From Earth to Art: The Complete Guide to Sourcing Ceramic Clay
Have you ever held a ceramic mug or a beautiful piece of pottery and wondered where it all began? The smooth, earthy material in your hands has an incredible story that starts deep within the ground. This is the behind-the-scenes journey of how various types of clay are sourced and transformed into the versatile medium artists love.
The Geological Origins of Clay
Before we dig into specific types, it’s helpful to understand what clay actually is. At its core, clay is a product of time and geology. It consists of fine-grained mineral particles that are formed from the weathering and erosion of feldspathic rock, like granite, over millions of years. Water, wind, and ice break down these rocks, carrying tiny particles away.
Geologists classify clay deposits into two main categories, and this distinction is key to understanding why different clays are found in different places.
- Primary Clays: These clays are found at their original site of formation. They haven’t been moved by natural forces, so they are very pure, with large, coarse particles. The most famous primary clay is Kaolin, the essential ingredient for porcelain.
- Secondary Clays: These are clays that have been transported from their original location by water, wind, or glaciers. This journey grinds the particles down, making them finer and more plastic (easier to shape). Along the way, they pick up mineral impurities like iron oxide, which gives them their color. Earthenware, stoneware, and ball clay are all secondary clays.
Sourcing Earthenware: The Earth's Most Common Clay
Earthenware is one of the oldest and most common types of clay used by humans. It is known for its reddish-brown color and its porous nature after being fired at low temperatures.
How It’s Sourced: Because it’s a secondary clay that hasn’t traveled far from its parent rock, earthenware deposits are found all over the world. They often lie close to the surface, making them relatively easy to extract. You can find rich deposits in riverbeds, floodplains, and even in your own backyard in some regions.
The characteristic red color of most earthenware comes from iron oxide and other mineral impurities it collected during its short journey. Historically, potters would source their earthenware locally, digging it straight from the ground. Commercial suppliers today still source it from large surface deposits, but they will process it to ensure consistency. For example, a major supplier like Standard Ceramic Supply sources its popular “Redart” clay from deposits in Ohio. This clay is then screened and processed to create a reliable product for potters.
Sourcing Stoneware: The Versatile Workhorse
Stoneware is the durable, go-to clay for functional pottery like dinnerware and mugs. It is fired at a higher temperature than earthenware, which makes it strong, dense, and non-porous. It comes in a variety of colors, from light gray and tan to dark brown.
How It’s Sourced: Stoneware is also a secondary clay, but it has typically traveled a longer distance than earthenware. This extended journey by water washes away more impurities and grinds the particles down, resulting in a less contaminated and more plastic material.
Stoneware deposits are found deeper in the earth than earthenware. Extraction often involves mining from larger, more established pits and quarries. Regions with a history of stoneware production, like the Westerwald region of Germany or areas in the American Southeast, are built upon significant natural deposits. Commercial clay bodies, like B-Mix from Laguna Clay Company, are often a blend of several different sourced stoneware clays, plus other minerals, to achieve specific working properties and firing results.
Sourcing Porcelain: The Pursuit of Purity
Porcelain is prized for its elegance, strength, and brilliant white, translucent quality when fired at very high temperatures. Its unique properties come from its primary ingredient, kaolin.
How It’s Sourced: Unlike the other clays, the key component of porcelain is a primary clay. Kaolin, also known as “china clay,” is mined directly from the locations where it was formed millions of years ago. Because it was never transported by water, it remains exceptionally pure and free of contaminating minerals like iron. This purity is what makes it fire to such a brilliant white.
Kaolin is a globally important mineral and is extracted through large-scale open-pit mining operations. Major sources of high-quality kaolin are found in Cornwall, England; the “Kaolin Belt” in Georgia, USA; and, most famously, the mountains near Jingdezhen, China, which is considered the historical birthplace of porcelain. After being mined, the raw kaolin is washed, screened, and refined to remove any non-kaolin minerals before being sold to ceramic suppliers.
Sourcing Ball Clay: The Secret to Plasticity
Ball clay is the unsung hero of the ceramics world. It is rarely used on its own because it shrinks dramatically when drying. However, its incredible plasticity and strength make it an essential additive to stoneware and porcelain clay bodies.
How It’s Sourced: Ball clay is an incredibly fine-grained secondary clay. It formed in ancient swamps and river deltas, where the clay particles settled along with carbonaceous materials from decaying plants. This organic matter contributes to its dark gray color in its raw state and its exceptional plasticity.
It is sourced from specific geological basins through surface mining. The world’s most significant deposits are found in Devon, England, and in the Kentucky-Tennessee region of the United States. Companies like Old Hickory Clay Company in Kentucky specialize in mining and processing these clays. Potters and industrial manufacturers add a small percentage of ball clay (typically 10-25%) to their recipes to make the final clay body more workable and easier to shape on the potter’s wheel.
Frequently Asked Questions
What is the difference between a natural clay and a clay body? A natural clay is a clay sourced directly from a single deposit in the earth. A clay body is a recipe created by a ceramic supplier. It is a carefully controlled blend of one or more natural clays plus other minerals like silica (for strength) and feldspar (to help it melt and vitrify in the kiln). Most potters today use commercially prepared clay bodies for their consistency.
Can I dig my own clay for pottery? Yes, you can! This is often called “wild clay.” You can find it near riverbeds, lakes, or construction sites. However, wild clay needs to be processed to be usable. This involves drying it, crushing it, soaking it in water (a process called slaking), and then sieving it through screens to remove rocks, roots, and other impurities. It’s a rewarding process but requires significant effort and testing.
Is clay a sustainable resource? Clay is an abundant natural resource, but like any mined material, its extraction has an environmental impact. The large-scale mining operations for kaolin and ball clay can disrupt ecosystems. Many modern mining companies are required to follow land reclamation plans to restore the mined areas after the deposits are exhausted. For individual potters, using clay responsibly and recycling scraps are important sustainable practices.