This week I decide to post some more steps on how to make and then fire the hollow forms.
*To repair a hole:
Cork clay and wood clay are moldable substances that burn away during the firing process and allow you to easily make hollow objects. Cork clay and wood clay are easily molded in to any shape and makes an excellent internal structure (core) for metal clay.
Working with cork clay and wood clay
1. Only remove the amount of cork clay or wood clay needed for your project. Tightly wrap the opened package so that it is air tight.
2. Using your fingers or a form, mold the clay into a shape.
TIP: Embed a toothpick into the cork clay to use as a handle while covering it with metal clay. *If the toothpick creates a hole in your finished metal piece, then fill the hole after firing.
3. Allow the clay to dry completely (overnight or 24 hours).
4. Fill in any cracks by applying water to the area and then spackle fresh cork clay into the crack.
5. When completely dry, sand the surface smooth, and if wanted file any design into it.
6. Cover the core shape with metal clay.
If you are applying slip:
a. Measure the core’s width with a millimeter gauge.
b. Write down the measurement.
c. Apply at least 10 coats of slip allowing it to dry between layers.
d. When the piece measures 2mm thicker than the starting measurement, the metal clay is thick enough.
e. Dry completely
f. Sand metal clay and apply any designs using metal clay paper or syringe clay.
If you are applying lump clay:
a. Roll the lump clay 4 cards thick.
b. Lightly wet the core form.
c. Wrap the clay around the cork clay form blending the seams with a clay shaper, and cutting off excess clay.
TIP: it’s good to have a small hole to vent the fumes from the cork or wood clay. The hole can be filled in a later firing. (See “To repair a hole.”)
d. Dry completely.
e. Sand clay and apply any designs using metal clay paper or syringe clay. You can also file designs into the piece.
If you are applying syringe clay:
a. Apply several layers of syringe clay over the cork clay.
b. Decide how the piece will hang and make sure there is plenty of syringe clay at the place(s) it will hang from. Otherwise, after firing this area will be weak.
c. Check all syringe connections for good contact. Blend them together with a blending stick, making them solid.
d. Look for large gaps and fill in with syringe.
e. Dry completely.
7. Remove the toothpick if you used one. Sometimes the toothpick won’t pull out. Cut it off and allow the stump to burn off in the kiln.
*To repair a hole:
a. Using a mixture of Lavender oil and PMC3 paste (4 drops of oil to the paste container) paint a coating of paste in and around the hole. Paint some paste on the inside of the piece if able. Apply PMC3 lump clay into the hole using a clay shaper. (Anywhere the fresh clay is to be applied, paint a coating of oil paste.)
b. Allow to dry.
c. If needed, apply a second coat of lump clay.
d. Sand and blend in with fired piece.
e. Dry completely.
f. Fire in kiln with the piece supported on fiber blanket or in vermiculite at 1290˚F for 10 minutes.
Firing metal clay with cork or wood clay
· Metal clay over cork or wood clay must be fired in a kiln.
· The kiln temperature must be ramped up so that the cork/wood has time to burn out before sintering the clay. Set the first ramp at 650 degrees for 30 minutes and the second ramp at FULL to the required sintering time for the metal clay used.
· If the cork or wood contains moisture at the time of firing, it will cause a hole in the metal clay by turning the moisture to steam and the steam escaping from the sealed clay.
· Fire the kiln in a well ventilated room, cork or wood clay creates smoke as it burns.
· Do not open the kiln door during burnout; this will cause a fire in the kiln.
· Place the piece on a support so that it doesn’t lose its shape during firing. Use a bowl with vermiculite or place it on a fiber blanket. If the piece is very large there is a risk of it slumping. It’s best to fire it upright and supported by fiber blanket or vermiculite up to its center.
· After firing, clean the ash off the metal by washing with water.
· Finish piece by using a brass brush with water or tumbling in steel shot.