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December 2, 2009

How to Make Agateware Vessels on the Pottery Wheel

by Michelle Erickson and Robert Hunter Read Comments (15)

Agateware is a type of pottery that is made from a prepared mixture of various colored clays and mimics the variegated appearance of agate stone. It originated in the late seventeenth century in England, and is one of many great techniques that utilize colored clays to create interesting surface features. There are two types of agateware, one is wheel thrown and the other is made using handbuilding techniques, and is classified as laid agateware.

In today’s post, an excerpt from the January/February 2010 issue of Pottery Making Illustrated, Michelle Erickson and Robert Hunter explain the important considerations potters need to make when making agateware and demonstrate throwing agateware on the pottery wheel. An article on the handbuilt version of this technique was included in the November/December 2009 issue of PMI. - Jennifer Harnetty, editor.

Background
The earliest English thrown agate is found among the products of John Dwight (even though he himself referred to it as marbled). Considered by many as the father of English pottery, Dwight is well known in the annals of ceramic history for his innovations. He conducted numerous ceramic experiments beginning in the 1670s, delved into the mysteries of porcelain, and recorded his recipe to produce “marbled” stoneware.

Dwight’s notes reveal two important material considerations in making an agate body: clay color and clay compatibility. To create the illusion of agate striations, different color clays must be obtained naturally or by modification, adding pigments or coloring agents. The tone of a natural clay can also be altered by sieving to remove impurities such as iron and sand.

Creating a successful variegated appearance also depends on the proportions of clay colors used. Clues for understanding problems related to combining multiple clays are also contained in Dwight’s formula. These include shrinkage rates, firing temperatures, density, plasticity, elasticity, and strength. All of these properties must be considered when mixing dissimilar clay bodies.

For more ideas for the pottery wheel, be sure to download your copy of Three Great Pottery Wheel Throwing Techniques: Tips on Throwing Complex Pottery Forms Using Basic Throwing Skills, which is free to Ceramic Arts Daily subscribers.
The Wheel-thrown Agateware Process
To begin, clay slabs are built up, alternating the colors. This stack is then wedged or folded to form a ball that can then be thrown on the wheel.To begin, clay slabs are built up, alternating the colors. This stack is then wedged or folded to form a ball that can then be thrown on the wheel.
Care has to be taken during wedging to ensure the clays are mixed without overly distorting or blurring the resultant agate pattern. For demonstration purposes, the wedged ball is cut to show the pattern prior to throwing Care has to be taken during wedging to ensure the clays are mixed without overly distorting or blurring the resultant agate pattern. For demonstration purposes, the wedged ball is cut to show the pattern prior to throwin. The degree of success in an agate pattern comes from the initial wedging process as well as the throwing. 
During throwing, the surface of the clay body becomes smeared so that agate patterning is obscured.The prepared clay ball is then centered on the wheel. Once centered, the clay ball is opened and pulled quickly into a cylinder. During throwing, the surface of the clay body becomes smeared so that agate patterning is obscured.
Care has to be exercised during throwing so as not to overwork the clay; otherwise, the pattern becomes muddled. This test piece was cut in half to show how the agate patterning shifts in the cross section of the clay wall. The different colors should remain distinct.Care has to be exercised during throwing so as not to overwork the clay; otherwise, the pattern becomes muddled. This test piece was cut in half to show how the agate patterning shifts in the cross section of the clay wall. The different colors should remain distinct.
Since nearly all Staffordshire thrown agate was subsequently trimmed on the lathe, the veining usually appears sharp and crisp. Later smearing and smudging can occur at the attachment points of handles or spouts as evidenced on some antiques. Most potters don't have a lathe, but the pattern can be revealed by using a metal ribSince nearly all Staffordshire thrown agate was subsequently trimmed on the lathe, the veining usually appears sharp and crisp. Later smearing and smudging can occur at the attachment points of handles or spouts as evidenced on some antiques. Most potters don’t have a lathe, but the pattern can be revealed by using a metal rib to scrape away the slip and outer layer of clay from the surface.
Using a shaped rib or the metal rib again defines the foot or base while maintaining a crisp pattern. Using a shaped rib or the metal rib again defines the foot or base while maintaining a crisp pattern.
Lastly, scraping the interior of the form with a metal rib reveals the agate pattern on the inside.Lastly, scraping the interior of the form with a metal rib reveals the agate pattern on the inside.

 

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15 Comments

  1. Michael | December 2nd, 2009 at 10:38 am

    Great Post! I’ve done a lot of swirl but haven’t tried the agate ware! Bruce Gohlson does some nice agate!

  2. surendera | December 2nd, 2009 at 11:05 am

    Its a great idea to mix and agate. Every post at your portal teach us so much.

  3. Ann | December 2nd, 2009 at 11:14 am

    Catawba potters here in NC do some lovely agate ware. Thanks for the instruction.

  4. Kevin | December 2nd, 2009 at 12:16 pm

    Clay compatibility cannot be stressed enough when making agateware. There’s nothing like making a number of pieces using the process outlined above, trimmed and with handles applied, only to have them crack or flake apart during firing due to shrink rate differentiation.

