Choosing the Right Clay
When it comes to pottery, choosing the right clay is crucial for achieving the desired results. With so many options available, it can be overwhelming to navigate the world of clay. This guide will walk you through everything you need to know about buying clay for pottery, from understanding the different types of clay to selecting the best clay for your projects.
Clay is available almost everywhere and is inexpensive. It has multiple transitional states; when moist, it is pliable and elastic, and can be moulded into any shape. It can be incised or scraped when it reaches the consistency of chocolate, after drying slightly. As the water dissipates into a brittle state, the material dries further, depending on its thickness and the relative humidity. At this juncture, it can be re-softened by applying water. However the clay is formed, it will not be permanent until it is heated to extremely high temperatures.
There are several types of clay available for pottery, each with its own unique characteristics and suitability for different projects. It is essential to understand these differences to choose the right clay for your needs.
1. Earthenware clay
This clay is porous and fires at a lower temperature. It is ideal for beginners and is commonly used for making decorative pottery, tiles, and sculptures. Earthenware clays are low-fire clays. Low-fire clay is fired at temperatures ranging between 804°C and 1,154°C. When potters discuss the cone at which a particular variety of clay is fired, they are referring to the pyrometric cone system. This is a method for classifying the temperature and the effect of time with the firing.
2. Stoneware clay
This clay is denser and fires at a higher temperature, resulting in sturdy and durable pottery. It is suitable for functional items like bowls, mugs, and plates. When wet, stoneware clays are often grey and plastic. Their fired hues range from pale grey and beige to medium grey and brown. Fired colours are significantly affected by the type of firing. Stoneware clays are typically fired at high temperatures, around 1,186°C - cones 5 to 10. Stoneware clays are referred to as “Stoneware” because the fired items exhibit characteristics similar to those of stone (hard, dense surface with varying hues). After maturing in a kiln, stoneware should form strong bonds with its glazes and be impermeable. It is durable and tolerant during the throwing and firing phases. Stoneware is a common type of clay used by production potters.
3. Porcelain clay
Known for its delicate and translucent appearance, it is often used to create elegant and refined pottery. However, it can be challenging to work with due to its fine and less forgiving nature. Pure kaolin (kaolinite, or china clay), ball clay, feldspar (used as a flux), and quartz (silica) are the main components of porcelain. Mixing the body of porcelain clay with various minerals reduces the firing temperature and improves its workability. Porcelain holds fluidity and can be manipulated even when extremely thin to create translucent, delicate forms because it is composed of such minute particles. As a consequence of its lack of plasticity, it can crack and deform during the drying and firing processes due to its optimal density not being reached until the clay nears its melting point.
4. Ball clay
Ball clay is the most plastic clay and contains very limited mineral impurities. It contains a large percentage of kaolinite and quartz, with around 10-25% mica. Ball clays occur naturally as very thin mineral-rich sediments or deposits. Ball clays lose colour on firing. At the greenware stage, it is grey. After being fired, it acquires a faint buff hue. When properly fired, it produces a delicate white colour, making it popular among potters. Ball clays are frequently utilised for floor tiles, toilets, basins, vases, and tableware due to its high plasticity and binding capacity. Ball clay by itself is typically too fine and slippery for use. It can be used for wheel throwing but is mainly used in slip casting and as an additive to other clay bodies.
Factors to consider when selecting clay
1. Intended use
Think about what you want to create with the clay. Are you looking to make functional items like plates and bowls, or are you more interested in sculptural pieces? Different types of clay have varying strengths and textures, so it’s essential to choose one that suits your desired end result.
2. Workability
Consider your level of experience and comfort working with clay. Some clays are easier to manipulate and shape, making them more suitable for beginners. Other clays require more skill and experience to handle effectively.
3. Firing temperature
Take into account the firing temperature of the clay. If you have access to a specific kiln or firing method, make sure the clay you choose can withstand those temperatures.
All in all there are quite a few elements to consider when choosing clay. But fear not, if you are unsure as to what you need, just ask the Supervisor at your pottery session. SPCI carries a wide range of clays at discount prices and if we don’t have the one you want, we can usually get it in for you. Otherwise there are clay suppliers in town that also carry a range of clays, however you will be paying a retail markup on the price with these businesses.
Edited courtesy of an article by Moss 51 Art+Design
