How to Process Natural Clay

Natural clay is a versatile material used for centuries in crafting pottery, sculptures, and countless other creations. It is a fine-grained, earthy substance made primarily of minerals such as aluminum silicates, and it forms through natural processes like weathering and decomposition of rocks over time. Natural clay deposits are found in riverbeds, hillsides, or beneath the soil, making it a widely accessible resource.

Before using natural clay for creative endeavors, it’s crucial to process it properly to remove impurities, achieve the right consistency, and enhance its workability.

Properly processed clay ensures a higher quality outcome, whether you are making artistic pottery or functional pieces. This article aims to provide a comprehensive step-by-step guide on how to process natural clay, covering everything from its extraction to its final preparation for crafting projects.

Understanding Natural Clay

Natural clay is a versatile material with unique properties ideal for various creative and functional applications. Multiple minerals, natural impurities, and its geological source define its composition and characteristics.

Composition of Natural Clay

The primary minerals found in natural clay include kaolinite, illite, and montmorillonite, each contributing distinct features to the clay. Kaolinite is known for its fine texture and low plasticity, making it suitable for porcelain production. Illite provides moderate plasticity, while montmorillonite is highly plastic and capable of retaining significant amounts of water, making it excellent for specific pottery techniques.

Additionally, natural clay can be categorized into earthenware, stoneware, and porcelain. Earthenware is porous and fired at lower temperatures, stoneware is dense and durable, and porcelain is highly refined with a translucent appearance.

Properties of Clay

Clay’s properties, such as texture, plasticity, and shrinkage, fluctuate based on its mineral content and impurities. Texture affects the ease of shaping, while plasticity determines its moldability. Shrinkage occurs as water evaporates during drying and firing, which must be carefully managed to prevent cracking. Impurities can hinder workability and alter firing results, so they need to be removed during preparation.

Where to Find Natural Clay

Natural clay deposits are commonly found in riverbeds, lake bottoms, and clay pits. High-quality clay is often located in areas with minimal contamination from organic matter or industrial pollutants. To identify usable clay in the wild, look for smooth, sticky soil with a fine grain and test its plasticity by rolling and shaping it.

Gathering and Preparing Clay from the Earth

Finding Suitable Clay Deposits 

To locate good clay deposits, identify areas like riverbanks, stream beds, or old lake basins where clay naturally accumulates. Look for clay that has a smooth texture, a fine grain, and a consistent color, often ranging from gray to reddish-brown depending on the type.

Test the plasticity of the soil by rolling it into a coil or ball; good clay will hold its shape without crumbling. It’s also crucial to ensure that the clay is clean and free from contaminants such as rocks, roots, and organic matter. This requires careful observation of the site and physical inspection of the material.

Extracting Clay from the Ground 

When extracting clay, safety and efficiency are paramount. Use tools such as shovels, spades, or hand trowels to carefully dig into the deposit without damaging the surrounding environment. Start by removing the topsoil, which usually contains organic material, to access the pure clay beneath. Dig small amounts at a time to avoid mixing impurities into your extracted material. Be mindful of erosion and refill holes to preserve the natural landscape when possible.

Cleaning Raw Clay 

Once the raw clay is extracted, the cleaning process begins. Large debris like stones or roots can be removed by hand-picking or sieving the material through a fine mesh screen. The clay can be soaked in water for finer cleaning and stirred to separate dirt, sand, or other impurities. After this, the clay is poured off, and the sediment settles, leaving behind a clean, workable material ready for pottery or other uses.

How to Process Natural Clay: Slaking and Soaking the Clay 

Why Slaking is Important 

Slaking is a critical step in the clay preparation process. Its purpose is to break down the raw clay into smaller pieces, making it easier to process and refine. This softening step ensures that the material is pliable, uniform, and free of hard spots, which could otherwise compromise the quality of the final product. 

The Process of Slaking 

The material must first be submerged in a large container or trough filled with water to slake clay. The pieces of raw clay, ideally already broken into smaller chunks, are left to soak for a sufficient amount of time. Typically, this involves letting the clay sit undisturbed for 24 to 48 hours to allow it to soften completely. This soaking period enables water to fully penetrate the clay, breaking it down and preparing it for further refinement. 

Creating a Slurry 

Once the clay has softened adequately during slaking, it transforms into a smooth, liquid-like mixture known as slurry. The ideal consistency of the slurry resembles that of thick cream, providing an easy-to-work medium for various applications such as pottery, casting, or mold-making. This ensures that the clay is homogeneous and free of inconsistencies, making it more manageable and versatile. 

Draining Excess Water 

After achieving the desired slurry consistency, the next step is draining excess water. This can be done by pouring the slurry through a fine mesh or screen to separate the usable clay from the watery residues. This final step ensures that the clay is in optimal condition for further processing and shaping, guaranteeing a high-quality end product.

Drying and Kneading the Clay 

Once the usable clay has been separated from excess water, the next step is drying it further while maintaining its workability. A common technique involves pouring the slurry onto plaster slabs.

