This article will explore the various ways potters can source clay for their craft. It will cover digging clay from the earth, including identifying suitable locations, obtaining necessary permissions, and testing the clay’s properties. The article will also discuss purchasing clay from suppliers, comparing different types of clay bodies, and considering factors like cost, availability, and intended use. Finally, it will touch upon the option of reclaiming and recycling clay, outlining the process and benefits of this sustainable practice. The article aims to provide a comprehensive guide for potters seeking to find the right clay for their pottery projects, whether they prefer the adventure of wild clay or the convenience of commercially prepared options. One of the key decisions in pottery is selecting the right type of clay, as it significantly influences the final outcome of the piece. With various clays available, each possessing unique characteristics, it’s essential to understand the distinctions to create successful and satisfying pottery projects.
Understanding Clay Types
There are several slightly different types of clay used for different types of pottery, but clay can be classified into 6 main types that are used commonly among potters. The 6 main types of clay are earthenware clay, stoneware clay, ball clay, fire clay, porcelain clay, and air dry clay. Earthenware clay has been used by potters throughout history and is probably the earliest form of clay to be used. This type of clay is very sticky, has high plasticity and so it is easy to manipulate and work with. The high level of plasticity in this type of clay means that it won’t slump or collapse when being worked into pottery. Earthenware clay has a composition of iron, and a few other mineral impurities, which work to give it its unique properties. Earthenware clay is a versatile and popular type of clay known for its rich, warm colors and lower firing temperatures. Basic earthenware, often called terracotta, absorbs liquids such as water. Earthenware can be made impervious to liquids by coating it with a ceramic glaze. You can learn about different glazing techniques here.
Stoneware clays appear white or grey when water is added to them. Stoneware also has a high plasticity and so is easy to work with. Stoneware does not come from the erosion of a parent rock – stoneware clays contain mineral impurities such as silica, feldspar, ball clay, and quartz. As stoneware does not result from the direct erosion of specific parent rock, it often contains impurities. Some of these impurities are silica, feldspar, ball clay, and quartz. Stoneware clay is a durable and versatile type of clay known for its high firing temperatures. Stoneware is a dense, strong, and impermeable clay that is normally only partially vitrified (fired to the point that it is not porous). Stoneware may be vitreous or semi-vitreous depending on the temperature it is fired to and is normally glazed. Stoneware is fired at temperatures ranging from 2,000° to 2,400° F. These high temperatures partially or completely vitrify the clay. Unlike porcelain, which is almost always white, stoneware is usually colored gray or brownish because of impurities in the clay; potters can make stoneware with multiple different clay colors today.
Porcelain clays are, as their name suggests, used to make porcelain pieces. It is typically white in color and so lends itself to bright white pottery pieces. Porcelain clay is sometimes known as kaolin as this is what it is made of. It is almost purely made up of kaolin clay, with occassional amounts of quartz and feldspar when manufactured. It can withstand extremely high temperatures. The structure of this clay allows it to withstand the high temperatures in a kiln and when fired it becomes non-porous and very hard. There are three types of porcelain ceramics: hard-paste, soft-paste, and bone china. Hard-paste or “true” porcelain is the most common type. “True” porcelain is fired at very high temperatures such as cone 10 (2345℉ or 1285℃) and yields sturdier objects. It contains added minerals to the kaolin, usually feldspar or mica. Soft-paste porcelain is the least common type. Bone china has mostly replaced true porcelain in modern times. It’s the strongest kind of porcelain.
Ball clays are more practical when mixed with other types of clays. Ball clay is mined from the soil or a parent rock. Much of the clay body is composed of organic matter but it also contains small amounts of alkaline earth metals like magnesium and calcium. Ball clay generally comes in the form of a white powder. Ball clay is known for its plasticity, fine particle size, and high organic content. Kaolinite, mica, quartz, and other organic matter make up ball clay, also known as “plastic clay.” This clay type was originally used for floor and wall tiles but is also great for creating plates, vases, mugs, and similar pottery projects. Additionally, it’s commonly used to strengthen and add plasticity to other clay bodies. Fire clay has an extremely high firing range (beginning at 1600°C). It can endure extremely high temperatures and so is perfect for making extra hard pottery products. As a result of its resistance to high temperatures, fire clay is perfect for use in pottery or ceramic products that require resistance to high temperatures such as bricks for kilns, ovens etc. Air-dry clay is a type of clay that dries and hardens naturally in the air without the need for baking or firing in a kiln. Unlike traditional clay types, such as earthenware or stoneware, air-dry clay does not require high-temperature firing in a kiln or baking in an oven. Air-dry clay is typically softer and more pliable than traditional ceramics clay. While air-dry clay is not as durable as fired ceramics, it can still produce sturdy and long-lasting pieces when handled with care. To ensure your clay is safe, take time for clay recycling.
