How Do You Make Pottery Clay Malleable?

Pottery clay, also known as ceramic clay, is a material used for making pottery, ceramics, and sculpture. The clay becomes workable and malleable when mixed with the right amounts of water and other substances. Making clay malleable involves understanding clay composition, properly mixing and preparing the clay, and using techniques to keep it in an ideal state for working.

The purpose of making clay malleable is to be able to form it into desired shapes and have it hold that form. Malleable clay is flexible, but also has enough body and elasticity so that it does not become overly sticky. Properly prepared clay is easy to mold, shape, roll, press, coil, and throw on the potter’s wheel while still sturdy enough to retain the formed shape.

Gathering Clay

The first step in pottery clay production is finding and extracting natural clay deposits. Clays suitable for pottery are usually found in regions with waterlogged, low-lying terrain where sediments have collected over time. Common clay sources include river banks, lakeshores, coastal regions, and glacial deposits.

Clay extraction typically begins by identifying exposed clay beds. Test samples can determine if the clay has appropriate properties for firing and forming. Productive deposits warrant more systematic prospecting to map the extent and composition. Test pits and borings provide subsurface data to delineate the clay bed.

Once adequate clay reserves are proven, surface mining operations begin. Bulldozers remove overburden soil and rock to expose the clay. Excavators and frontend loaders dig into clay seams, loading it into trucks for transport. Water cannons help dislodge consolidated clay. Mining continues sequentially until the deposit is exhausted.

Mined clay contains impurities like sand, silt, gravel, and organic matter. Initial washing and sieving eliminates larger particles. The clay then goes into sedimentation tanks where gentle agitation allows denser clay particles to settle out from finer silts. Further refinement and blending creates the optimal composition for pottery.

Processing the Clay

Once the clay has been gathered, it must go through several processing steps to remove unwanted materials and prepare it for pottery making. This involves cleaning, crushing, and screening the clay.

Cleaning refers to removing contaminants like roots, rocks, and organic material. This is often done by hand, picking out larger particles. The clay can also be mixed with water into a slurry which allows heavier particles like rocks to sink to the bottom, while the clay remains suspended in water.

After initial cleaning, the clay is crushed and ground down to break up chunks and clods. Traditionally this was done by hand with tools like a mortar and pestle. Now electric grinders and crushing equipment are often used. The clay must be pulverized into a fine powdery texture.

Finally, the ground clay is screened to remove remaining pebbles, grit, and irregularities. Screens with different sized mesh are used to filter out particles. This screening ensures the clay has a uniform consistency with no large pieces remaining. The end result is a smooth clay powder ready for further processing and addition of other ingredients.

Analyzing the Clay

Once the clay has been processed, it’s important to test its properties before using it for pottery. The key properties to analyze are plasticity, shrinkage, and porosity.

Plasticity refers to how easily the clay can be shaped without cracking or crumbling. Clays with good plasticity will hold their shape when molded and maintain smooth surfaces without tearing. Plasticity can be tested by wedging or kneading a piece of clay and observing how well it bends and stretches without breaking apart.

Shrinkage refers to how much the clay shrinks as it dries and is fired in a kiln. Clays with high shrinkage can warp and crack after drying if the forms are not designed to accommodate shrinkage. To test for shrinkage, roll a coil, measure its length, allow it to dry completely, and re-measure to see how much it shrank. The more it shrinks, the higher its shrinkage rate.

Porosity describes how porous or watertight the clay is when fired. Low porosity is desirable for functional pottery that will hold liquids. Test porosity by forming a small pinch pot, allowing it to dry and firing it. Then, fill it with water and see if the water seeps through the clay walls. The less water that seeps, the less porous the clay is.

By thoroughly analyzing these key properties, potters can select the best clay for their needs and make adjustments if necessary.

Adjusting Clay Composition

The composition of clay can be adjusted to optimize its properties for pottery making. Fillers, fluxes, and plasticizers are commonly added to clay to improve its workability, durability, and firing qualities:

Fillers – Materials like grog (ground up fired clay), sand, vermiculite, perlite, and sawdust can be added as fillers. Fillers reduce shrinkage and crack formation during drying and firing. They improve clay body strength and shape retention.

Fluxes – Fluxes like feldspar lower the vitrification temperature of clay so glazes melt and fuse with the clay body at lower kiln temperatures. They enhance the development of glassy phases in the clay upon firing.

