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Mark Gordon used a specialty mortar to attach bone-dry pieces together to form this sculpture.
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August 25, 2008
Pushing the Envelope: Creating Complex Ceramic Sculpture with Bone-Dry Clay and a Simple Mortar
by Mark Gordon | Read Comments (1)
One of the challenges of working with clay is timing, especially when constructing a complex sculptural form. Making sure that all components are at the appropriate moisture and stiffness level when joining pieces is one of the key considerations that sculptors must address. Sculptor Mark Gordon has adapted a technique he first observed being practiced by traditional Egyptian brick makers for his ceramic sculpture. The technique is a sure-fire and simple way to securely attach bone-dry greenware to bone-dry greenware. It works great for him, especially when he is under pressure to meet deadlines and scheduling challenges. Mark shares his technique with us today. - Jennifer Harnetty, editor.Here's a method of joining dry clay to dry clay for use in sculptural work. For simplicity's sake, and to promote an even shrinkage rate and firing contraction, I use a slop-consistency mortar mix made from
slaked scraps of the same clay body that the sculptural parts are made from for joining, bonding and surface coating. To create contrasts in color between the mortar and the clay, I often add a darkening oxide or colorant such as iron oxide, manganese dioxide or black Mason stain.
Mixing the Mortar Clay 
To make the mortar for assembling dry greenware, begin by mixing slaked scrap clay with powdered clay and aggregate material. The sculpture and the scrap should be made from a stoneware body. The fire clay in stoneware helps to make the structure stronger, and using a high-temperature clay body extends the glazing possibilities later. The aggregate material is the key feature of this mortar. I use large quantities of non-plastic material such as mixed-sized sawdust or
perlite, in a ratio of two parts aggregate to one part wet clay.
First, mix the clay slurry, adding water if needed until it reaches a consistency about midway between slip and plastic clay. Use a drill mixer or clay mixer for larger quantities, and a mortar trough (available at hardware stores) for smaller batches. If you plan to build large-scale forms, add a small handful of shredded nylon fiber to about 60 pounds of this wet mix to improve the clay body's dry strength. Next, mix in the aggregate. Sawdust is my principal aggregate, as it is inexpensive and readily available. I add small quantities of perlite for its rough tooth, texture and toughness. Note: vermiculite (expanded mica used for gardening) should be avoided, because the clay may pit or flake after firing.
The final mortar mix is a stiff slop, similar to what I saw used by Moroccan artisan brick-makers. Though not as wet as slip, it is still far too wet to wedge. Due to the predominance of absorptive non-plastics, even slight aging causes the mortar clay to stiffen quickly. Despite this fact, you can leave the mixed clay out in the open air because the dried outer crust can easily be remixed or slaked in just moments. This clay is not fussy!
JoiningJoining pieces with this mortar works best when the parts are bone dry. The process works because the mortar has several specific qualities that help lock the parts together:
• Rough clay provides many nooks and crannies that act as tiny, locking undercuts.
• Nylon fibers in the mixture provide a Velcro-like effect.
• The wet clay in the mortar causes the dry clay in the separate components to absorb water and slake around the edges.
• Large amounts of aggregate minimize wet-to-dry shrinkage.
To work with the mortar, dip a piece into the mixture (figure 1), then firmly press the piece onto the main structure (figure 2). Smooth out the joins and compress the mortar slip into the seams (figure 3). For a more integrated appearance, paint a layer of mortar slip on all component parts (figure 4). After firing at any temperature, this mixture remains mechanically porous. The bonds between the sections rely on interlocking construction - a sort of "silico-organic" mortise and tenon, with the mortar locking into recesses within the forms.
To learn how Mark Gordon glazes and then pit and saggar fires his work, check out this article in its entirety on the Pottery Making Illustrated website.
Mark Gordon teaches ceramics at Barton College in Wilson, North Carolina. To see more of Mark's work visit his website at www.markgordon.com. Photos by Ron Sowers, Steven Steward and Max Gordon. Not sure about a term you see here?
You can find definitions and explanations for more than 500 ceramic terms, from agateware to zirconium,
in the Ceramic Arts Daily Glossary. |