How to Make a Ceramic Cactus Vase
Materials and Tools:
No. 1 pottery plaster
small plastic spatula
cone 6 clay
small board or bat (for plaster work)
1. Fill a gelatin mold with about 5 pounds of clay and turn it upside down to anchor it on small board.
2. Fill in undercuts at the bottom of the gelatin mold with small coils of clay. Remove excess clay around the mold with a small spatula.
3. Cut thick slabs of clay with a wire tool at least 1 inch taller than the gelatin mold.
5. Roll out extra coils of clay to reinforce the outside bottom of the clay wall.
6. Spray the gelatin mold and interior clay walls with cooking oil to act as a release agent for the plaster. Smooth the oil with a paintbrush.
8. Pour the plaster on top of the gelatin mold until the plaster is an inch thick on top of the mold.
9. Gently tap the plaster mold to aid in the removal of air bubbles.
10. When the plaster has set (usually 30 to 45 minutes in dry weather), remove the clay walls and turn the plaster upside down.
12. Cut several 3/8-inch slabs of clay from a larger clay block with a wire tool and hardboard shims for even consistency.
13. Press the slabs inside the plaster mold in a patchwork fashion, using a sponge at first and being careful not to rip the clay. Blend the clay seams thoroughly with fingers. Roll a coil of clay and press it on the inside top edge to reinforce the seam. Let the clay dry to a leather hard stage.
15. Repeat steps 13 to 15 to create another half. You'll have one for the top and one for the bottom.
16. Attach the halves by scoring with a needle tool and slipping with watered-down clay at the middle seam. Add small coils of clay in any grooves as necessary.
17. Center the ceramic vase on the potter's wheel and secure it with three coils of clay around the base.
19. Add coils of clay and blend them together to throw the neck of the ceramic cactus vase.
20. Add clay slip to a sandwich-size plastic bag, knead for consistency, snip off a bottom corner with scissors and extrude small cactus-like spikes onto the form - similar to applying icing to a cake with a pastry bag.
21. Once bone-dry (about 24 hours later), bisque-fire the vase in the electric kiln to 1,700 degrees F. The vase is "soaked" overnight at 200 degrees F and then slowly fired to temperature in about 6 to 8 hours. It will take about 24 hours to cool to room temperature.
22. Glaze the by first pouring glaze on the inside with a plastic cup, fully coating the interior surface. (The glaze contains 4 percent copper carbonate and 6 percent rutile for interesting color effects).
23. Submerge the main body of the vase in glaze up to its neck.
24. Once dry (after a minute or two) turn the ceramic vase upside down and glaze the neck by submersion as well. Remove the glaze on the bottom of the vase with a sponge and allow to dry fully.
25. Glaze-fire to cone 6 in the electric kiln, which is about 2,200 degrees F. To grow rutile crystals, the vase needs to be cooled more slowly than normal. This means turning the kiln back on "medium" at periodic intervals during the cooling process.