Ceramics: Part One
Is it Earthenware, Stoneware or Porcelain? Part One of Two: The Ceramic Building Process

I often purchase a single bowl from a ceramic artist, adding to my eclectic collection. I like how the different weights, surface textures, colors, and designs reflect the signature of a serious potter. Most of what I’ve purchased is difficult to discern between earthenware, stoneware, or porcelain. I generally have to ask at the time of my purchase, although occasionally the color or weight gives me the answer. So I’ve made it my mission to learn a little about clay types, or clay bodies as they are referred to in the ceramics industry, the ways in which clay is formed, and the tools in which it's worked, fired, and colored. Paula West invited me to her ceramic studio on San Juan Island in discovery of these differences. Right away I learned the ceramic industry has a full language all its own, involving clay attributes, firing temperatures, and aesthetic components.

There are primarily three broad categories for clay bodies: earthenware, stoneware, and porcelain. First, the differences between them have to do with the specific components from which they are made. Secondly, the result of the mixtures directly affects the range of the firing temperatures, referred to as “the cone” temperatures. And lastly, it’s the aesthetic components of the final product made by the combination of the clay body mixture and the firing temperatures that further defines the categories of earthenware, stoneware, and porcelain.

Clay bodies can range from off-the-shelf standards to highly specialized blends that are made-to-order according to individual specifications. Serious pottery studios that can invest $4,000 for a clay mixer can produce combinations to suit their individual creative impulses. Alternately, for a fee you can have your own mix made to your specification from pottery supply stores found regionally in either Seattle or Tacoma. A color base is also established during the ordering process, ranging from reds to buff and white.

What makes clay bodies so specialized is their kiln firing temperatures, and it is the recipe of the clay properties mixed together that defines their cone, or firing temperatures. The earthenware clay body is considered a low fire, vitrifying at lower temperatures of roughly 2000 degrees or a “cone 04.” Earthenware is considered the most common clay body and perhaps the easiest to form or manipulate, with less tendency towards cracking in the kiln during firing as the porcelain clay body. Stoneware and porcelain clay bodies can be purchased in either a mid-firing range of a “cone 05” or “cone 06,” which is roughly 2232 degrees, or in high firing “cone 10” of roughly 2381 degrees. The offering of mid-firing clay allows folks who have electric kilns that only fire up to a range of “cone 08” to work stoneware and porcelain clay bodies as well.

After determining what your clay body selection will be for a final ceramic piece–clay type for firing temperature, or the cone rating systems, and color range–we can get into the creative process of forming the clay, by using either a potter's wheel or hand-building.

Potter's wheels come in all varieties, and they range in price from home-made items done by the mechanically inclined to spiffy showroom models. The price for new beginner/intermediate hobbyist wheels on the Internet range from $350 to $1000 plus shipping, and will generally be dictated by the weight capacity, ranging from 15 pounds of clay on the wheel to 150 pounds, then add the motor quality needed for continuous motion. The heavy-duty professional grades have weight capacities of anywhere between 100 lbs. to unlimited weight capacity with a heavy-duty 2-horsepower motor. Paula’s wheel shown in the image was purchased used and is medium in size with perhaps a 50-lb. capacity.

Hand-building tools are much less of an investment if you don’t have access or need of a potter’s wheel and can hand-work your clay. Hand-building methods are described as pinch-forming or coil-forming, rolling a slab, or even a combination of formats using an individual’s ingenuity. Tools used for either hand-forming or wheel-forming include such basics as your hands and a sponge and a “rib” (also known as a scraper) used for smoothing a surface and made of materials such as rubber, wood, or metal. Trimming tools are known basically as sculpting tools and are used to create lines or textures. Additional texture tools can be found through the use of unusual objects that depart a texture pattern on a surface. Once you have a shape completed to your satisfaction you’re ready to go on to the remaining two processes of coloring and kiln firing. Notice the half-moon items in the image of the tools; those are the smoothing "ribs" or scrapers.

Color is added either by using a colored slip or a glaze, and it can be done either while the piece is wet on the wheel and freshly formed or when it has hardened. Hardness is determined as either leather-hard, meaning it still has a minimum of moisture and can be carved, or bone-dried, which is, as the term suggests, from air drying. There is a low temperature firing known as bisque firing to pull out moisture so the piece can be handled for glazing. It’s at this juncture that ceramics can take another radical departure, which serves to further separate their uniqueness in a wide variety of color finishings and firings.

The application of color and the range of kiln firing techniques will be covered in Part Two in July. I'll cover the process of ceramics, where we’ll look at Raku firing, Hot Ice Crystallization, and other unique ceramic finishings and firings.

If this inspires you to learn more first-hand there are a number of ceramicists on the islands who give workshops and have open studio time for both children and adults. Paula West will be opening her studio for visitors during the summer months–see her studio and work by visiting her web page www.sanjuanartistcommunity.com/west .