How to Make a Covered Clay Jar
Materials and Tools:
cone 10 stoneware clay body
calipers or ruler
50-cubic-foot propane-fired car kiln
porcelain decorating slip
trimming tool or piece of banding steel
Spanish red iron oxide
pieces of broken glass (optional)
decorating stamps (optional)
pastry wheel, toy truck tire or notched piece of spring steel
scratch glazes made from slip clays
silicone carbide or grinding wheel
1. Center an initial lump of clay (from 5 to 20 pounds, depending on the desired size of the finished pot) on the wheel and throw it into the form of the bottom half of the jar. Use ribs to refine the shape of the pot and smooth the throwing lines from the outside.
2. Set the piece aside to until it's leather-hard from top to bottom but not dry (the rim may sometimes need to be covered in plastic to keep it from drying too fast). The time required will vary from overnight to a couple of days, depending on the temperature and humidity.
3. When the base section has dried enough to support the weight of more clay, measure the rim with a pair of calipers or a ruler. Throw a ring of about the same amount of clay as the base (or a little less) to about the same diameter as the rim of the base. Form a gallery or groove in the rim of this ring, which should correspond exactly to the diameter of the rim of the base.
4. Remove the ring of clay from the wheel and put the base back on the wheel. After slightly wetting and scoring the rim of the base, invert the wet ring of clay directly onto the rim of the base section. Tap on the bottom of the bat to settle the wet ring of clay onto the rim of the base, and pass a cutoff wire between the bat and the base of the wet ring of clay and remove the bat.
5. With the wheel spinning slowly, seal the joint between the two sections of clay by working clay downward into the joint. Now the ring of clay can be thrown into the form of the top of the pot. As before, use a flexible steel rib to smooth and refine the form. Using a wooden knife, trim the base of the pot to the desired shape, undercut the foot slightly and pass a cutoff wire between the pot and the bat.
6. Measure the rim of the jar with calipers or a ruler and move the pot from the wheel to a moist place to dry slowly. On a new bat, center a pound or so of clay and throw a shallow bowl that will become the inverted form of the lid. The inside diameter should be just a touch larger than the outside diameter of the jar's rim. Pass a wire between the lid and the bat and set it aside to stiffen.
7. Once the lid is leather-hard, invert it onto the wheel and use a trimming tool or a piece of banding steel to trim it to the shape of a form you like. Score a ring in the center and attach a small piece of clay. Throw this clay into the form of a handle.
8. By this time, the jar should have dried somewhat and should be ready to be decorated. Start by coating the top half with a thick layer of porcelain slip. The top of the lid is usually coated with the same slip.
9. Decide how the jar should be decorated. Pieces of glass can be stuck into the clay that will run down the sides of the pot as it's fired. Stamps, seashells, dots of porcelain slip and rolled textures can be applied in patterns as desired. Roll a pattern onto the bottom half of the pot with a pastry wheel, a toy truck tire or a notched piece of spring steel. Remember that you'll be applying glaze to the pot later, so leave room for it to interact with your other decorations. When you're satisfied with what you've done, set the pot aside to dry. It will take anywhere from five days to two weeks to dry completely, depending on the weather and humidity. It will feel warm to the skin on the side of your face when it's dry,
10. When it's dry, sand off any rough edges and load it into a bisque kiln. Fire the jar to cone 04 with the lid in place.
11. Remove the jar from the kiln and dip the base in wax to prevent glaze from sticking to the bottom of the jar. Then glaze the pot as you wish. Coat the inside of the jar with a celadon glaze, dip the bottom half in an ash-base glaze and spray various glazes onto the top half of the jar with an air compressor and spray gun. Spray glazes especially thickly along the top so that they'll run down the sides of the pot.
12. Fire the pot in a 50-cubic-foot propane-fired car kiln. The firing usually lasts about 12 hours from the time the kiln is lighted until cone 10 is completely down. Once the kiln is shut down, allow it to cool for two days before opening. If bits of kiln shelf or kiln wash are stuck to the bottom of the pot, rub them off with a bit of silicon carbide from a kiln shelf or a piece of a grinding wheel.