I love making ceramic beads. And while most ceramic artists will tell you that glazes are their favorite obsession, and though I like them too, I like clay just about as much. I am a clay
hoarder collector. While on road trips, anytime I happen to be near a clay supplier, I am sure to stop in and check out the clay they have in stock, and will usually leave with 3 or 4 bags.
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| A variety of fired clay body samples; from clay obtained in the southeast US. (Stone Mountain Clay). |
What is Clay vs. Clay Body?
First it's important to understand to distinguish (raw) "Clay" from "Clay Body"...
"Clay is a natural product dug from the earth, which has decomposed from rock within the earth's crust for millions of years. Decomposition occurs when water erodes the rock, breaks it down, and deposits them. It is important to note that a clay body is not the same thing as clay. Clay bodies are clay mixed with additives that give the clay different properties when worked and fired; thus pottery is not made from raw clay but a mixture of clay and other materials."
~ Encyclopedia.com / Pottery.
Ingredients are added to raw clay to stabilize workability and firing properties. This changes the clay from simple raw "clay" to a "clay body":
"The term 'clay body' will be used to indicate a mixture of clay like materials with other inclusions for a specific ceramic technique. In other words, a 'clay body' may have several different kinds of clay, fluxes, silica, grog, and other ingredients for color,plasticity, warping, cracking, shrinkage, porosity, firing temperature,texture and etc. A single clay from the natural world will seldom have all of the characteristics which the potter will need for a particular ceramic technique. The principles of forming a body are the same regardless of whether it is earthenware, stoneware, or porcelain.
~ Basic Notes on Clays and Clay Bodies by Robert Fromme.
Types of (Raw) Clay
There are 2 major groupings of raw clay from which clay bodies are created:
- Primary Clay, or Residual Clay is clay is formed at the site of the parent rock. It is less common than Secondary (Transported or Sedimentary) clay, but generally whiter, free from impurities. Because this clay is broken down by ground water, etc. and not transported, particle size is mixed (no opportunity for sorting or grinding) and the clay is usually not very plastic, and are refractory. Most kaolins are primary clays.
- Secondary Clay has been transported from multiple sources by water (alluvial), or wind (aeolian), which sort particle sizes, or by glacier (glacial), which may grind but has uneven particle sizes. Many secondary clays contain organic (carbonaceous) and other impurities (iron, quartz, mica, etc.). Some of the more plastic kaolins are secondary clays. Other secondary clays: Ball Clay, Stoneware Clay, Fireclay, Earthenware Clay, Slip Clays, Volcanic Clays.
~ Clays and Clay Bodies by Linda Arbuckle.
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| The rolling cart where I keep my most-used clay bodies upstairs in the main studio. |
Types of Clay Bodies
There are 3 types of clay bodies used by most ceramic artists. They are typically commercially mixed. Each of these have distinct characteristics and firing routines:
- Earthenware fires from about cone 08‐02 (1751°F‐2048°), and can be white, buff, orange, red, or brick. Usually not as vitrified as high‐fired clays. Tends to warp and melt before it vitrifies. Less shrinkage than more vitrified clays, often used for sculpture. General absorption range 5‐10 %. Addition of 0.5% barium carbonate will react with the soluble salts in earthenware bodies, esp. terra cottas, and prevent scumming on dried and bisqued wares by forming insoluble compounds of barium and soluble salts.
- Stoneware can be from medium range (cone 4‐6, 2170‐2230°) to high temperature (cone 10, 2350°), white to dark in color, medium to coarse in texture. General absorption range for stoneware is 1‐5%.
- Porcelain is a high‐temperature body (cone 10‐11), very dense and fine‐grained, vitrified, translucent when thin, white to pale blue‐grey in reduction, white to creamy in oxidation. General absorption range 0‐2%. If a texture is desired, molochite, a porcelain grog, is usually used to maintain white color. Very white porcelains are often short (low in plasticity.)
~ Clays and Clay Bodies by Linda Arbuckle.
I purchase and use clay bodies from all three groupings, however, my predominant choices are stoneware and porcelain. I currently have around 35-40 different clay bodies in my studio, but typically only use about 6-8 on an ongoing basis. When I have the urge to try something new I'll open up some of the others to give them a spin. I keep smaller samples of each clay body in small labeled tubs near my workbench so that I can quickly and easily access anything I want.
Some ceramic artists mix their own formulas, or even have a clay manufacturer mix it for them. My studio is not big enough to warrant me doing that, however, I have occasionally mixed a couple of bodies together to see what happens.
It is also possible to gather your own raw clay and mix your own clay bodies. Raw clay comes from a variety of places, but can be readily found near springs, creeks or riverbeds. As a young child living in rural Georgia in the early 60s, I often played in and around mud puddles along the gullies and edges of the Georgia Red dirt roads. That dirt was very rich in clay. Making mud pies and even crude little pinch pots was possible, which provided endless hours of outdoor fun in the hot humid summers.
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| A few of my clay bodies, ready for use at the bench. |
I don't know why I didn't do this before, but I am starting a project to fire all my clays to maturity, unglazed (raw), as a means of reference. Here are just a few I started:
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| Just a few of my clay body samples. |
In Part II I will share with you the rest of my fired clay samples, and some samples showing how the same glaze will look differently on different clay bodies.
Meanwhile, here a few past samples of beads on a variety of clay bodies, each imparting it's influence on the glazes used with them.
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| Spiral Fossil Discs in a variety of clay bodies and glazes. |
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| Bead strands with beads in a variety of clay bodies and glazes. |
Here's totally random picture of Casey in my studio in Ulla's house (her crate where she likes to hang out - Shhh! Don't tell Ulla, she doesn't like Casey in her house)...
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| Casey in Da House! |
Stay tuned for Part 2 (in a couple of weeks) when I talk about how clay bodies affect glazes.
Karen Totten
Starry Road Studio
