How to Make Porcelain Knit Cups
Creating the Mold
- 1). Choose a glass the size you want your finished mug to be.
- 2). Find a sweater with a design that pleases you with a sleeve diameter that will fit snugly over your chosen glass.
- 3). Cut the sleeve so that it covers the exterior of the glass. Glue it in place.
- 4). Paint the sweater and glass inside and out with two thin coats of orange shellac. After 15 minutes, dust with baby powder.
- 5). Lay a 1-inch thick base of clay on your work board. Place the glass on top and build around the sweater; don't press the clay into the knit or it will be difficult to remove. Build the clay out at least one inch from the cup and up to within one inch of the top of the glass. At this point, you'll want the clay to adhere to the knit so that it forms a bond that will prevent plaster from seeping past.
- 6). Allow the clay to dry to the leather hard stage. It will be smooth and mostly dry, but still retain a bit of flexibility. Cut excess clay away from the glass, squaring it off, being careful to leave an inch of clay around the glass at all points.
- 7). Cover the inside of the cup, the top of the clay, the visible exterior of the cup, and the inside of the casting boards with mold soap.
- 8). Screw the metal brackets on one of the exterior edges of each casting board. Place the boards around the clay form. One edge of each casting board will extend past the perpendicular joint where it meets the next casting board; tighten C clamps to hold the wooden extension against the metal bracket.
- 9). Seal the edges of the clay against the casting boards with your finger or the back of a spoon.
Mix enough plaster of Paris to fill the glass and cover the top by one inch. This amount will depend on the size of your glass and how widely-spaced your casting boards are.
Pour the plaster into the glass and on top of the mold until the top of the glass is covered by at least one inch.
Allow the plaster to dry for at least 24 hours. Remove the casting boards and use the file to smooth the edges of the plaster.
Twist the clay base off the work board and invert so that the plaster is on bottom. Pull the clay away from the plaster. The glass will remain in the plaster. If there's any clay remaining on the plaster or the sweater, clean it off. Wipe away any orange shellac that's transferred to the plaster with alcohol.
Use a coin to twist divots out of the plaster in at least two places. This will provide a way for you to line up your mold correctly when you pour the porcelain.
Check the sweater to insure that it's still covered with a layer of orange shellac. Make sure you get in all the nooks and crannies so that the knitted design shows up clearly. Dust the surface with baby powder.
Cover the model, the plaster surface, and the casting boards with mold soap.
Place the casting boards around the form and clamp them together as before.
Mix enough plaster of Paris to cover the glass with an inch of plaster. Pour the prepared plaster into the mold around the glass. Allow the plaster to set, then remove the boards and smooth the edges with the file.
Turn the mold on its side so you can see the line of mold soap between the first and second pours. Gently insert a flathead screwdriver into the line and tap lightly with a hammer. When the mold loosens, turn and repeat on another side. Continue until all four sides have been loosened.
Pull the loosened halves of the mold apart very carefully. Remove the glass, being careful not to chip the plaster of the mold. If you glued the sweater to the glass only lightly, you may be able to remove the glass itself, then pull the sweater inward, away from the plaster, to remove it.
Carve out a pour hole and use the file to smooth the edges. Let the mold dry completely before using.
Making the Cup
- 1). Place the dry halves of the mold together, fitting the bumps of the one side into the divots in the other side and rubber band the mold firmly together.
- 2). Stir the porcelain slip before using to evenly distribute all particles. Pour the slip into the mold down one of the walls until the mold just overflows.
- 3). Watch the overflow of slip at the pour hole. If it starts to sink, add more slip. Continue adding slip until the overflow remains rounded. This is when you'll know that your mold is fully filled.
- 4). Allow the porcelain to dry overnight. Remove the rubber bands and separate the halves of the mold. Use the file to carefully grind off the stem from the pour spout.
- 5). Fire your dried cup in a kiln. You can use your own or you can take your cup to a nearby college, high school, or paint-your-own pottery shop and ask them to fire it. They may charge a fee for this service.
- 6). Glaze the fired cup. You may do this in your own studio if you have one, or use the facilities at a college, high school, or paint-your-own pottery shop.