plastic helps trap moisture and prevent evaporation. For long term storage, double wrap the clay or place it in air-tight buckets with tight lids.

Check stored clay periodically and spray with water if it starts to stiffen. Light misting will rehydrate the surface before the moisture penetrates through the lump. Knead well to evenly distribute the water. For very stiff clay, allow more time for thorough soaking before using.

With proper sealing and occasional re-wetting, clay can be stored for weeks or months while retaining its plasticity and workability. Keeping clay wrapped and hydrated allows potters to prepare large batches for future projects.

Choosing Clay Color

One of the most important decisions when preparing clay is choosing the ideal color for the potter’s planned project. There are several options when it comes to coloring clay:

Natural clay comes in a range of earthy hues from red and brown to grey and white, depending on its mineral composition. For example, stoneware clays are often grey whereas red earthenware clays get their reddish tone from iron oxide content. Potters can utilize these natural clay colors in their finished works.

Adding ceramic stains is a simple way to tint natural clay. Stains are concentrated pigments made from metal oxides that mix into the clay body before throwing. Cobalt produces blues while manganese creates pinks and purples. Stains allow subtle yet vibrant colors.

For more intense, opaque color, powdered pigments can be integrated into the clay. Common pigments are Mason stains, underglazes, and mineral pigments. Similar to stains, powdered pigments permeate the entire clay body for rich, uniform color. Pigments allow unlimited options for vibrancy and tone.

By understanding the range of natural clay colors, stains, and powdered pigments, potters can choose the ideal coloring method and clay hue to complement their planned piece and artistic vision.

Choosing Clay Texture

The texture of clay is an important consideration when preparing it for pottery. Clay comes in smooth, coarse, grogged, and additive options that each have their advantages.

Smooth clay contains no additives and has a silkier, finer texture. It’s easy to throw on the wheel and ideal for creating delicate pieces. However, smooth clay is prone to cracking and warping as it dries.

Coarse clay contains tiny particles of sand or grog that create tooth and traction. The gritty texture makes coarse clay easier to handle and shape by hand. It also shrinks less than smooth clay. Coarse clays are good for handbuilding techniques.

Grogged clay has larger particles like crushed bricks or tiles added to the clay body. The grog gives the clay more structure and strength, reducing shrinkage and warping. Grogged clay is ideal for large sculptures and garden pots that need to withstand weathering. The texture can make grogged clay more difficult to throw on the wheel.

Clay can also be mixed with additives like paper, sawdust, or sponge to create interest. For example, paper creates fibrous pockets within the clay and sawdust burns out during firing for a pitted surface. The additives alter the clay’s properties and texture.

Consider the desired working properties, finished look, and intended purpose when deciding on clay texture. The options allow potters to create diverse pieces from the same clay body.

Understanding Clay Properties

Clay can be categorized into different types based on key properties that affect how the clay behaves and the final outcome when fired. Mastering these properties allows the potter to select the optimal clay for any project.

Plasticity

Plasticity refers to how easily clay can be molded and shaped without cracking or crumbling. More plastic clays have high clay and water content, making them very flexible to work with. Less plastic clay contains more non-clay ingredients like sand or grog and is stiffer and more difficult to shape.

Firing Range

Clays are designed to be fired at specific temperature ranges. Lower-fire clays mature from 1000-2200°F while high-fire clays need 2200-2400°F to fully fuse and vitrify. Firing clay at the proper range results in a strong finished piece that has been properly sintered.

Shrinkage

As clay dries and is fired, it shrinks in size. Clays advertise their shrinkage percentage, usually between 7-15%. Knowing the shrinkage allows proper planning when designing to account for how firing will reduce the piece’s dimensions.

Porosity

Porosity determines how watertight the finished clay will be after firing. More porous clay remains slightly absorbent, while less porous clay becomes vitrified and impermeable during firing. Porosity depends on the clay composition and the maximum firing temperature reached.

Preparing Specialty Clay Bodies

Potters often customize clay bodies to achieve specific properties and effects in their finished pieces. One way to modify clay is by mixing in additives and inclusions. Common additives include:

Grog – Grog refers to pre-fired clay that has been ground into a granular powder. Adding grog makes clay more porous, reducing shrinkage and making the clay body stronger and more resistant to cracking and warping while firing. Grog comes in different particle sizes from fine to coarse. Coarse grog is used for handbuilding sculptures while fine grog works well for throwing on the wheel. Typical grog additions range from 10-30% by weight.

Paper Pulp – Paper fibers like recycled newspaper can be blended into clay as a combustible additive. As the paper burns out during firing, it leaves behind empty spaces making the clay more porous and lightweight. Paper pulp allows for faster drying and reduced shrinkage. It also weakens the clay so it is more suitable for handbuilding vs wheelthrowing. Up to 50% paper pulp can be added for specialty clay bodies.

The potter experiments with small test batches first to evaluate the effects of different additives and ratios. Once the desired clay properties are achieved, the clay ingredients must be thoroughly mixed together in the proper proportions. Mixing is done using a pug mill to evenly distribute the additives without introducing air pockets into the clay. Well-mixed custom clay bodies result in fewer defects and more consistent performance for the potter’s specialized needs.

Troubleshooting Clay Issues

One of the most common issues potters face is cracking, slumping, or clay becoming unusable while working. There are several techniques to remedy these problems and rescue your clay:

Fixing Cracking or Slumping Clay

If your clay begins to crack or slump while throwing on the wheel, it likely means the clay is too wet. To fix this:

Let the clay sit for a short time to let some moisture evaporate.
Wedge or knead the clay again to redistribute the moisture and bind it back together.
Add a small amount of dry clay or grog to absorb excess moisture.
Do not add water, as this will only make the problem worse.

Try throwing again in short intervals to see if cracking persists. Letting the clay rest overnight can also help. If the clay continues to crack, you may need to reconstitute it with a new batch of clay.

Salvaging Unworkable Clay

If your clay becomes too wet, dry, or hard to work with, it can be saved:

For clay that is too wet, let it dry out partially and wedge in some dry clay or grog.
For clay that is too dry, mist it lightly with water and knead thoroughly to distribute moisture.
For stiff clay, wedge vigorously to warm it up and make it more pliable.

Test the clay’s consistency and adjust moisture as needed until it reaches the ideal flexible, smooth texture for throwing. Let the clay rest if it begins cracking again. With patience and persistence, you can often rescue clay and avoid wasting it.