Sunday, March 8, 2015

From the Ceramic Bead Maker's Studio, Part I: Clay & Clay Bodies

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.
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:
  1. 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. 
  2. 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.   
  3. ~ Clays and Clay Bodies by Linda Arbuckle.
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:
  1. 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.
  2. 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%.
  3. 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.)
  4. ~ 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.

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:

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.

Spiral Fossil Discs in a variety of clay bodies and glazes.

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)...

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

23 comments :

  1. Fascinating post Karen, I didn't know that the clays were deposited in different ways, I love to know how things came to be. Looking forward to the next instalment! (and your studio looks amazing, much more organised than mine!)

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  2. Very enlightening Karen - there's more to mud than meets the eye....

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  3. This is a great post! You are removing some of the mystery. Can't wait for the next installment.

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  4. Great post, gorgeous beads! I plan on referring back to this post one day. Since I had to replace my kiln recently I got one that will work with Clay which has been on my list for a long time.

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  5. Thanks Karen! It was a joy to read..your post is beautifully written & your beads are just amazing Karen, you are a gifted Artisan!

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  6. This was really interesting. As a geologist, I know where clay minerals come from, and I know about the transportation and deposition. But I didn't know how sediment deposits with lots of clay were transformed into clay that could be used by artists. And what does the term "plasticity" mean for the clay bodies? How does that term translate into the artists experience working with the clay?

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    1. Plasticity has to do with how workable or malleable the clay body is. If it is not plastic enough it will tend to crumble or crack. factors like particle size, water content, and amount of organic material contributed to the degree of plasticity. In terms of organic (microbial) material, as a clay body ages, it becomes more plastic due to continued growth of the organic content.

      Thank you for your comments. :)

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  7. Great post, thanks for sharing your knowledge. I know nothing about the clay in this sense and it's wonderful to be informed!

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  8. That was so interesting! I had no idea there was such a vast array of clay types! The picture of the 4 unglazed leaves is amazing to see, how they look so different from each other and what becomes possible. (Loving that your Casey slips into Ulla's bed, too..sounds like our house and my 3 doggie-kids!).

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  9. Very interesting post. Looking forward toast 2!

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  10. Thanks for sharing this info. Very detailed. <3
    Patty

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  11. Hey Karen, that is a very interesting piece on clay. I am hoping to get into making ceramic beads in the near future and it helps to know about the basic characteristics on the medium. I worked with clay for many years - a long time ago - so it is a bit like coming home for me. I did a workshop last year with Natalie Fletcher Jones of Peruzi (Australia) and loved it. I feature lots of her pieces in my work. To feature my own would be great. I will look forward to reading your next installment! Your beads, by the way, are gorgeous!!!!
    Glenda

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    1. Thank you Glenda - I hope you get back into clay. It's a lot of fun!

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  12. YOU are amazing. Thanks for the sneak peak into your organization... that is so impressive. With so many different bags open... would you care to share any secrets on how you keep it from drying out or do you just manage to get it used up fast enough??~

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    1. Hi Tracee, Thank you for your nice comment. I just make sure I keep the bag very well sealed up - tuck the flap under after I pull clay out of it to put into my mini-bins. I have had a few dry out over the years when I was careless about keeping the bag firmly sealed. In my little bins, I keep a moist sponge in with the clay (I put the clay on one side of the bin and the moist sponge over the other to keep it from contacting the clay and making the clay block overly wet on one side. I buy cheap cellulose sponges by the bag from the Dollar Store or wherever to use like this). Hope this helps!

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  13. OMG I need to try any clay named "Black Raven".

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  14. Fantastic post! I had no idea about clay bodies or that there are that many different types. Thanks for enlightening us!

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  15. How fascinating! I would love to see Part II of this. The second speckled clay sample is gorgeous! What kind is it? and do you use gas or electric kilns?

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  16. How fascinating! I would love to see Part II of this. The second speckled clay sample is gorgeous! What kind is it? and do you use gas or electric kilns?

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  17. Fascinating info! Thanks for sharing. I was hoping to find Part II but looks like you haven't posted it yet. I'm looking forward to seeing it. The second speckled sample is beautiful! What clay body is that and what type of kiln and firing do you use?

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