Tools of the Trade
Aprons are a potter’s best friend, especially if they want to protect their clothing from potential damage. Potter’s needles are slender steel tools with needle-like heads and, occasionally, handles. Another essential tool for your pottery arsenal is a wire clay cutter or cut-off wires. A fettling knife looks like a regular knife, except it boasts a flexible blade that tapers to a point. Ribs are great for smoothing and finishing clay on the wheel. Scrapers, however, are used to remove clay instead of shaping and smoothing it like ribs. Ribbon and loop tools typically boast wooden or plastic handles. Any potter will tell you that modeling tools are a must-have for your pottery endeavors. Sponges are an effective tool in that they’re multi-purpose, making them an invaluable addition to your pottery toolkit. A pottery brush is another tool that boasts a variety of uses, especially concerning the decoration of your clay creations. Pottery calipers essentially perform the same function as regular calipers. They measure the inner and outer dimensions of your clay creations, precisely where they’ll join with other parts of a set. Other general pottery tools include knives and rasps, needle and scoring tools, sanding and abrasive tools. Decorating pottery tools include faceting tools, screen printing stencils, stamps and texture tools, texture rollers, sgraffito tools, and slip trailers and applicator bottles. Throwing pottery tools include calipers and measuring tools, needle tools, ribs and scrapers, throwing sticks, pot lifters, and handle and spout makers. Trimming pottery tools include turning tools and ribbon & wire loop tools. Handbuilding & sculpture tools include handheld extruders, modeling tools, scoring tools, tile & hole cutters, rolling pins, paddles, slab molds & tools, and beveling tools.
Handbuilding Techniques
Handbuilding is an ancient pottery-making technique that involves creating forms without a pottery wheel, using the hands, fingers, and simple tools. The most common handbuilding techniques are pinch pottery, coil building, and slab building. To make a pinch pot, one inserts a thumb into a ball of clay and continually pinches the the clay between the thumb and fingers while rotating to thin out and raise the height of the vessel. Pinching can deliver a pleasingly organic look, but can also yield beautiful, refined results. In my own work hand building clay I often pat out a small round slab to place in the bottom of a puki in order to form the bottom of a pot. Scraping the walls with a sharp edge can help to refine the overall vessel shape, thin wall thickness and leave a more consistent surface. The simple pinch pot is among the easiest and most basic of hand built clay techniques. To get started take a fist sized lump of clay and insert your thumb into the center. Slowly pinch and stretch the clay around that initial hole to create your desired shape. Coil building is a forming method that uses ropelike coils of plastic clay, assembled in successive courses to build up wall of vessel or sculpture. Rolling clay coils is a funny thing, it seems to come naturally to some people while others struggle. This is an essential coil pottery technique so if you plan on doing coil building this is worth practicing with an eye on perfecting. Reach inside the form and press it out into the desired shape, this is how round bellied jars, lifelike cultures and many other shapes are achieved. When making coil pottery there is no technique as important as your bonding pinch. The flat pinch is a coil pottery technique used to thin the pot wall. This is usually accomplished with the thumb and forefinger on opposite sides of the pot pinching together. This is the key pinch used in coil pottery to give the vessel shape. Just adding and thinking coils will not result in an attractively shaped pot, probably something akin to a flower pot. The compression pinch allows the potter to bring the walls in, forming narrow mouthed jars and other shapes.
Glazing Techniques
Pottery glaze lets you add unique colors and textures to your pieces prior to firing. Dipping is the easiest way to cover pottery and is done by most at some point. This form of glazing will give the finished piece a smooth look and fine texture. You can either dip your piece into the glaze twice as a base layer before decorating, or, to achieve a more solid look, you can dip the piece more often to create a thicker layer. By flowing the glaze over the piece that you plan on firing, you are working on the pouring glazing method. As you pour, the piece will absorb some of the glaze creating an even layer on the interior and exterior of the piece. With the style of dripping, you aren’t trying to cover the whole piece. Once you have a base layer of glaze, you can start to apply the dripping technique to your piece with a squeeze bottle to add decorations or other colors that wouldn’t have been there before. Brushing can be used as both a base layer and for decorating. Picking the right brush size is important. Large flat brushes are great for larger pieces, and small, round-tip brushes are better for patterns or designs. You’ll want to have a good amount of glaze on your brush as you paint to avoid streaks in the glaze on your piece. You also want to take into consideration different brush stroke directions. For example, if you paint your first layer of glaze horizontally, you’ll want to paint vertically for the next layer and so on. A banding wheel is also needed to rotate the pottery while you’re spraying the glaze since you can’t move the gun around much. This glazing method is best for laying down a precise base layer that you typically can’t get with pouring, brushing, or other methods. To make your own at home, here’s a guide on how to make your own glaze for pottery.
Firing Methods
Firing clay transforms it from its humble, soft beginnings into a new, durable substance: ceramic. The temperature needed to transform soft clay into hard ceramic is extremely high and is usually provided by a kiln. Firing is the process of bringing clay and glazes up to a high temperature. This process is usually accomplished in two steps: bisque firing and glaze firing. Bisque firing refers to the first time newly shaped clay pots, or greenware, go through high-temperature heating. Typical ceramics firing occurs in two stages: bisque firing and glaze firing. During the first firing – bisque – greenware transforms into a durable, semi-vitrified porous state where it can be handled safely while being glazed and decorated. The second firing occurs after the artist has applied glaze to the piece, hence the name, and is typically faster than bisque firings because most of the water has already been driven out of the clay.