    I also count my strokes during wedging in order to ensure consistency in marbling between pieces. Keep in mind, mixing occurs during centering and pulling, so you’ll want to go very easy on the wedging. That’s why it’s critical that care is taken to avoid trapped air when initially layering the clay. Marbling consistency between pieces is also affected by the rate at which each pot is pulled into cylinder. A quicker pull gives you a more dramatic effect.

  5. Cindy | December 2nd, 2009 at 1:14 pm

    Kevin, it would be nice to start experimenting where you left off. So about how many times do you wedge, and are you wire wedging or kneading?

    Thanks!

  6. Michelle | December 2nd, 2009 at 1:14 pm

    Thank you for this post. I make agateware and was thrilled to see that this technique has been getting some focus. You can see an example of my thrown agateware on http://michellejunkinceramics.blogspot.com/ and you can see more pictures where I sell it on Etsy.
    Some things I learned along the way is to let the thrown agateware clay dry very, very slowly in the damp box. Testing on the clay bodies to find capatibility, as mentioned in other posts on this page, is key. Also when I make my clay balls for the wheel. I wedge the white clay separate from my black clay. Then I take a wire and cut each ball into 4 pieces; like a big apple slices. I take two black slices/pieces and two white slices/pieces and then assemble them together (slam them together) into a ball. Looking down at the completed ball, it has a distinct color pattern alternating 1 white slice, 1 black slice, 1 white slice, 1 black slice around the ball. Repeat process with other pieces…thus now you have two balls ready to throw. (Play around with how you assemble the balls, change up how many pieces of each color, you add. Try a ball that is half white, then half black.) When trimming a foot, make it wider than normal…so that cracking does not occur when the two clays dry or when fired. Also test and play around with glazing. I found that combinations of underglazes with my regular glazes help cover the dark clay or the white clay from showing through when I want complete color coverage.)

  7. Dawn | December 2nd, 2009 at 1:40 pm

    Can I just add my own oxides to the clay to create a white and … say irong oxide? I would think this would not change the shrinkage too terribly much since I start with the same basic clay body and I have done this with laid agateware. I am a teacher at a high school with a low budget and am curious to know if this is something worth trying with my more advanced students.

  8. Michelle | December 2nd, 2009 at 2:20 pm

    Hey Dawn, I don’t see why you couldn’t make your own colored clays. Maybe you could have your students experiment with Mason Stains. I realize this might not fit your budget, but it might be worth a try.
    Add Mason Stains by weight as a percentage of dry ingredients when mixing your own clay. When coloring moist clay, allow for 30% water, then add Mason Stains as a percentage of dry ingredients’ weight (ie,
    17½ pounds dry out of 25lbs total weight).
    Greens, Blues & Blacks: 2 - 5%
    Yellows, Pinks & Purples: 5 - 10%
    (the above recipes on how to use Mason Stains was found at http://www.georgies.com/pdfs/mason-stains.pdf )

  9. Michael | December 2nd, 2009 at 3:15 pm

    An excellent book about coloured clay is Paulus Berhenson’s “Finding One’s Way With Clay.” This should be a part of everyone’s clay library, whether you’re interested in agate ware or not.

  10. Kevin | December 2nd, 2009 at 6:21 pm

    Cindy, similar to Michelle, I knead the clays separately, wire-wedge them together, albeit in layers, and then I finish with no more than 10 half-hearted kneads. It’s a bit of a balancing act; not enough kneading, and the clays can be prone to separating or cracking during firing. Too much kneading, and the piece will end up muddled. And as I mentioned before, you have to take into consideration mixing that occurs during the centering process. Working efficiently on the wheel is important. Take notes and have fun!

    Michelle, very nice work. I’ll try your apple-slice idea next time.

  11. Leonor | December 2nd, 2009 at 6:30 pm

    Amo este trabalho. Acho-o maravilhoso.

    Excelentes explicações de Michelle Erickson e

    Robert Hunter.

    Leonor

  12. Oliver | December 3rd, 2009 at 1:46 pm

    I use two pieces of clay, no wedging, and throw fast - dramatic swirl: http://www.etsy.com/view_transaction.php?transaction_id=16314252. Like the demo!

  13. NARCISO | December 4th, 2009 at 9:02 pm

    UNO DE LOS MOMENTOS MAS INTEREZANTES DE MI CARRERA COMO CERAMISTA ES HABER ENCONTRADO LA TECNICA DEL MARMOLEADO, ES SIMPLE PERO AL MISMO TIEMPO COMPLEJA Y CON MILES DE PROPUESTAS APLICABLES EN BAJA,MEDIA Y ALTA TEMPERATURA.
    ME ENCANTA.

  14. Bevy | December 8th, 2009 at 12:49 am

    Dawn, it would be much less expensive and easier to just use two contrasting clays that shrink at the same rate. We use both a white clay and a red clay in our studio for various projects, which includes joining the two for marbled clay (AKA agateware.) That way, we don’t have to make a colored clay. I have also used Ravenblack Clay from KPS for the same thing along with other prepared clays.

  15. Michele | July 25th, 2010 at 10:22 pm

    i was talking with my clay/glaze supplier about a new glaze they made, he told me it worked best on red clay but knew i used white clay. I gave me a bag of iron oxide and told me to create a slip with it to put on the outside of my pots when i am done making them (basically fool the glaze) anyone done this? if so, couldn’t you add iron oxide to your current white clay supply to complete the agate projects? i haven’t made the red slip yet,but am curious to try it

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