Plaster is highly absorbent and helps draw out the remaining moisture from the clay at a controlled rate. Alternatively, the slurry can be spread on a clean, non-porous surface and left to air dry until it reaches a manageable consistency. Care must be taken not to over-dry the clay during this stage, as it can become brittle and prone to cracking. Keeping the clay slightly pliable ensures it remains optimal for kneading. 

Kneading the Clay 

Kneading is a crucial step in preparing the clay for shaping and crafting. This process involves working the clay with your hands to remove any trapped air bubbles and ensure a uniform consistency.

To knead, the clay is repeatedly folded, stretched, and pressed. Tools such as a rolling pin can assist in this process, but many artisans prefer the tactile feedback of using their hands. Kneading enhances the clay’s texture and makes it more elastic and responsive to various shaping techniques. 

Identifying the Right Consistency 

Before proceeding with molding or other applications, verifying the clay’s workability is necessary. Properly prepared clay should be smooth, soft, and free of lumps. A simple plasticity test can be performed by pressing a small piece of clay between your fingers. The consistency is ideal if it holds its shape without cracking or crumbling. 

Re-wetting and Re-kneading 

If, during the kneading process, the clay begins to dry out too much, small amounts of water can be added. This is done gradually to prevent over-saturating, as excessive water would make the clay too sticky and hard to handle. Similarly, if the clay is too wet, leaving it to air dry for a short period can help achieve the desired consistency. This balance ensures the clay remains versatile and ready for creative uses. 

Forming and Shaping the Clay 

Basic Techniques for Shaping Clay 

Several fundamental techniques for shaping clay are suitable for both beginners and seasoned artists. Hand-building methods such as pinching, coiling, and slab-building are ideal for creating smaller projects. Pinching involves molding clay between fingers to form basic shapes, while coiling allows artists to build forms layer by layer using rolled-out clay ropes. Slab-building involves flattening clay into sheets that can be cut and joined to create structures.

For more intricate or uniform designs, a pottery wheel is often used. This technique requires practice but offers precision and symmetry for advanced creations. 

Shaping Tips for Beginners 

For beginners, maintaining even and consistent thickness in clay walls is crucial. Uneven surfaces can lead to weaknesses during drying or firing. Tools such as rolling pins or guides can assist in achieving uniformity. Additionally, eliminating air bubbles is vital to prevent cracks or breakage—this can be done by thoroughly wedging the clay before shaping. 

Making Clay Body Adjustments 

Clay composition may be adjusted to suit specific project requirements. Grog, which consists of fired clay particles, can be mixed into the clay body for added texture or stability. Similarly, altering the clay’s plasticity or strength can prepare it for either delicate detailing or structural work, ensuring it aligns with the artist’s intended purpose.

Drying and Firing Clay 

Drying Process 

After shaping the clay, proper drying is essential to prevent cracking or breakage. Slow and even drying is key, as rapid moisture loss can cause the clay to warp or crack. Drying your clay at room temperature is best, avoiding direct sunlight, heaters, or other intense heat sources.

Covering the piece loosely with plastic or a damp cloth can help regulate the drying process, ensuring the moisture levels decrease gradually across the entire piece. Depending on the size and thickness of the clay piece, drying time can vary from several days to a few weeks. 

Firing in a Kiln 

Once thoroughly dried, the clay can be fired in a kiln. There are two common types of kilns to choose from: electric and gas. Electric kilns are often preferred for their precision and ease of use, while gas kilns provide greater control over the firing atmosphere, which can influence the final appearance of the piece.

The firing process typically begins with bisque firing, where the clay is heated to 1,800-2,000°F to become durable and porous. Afterward, glaze firing may be done if a decorative or functional coating is applied, often at a higher temperature around 2,200°F. Each step requires careful temperature control to achieve optimal results. 

Common Mistakes to Avoid

Not Cleaning the Clay Properly 

Before beginning any project, ensure that the clay is thoroughly cleaned. Impurities such as roots, stones, or other debris can compromise the integrity of the final piece. These foreign objects may cause cracks, breakage, or distortion during shaping or firing.

Improper Slaking or Kneading 

Slaking and kneading are crucial steps to prepare clay for use. If the clay isn’t fully broken down and wedged properly, inconsistencies in texture may arise. This can lead to weak spots or cracks forming in the final product, especially under the stress of firing.

Over-Drying or Under-Drying the Clay 

Maintaining even moisture levels in the clay is vital for successful results. Over-drying can make the clay brittle and prone to breaking, while under-drying might cause the piece to warp or crack as moisture escapes unevenly during the firing process. Always ensure a balanced drying environment.

Conclusion 

Processing natural clay is an art that requires attention to detail and patience. The key steps include gathering clean clay, soaking it to break it down, kneading to achieve a consistent texture, shaping your desired form, drying it evenly, and finally firing it to solidify the piece.

Understanding how to process natural clay is essential for achieving durable and beautiful results. Consistency and perseverance are critical, as working with clay can present unique challenges with each batch. Don’t hesitate to experiment, as each project offers an opportunity to develop new skills and insights into the rewarding process of working with natural clay.