Plasticizers – Materials like bentonite clay help improve the plasticity and workability of pottery clay. Plasticizers bind clay particles together and allow the clay to become smooth, flexible, and malleable when mixed with water.

Carefully proportioning and incorporating fillers, fluxes, and plasticizers enables potters to formulate clay bodies suited for their desired shaping methods, firing temperatures, and aesthetic qualities.

Kneading the Clay

Kneading is a crucial step for making clay malleable and increasing its plasticity. There are two main kneading methods: mechanical and hand kneading.

Mechanical Kneading
Mechanically kneading clay involves using a pugmill, which is an industrial machine consisting of two counter-rotating shafts with attached blades. The clay body is fed into the pugmill, where the blades cut, fold, and reform the clay into a uniform mass. This intensive mechanical action aligns the clay particles, thoroughly mixes in water, removes trapped air pockets, and creates a homogeneous consistency.

Hand Kneading
Hand kneading is done by repeatedly cutting, slamming, and folding clay on a stable work surface. This manual process mimics the pugmill and realigns clay particles to increase plasticity. Simple hand tools like rib boards and rolling pins can also assist with kneading moist clay. Compared to mechanical kneading, hand kneading takes more time and effort but allows direct touch and feel for judging clay consistency.

Clay Storage

Properly storing clay is crucial for maintaining its moisture content and malleability between uses. Here are some clay storage tips:

Wrap your clay in plastic and place it in an airtight plastic container. Plastic almost completely seals out air, preventing the clay from drying out. Place a damp sponge or moist paper towel in the bottom of the container so the clay doesn’t dry out.

For short-term storage (less than 2 weeks), you can simply wrap clay tightly in plastic wrap or place it in a zip top plastic bag with the air squeezed out. Squeeze out air each time after using to prevent drying.

Avoid storing clay anywhere it will freeze or get very hot, as extreme temperatures can affect its malleability. Store clay at room temperature between 60-80°F.

Check your stored clay periodically. If it starts to dry, remove it from the container and knead in water. The exact amount will depend on how stiff your clay has become.

Reconditioning Clay

When working with clay that has been stored for awhile, it’s important to recondition it before use. This involves re-kneading the clay to make it malleable again. Often, stored clay will become quite dry and stiff. Here are the steps to properly recondition clay:

• Take the clay out of its storage wrapping/container

• Cut or break the dry clay into smaller pieces

• Add small amounts of water and knead it into the clay to bring the moisture level back up

• Continue adding small amounts of water and kneading until the clay reaches the desired consistency and malleability

• If too much water is added, continue kneading to distribute the moisture evenly or let the clay sit wrapped in plastic to absorb excess moisture

With some kneading effort, dried and stiff clay can be reconditioned for use in pottery and sculpting projects. Adjusting the moisture level is key. Store unused reconditioned clay properly by wrapping in plastic to maintain consistency.

Shaping Methods

There are several techniques used to shape clay into pottery, with the three main methods being throwing, handbuilding, and molding.

Throwing refers to using a pottery wheel to shape the clay. This takes practice to learn how to center the clay on the wheel and manipulate it into the desired form using your hands as the wheel spins. Skilled potters can create uniform pieces with thin walls using this method.

Handbuilding involves shaping the clay freeform using your hands, as well as tools like ribs and loop tools. Types of handbuilding include pinch pots, coiled pots, and slab pots. This method allows you to shape the clay without the use of a wheel.

Molding uses a form, mold, or cast to produce a piece. The clay can be pressed into an existing mold so it takes on the shape. Molds can be used to reproduce the same shape over and over. The clay can also be draped over an existing form, like a bowl or vase, before removing the form so the clay keeps the hardened shape.

Conclusion

Shaping malleable clay into pottery is an creative process that requires an understanding of clay’s composition and behavior. By gathering, processing, analyzing and properly storing clay, potters can recondition it to an optimal malleable state for throwing and handbuilding techniques. Kneading helps make clay more plastic and responsive to shaping methods. The ability to make clay malleable with the right consistency and moisture content is key for sculpting beautiful, functional ceramic pieces from pots to tiles and figurines. Mastering these clay preparation techniques allows full creative expression through the versatile medium of clay.