Someone contacted me regarding problems she had with firing hollow beads, they were crumbling after firing. Here are some tips and processes for firing PMC3 metal clay coated cork beads.
- Form wood or cork clay into a shape. Attach it to a toothpick to use as a handle. It is best to place the toothpick in an area where you want a hole to be. If you are making a bead then place a toothpick on each end of the bead where you want the bead’s holes. The toothpick will be removed before firing, making a hole in the piece. This hole acts as a vent hole and a cleanout hole. The hole should be around 2mm in diameter.
- Make sure the wood or cork clay is completely dry before adding the metal clay. It will be completely hard when dry, no give.
- Smooth and shape form by sanding and filing. Using a rotary tool with sandpaper is fast and easy.
- Using lump clay: Roll your clay at 1mm thickness (4 cards), lightly wet the core form, and apply the clay. Seal the joins from inside with thick paste, cut the excess clay, and blend the seams with water and a clay shaper. Dry completely. Sand the seams to refine.
- Using clay slip: Measure the form with a millimeter gauge and write down the measurement. After coating the form the diameter of the bead should be 2mm larger. Paint approximately 8 coats of slip over the form. Allow each coat to dry completely between layers. To keep track of layers painted, place a mark on a sheet of paper before each coat.
- If using PMC3, slow ramp to 650F to slowly burn the cork. Hold at 650F for 30 minutes, then full ramp to 1290 for at least 10 minutes to 2 hours. Firing it at 1650˚ can risk the piece caving in. Ramping too fast can cause the piece to blow out making a huge crack.
- Support the piece with fiber blanket or vermiculite, but don't cover more than 50% of the piece. If using a fiber blanket, wrap the fiber blanket around it as to "embrace" it evenly on all sides and bottom.
- If the form is large, there is a chance of slumping. It's best to fire it upright and supported by fiber blanket or vermiculite up to the middle of the form’s height.
- After cooling, wash out the ashes. Insert a syringe tip and squirt with water. Leaving the ashes inside a hollow form can cause it to discolor.
Until next time, have fun claying around!
by Janet Alexander