BIG things with slabs.

Now that we all know how to roll out slabs of clay and assemble them so that they don't collapse (see SchoolArts, November 1992 issue, page 14), let's try to make bigger projects.

Once again, it is important that sketches be made first in order to fully understand the scope of the sculpture to be built. Be sure to include dimensions. Sometimes it's helpful to make separate sketches of any technical details. The example below shows a detailed section of how parts of a sculpture will be built so that they will fit together after firing.

Preparing the Clay

Although most clays can be used to construct large-scale ceramic works, problems can occur. Pieces can become very heavy, or the work can dry unevenly and warp or crack. The best way to minimize these situations is to add organic materials to the clay before rolling the slabs.

Some clayworkers mix grass clippings or rice hulls into the clay. Others use coffee grounds for the delightful aroma during firing. Medium to coarse-grained sawdust is probably the best material to add to the clay, and the easiest to obtain.

The sawdust increases the wet strength of the clay (the ability of the clay to stay together during construction). The sawdust also reduces shrinkage and warping while the clay dries. When the finished work is fired, the sawdust burns out, making the sculpture lighter in weight.

Adding ten to twenty percent of the sawdust by weight will go a long way toward preventing problems. Grog (ground-up fired clay) can be used in place of sawdust to help reduce potential warping and cracking problems, but it does not burn out and can therefore add weight to the finished work. The addition of chopped nylon fiber or chopped fiberglass strands can achieve similar results, but I don't recommend these materials for classroom use.

A simple way to add the sawdust to the clay is to slice thin sheets of clay and sprinkle handfuls of dampened sawdust onto them. Stack the slices together, knead them well and repeat the process until all the sawdust has been mixed in. Of course, a clay mixer will simplify the job. Store the clay in sealed plastic bags for at least one week.

Getting It Done

The concept is clear, the sketches are done, the clay is ready. Now all you have to do is build the object.

The only real difference between constructing a large slab work and a small one is care. Kneading and rolling the clay proceeds in the same manner. Large slabs can be somewhat thicker, however, and therefore should be allowed to stiffen more slowly before use. Joining procedures are also the same. After joining, allow the work to dry more slowly than you would a smaller work.

Complicated braces or interior armatures are not really necessary. To avoid sagging or slumping, it may be best to construct the work on its side, or even upside-down. Allow the piece to dry in the same position and, if possible, fire it that way too. if the work is complex or spindly with points touching the ground like an animal's legs, it's a good idea to use a shrinking slab with the same clay, and place the object on top of it. The slab will dry and shrink at the same rate as the sculpture, and will protect the base of the work from becoming distorted. For best results, fire the work on the shrinking slab.

Wall Works

A classic classroom project has long been the ceramic mural. All too often, this consists of merely painting overglaze onto commercial tiles. While this can be colorful and fun, it misses the major point of doing a mural in clay-depth. Visually effective ceramic murals are those that are executed in high relief. Not only do they make images appear more realistic, but the murals have a tactile quality as well. And they're not that difficult to make.

Whether the image is to be abstract or representational, the process is the same--sketches first. For obvious reasons, it is assumed that the space where the completed mural is to be installed has been approved. Take measurements of the area, note any surface irregularities, and spot any electrical fixtures, vents or other protrusions that need to be taken into consideration. Make as many small idea drawings as are necessary until the final imagery has crystallized.

After all aesthetic decisions have been made, it is time to make the master drawing. This picture will later be transferred to the clay, so draw it large enough to take the final shrinkage of the clay into consideration. In other words, if your clay shrinks ten percent, make the drawing ten percent larger than you need the fired work to be.

Ideally, clay for the mural should be spread out in one sheet. If there is not enough space to do so, lay out workable sections, and note them accurately on the master drawing so that everything will fit together later.

In either case, prepare the working surface (table or floor) by spreading canvas over the area. The canvas will protect the floor, and help to keep the clay moist during the early stages of construction. Slam fistfuls of clay onto the canvas. Bat the clay with a large wooden paddle or mallet to beat out air pockets. Work the clay with a rolling pin to be sure the surface is level.

Trace the drawing onto the clay and start modeling. Carve or build up the surface to achieve the desired look. While modeling one area of the mural, keep the others covered with plastic to prevent drying. Mist the entire surface with water occasionally to keep the clay workable.

When the mural is fully modeled, allow the clay to stiffen somewhat. Cut the mural into manageable sections. Do the cutting along lines that enhance the forms where possible.

Finishing Up

Hollow each piece of the mural to a thickness of about 3/8". This will allow the work to dry evenly, and also make the finished work considerably less heavy. Leave a rim on the underside of each piece at least 1" wide to provide surface area for adhesive.

Use your normal firing and finishing methods to complete the mural. If the work is large or complex, it's a good idea to number each piece on the back with underglaze, and draw an arrow pointing up.

Installation

For safety and liability reasons, professional masons should be employed if the mural is to be permanently installed. For semi-permanent installation, use 3/5" plywood to prevent bending. Roughen the surface of the wood for better adhesion. Of all the adhesives currently available, GE Silicone Sealer II gives best results. Follow the precautions on the label. With a caulking gun, apply a bead of the sealer over the back of a tile. Press the piece in place with a twisting motion. Repeat until all the pieces are in place.

Allow the silicone to set up for several days before bolting the plywood to the wall.

Now stand back and admire your work!