Published Jul 27, 2009
In any vapor-firing process, such as wood, salt, or soda, wadding (small balls or rolls of a refractory clay mixture) is a must to keep surfaces from sticking together. Most potters mix up a batch of wadding, roll up little balls of the stuff, and stick 'em to the bottoms of their pots with spit or water as they are loading the kiln. But sometimes, as pots are repositioned in the kiln, wadding can fall off with this method, slowing down the kiln-loading process.
Today, University of Alabama graduate student Jason Doblin explains the method the UA ceramics department has come up with to make wadding pots foolproof. - Jennifer Poellot Harnetty, editor.
Anyone who fires regularly in a wood, soda, or salt kiln has to deal with the ever-present concern of wadding the bottoms of their pieces. Although the principle of wadding work is not complicated, the process can vary drastically among potters. Here's the scenario, you have a bucket of wadding material handy as you begin to load your kiln. With each piece you form three balls, spit on them, and adhere them to the bottom of each pot. Next, you place each pot where you believe it will live in the kiln for the duration of the firing. What also inevitably happens is that you need to reposition a piece in the kiln because of another piece that would work better in its place. As you pick up the pot the wadding falls off, and the expletives begin.
During my current graduate studies at the University of Alabama, we have started to employ a new method for wadding work that speeds up prep time and removes many of the headaches associated with having to reposition wadded work in the stacking process. What follows is what we do differently at the University of Alabama and what could possibly turn wadding ceramic work into a joy...okay, at least not a pain.
Begin by filling the bottom third of a small bucket with 2800 grams (or approximately 6 pounds) of clay slop from your slop bucket.
Weigh out 200 grams of alumina hydrate and pour this into your clay slop. Fill up a second small bucket with very fine sawdust (use nothing coarser that what would fall through a 20 mesh screen).
Introduce the sawdust to the slop and alumina hydrate a handful at a time, continue blending the mixture until the consistency becomes like a workable clay consistency.
Proceed to wedge this mixture until it is fully blended.
Break the clay up into manageable sizes to roll out slabs. I prefer to use boards and a rolling pin to do this step, but a slab roller would be a fine choice if available. The clay should be rolled out to 3/8 inch thick (a thicker slab would be desirable for making wadding for large and/or heavy pieces).
After the slab has been rolled out on a canvas mat, lay another canvas mat on top of it. Placing a hand on both sides of the slab, flip the slab over. This will cause the clay to release off of the canvas that it had previously been rolled out on. Trim off any cracked edges. Place a translucent plastic sheet over the slab.
Impress vertical grooves into the clay, with a pizza cutter and a straight edge.
After vertical lines have been impressed, proceed with impressing horizontal lines to create a grid.
Remove the plastic sheet and allow the slab to dry.
Break the slab into manageable sections and bisque fire. The individual pieces created by the grooves in the sections may now be broken off (in much the same way as two pyrometric cones are separated). Use a hot glue gun to adhere the bisqued square wads to the bottom of each piece.
The glue will hold the wads in position through the stacking process, but will burn off during the firing. After firing, the wads can be knocked off the piece the same way conventional wadding is removed.
Have questions about soda firing? Find out more in Gail Nichols' well-researched book Soda, Clay and Fire.