Hollow Cast Info

Why cast it hollow? your piece will actually be stronger because it will reinforced with burlap. We will use less plaster making the work lighter and easier to move which is a big benefit. Since the work is hollow, you can consider different options for mounting your finished piece.

You will need:

Pliers
1" metal putty knife
3 clean chip brushes
Murphy's oil Soap only!
Mineral Oil USP Lubricant/ Laxative (from the pharmacy)
Burlap cut into 1-1/2" x 1" several squares (Home Depot garden section)
Plaster
Two small buckets- 1 for water, 1 for plaster.

1. Soak your mold until the seem appears, and then opened it up. If it will not come apart after you see the seem clearly, jam a hammer handle down into the wet clay to displace the contents of the mold. This should put pressure on the walls and help the mold to open with out damaging your work.

2. Remove the armature and clay inside. clean the armature. Recycle the clay when possible by picking out plaster and re-hydrating it.

3. Pull out toothpicks with pliers. Clean mold thoroughly. Remove all clay residue by gently scrubbing with a soft toothbrush and mild soap. Pick out any small areas clogged with clay.

Remember: If you see that there were air bubbles in the mold,(or the negative) these will translate as warts or bumps on the cast, (or the positive). These will be easy to sand off, so don't worry.

4.Dress the edges- Meaning gently scrape the mold lines with the edge of your putty knife to create clean corners where the shims were. This will prevent gaps in the seems on the positive. (See demo).

5. If your mold is dry and not cold and clammy to the touch, soak it for 10 to 15 minutes.

6. Use a dry chip brush to coat the inside of both sides of the mold with Murphy's Oil Soap. Cover all areas including the ledge where the shims were. Keep a paper towel on hand to wipe bubbles and debris off your brush. Remember to avoid making foam on the surface. Do not let the soap pool up. If you get pools in the low points, pick up extra soap and distribute it elsewhere. The result should be a waxy, shiny surface.

7. Brush on a layer of mineral oil over the soap. If an emulsion starts to form dab it out with a brush. Wait a minute to see if the oil absorbs or pools. If it absorbs, ad a little more. If it pools, dab with brush to remove excess. You should start to see a high shine in the mold. For very detailed or tight areas, you may want to put in a thin layer of Vaseline for extra release power.

Remember: Make sure you put soap and oil on the shim wall. This will make it easy to remove any plaster that gets on there accidentally.

8. Make a small batch of plaster. When it is about the consistency of pancake batter, dab it on the prepared surface with a new chip brush. Come right up to the edges of the mold but not over onto the shim wall. Let plaster settle in low points, like the nose, but do not fill these areas all the way with plaster. (Why? Because we want these sensitive areas to be reinforced with burlap). The result should be a consistent layer of plaster that is 1/8" - 1/4" thick.

9. make a very thin batch of plaster, it should be about as thick as heavy cream. Take your burlap squares and dip them into water, then into plaster. Starting in the middle and working you way out, press burlap patches into the mold, Over lap them so that each point is two layers thick. Avoid bunching and air bubbles by smoothing each patch with your fingers. For small tight areas, do not blanket with one big patch, used smaller pieces that overlap. (See demo).

10. when both sides of the mold are covered with the burlap patches, trim any fibers that may extend over the top of the mold. clean the shim wall so there are no plaster drips on either side of the mold.

11. Put the mold back together with the most stable side down. This usually means the back. It should fit perfectly. If it does not, check for obstructions on the shim walls.

12. Make a small batch of plaster. Make just 2 or 3 burlap plaster patches and place them on the seem of the mold to hold it together. When plaster starts to thicken, trowel 1/4" over the entire seem with your putty knife to completely seal your mold.

13. Make another small batch of plaster. Take additional burlap squares, dip in water, then thin plaster. Stick your arm in the mold and place patches as best you can along the interior seem of the mold. If your can not get all the way to the top of the head, that is okay.

14. Make a final batch of plaster it should be about 1/4- 1/2 the volume of your sculpture. This can range from 1 quart to 1/2 gallon. The plaster should be the consistency of pancake batter. Pour the plaster into the mold and roll it around so that the seems and the interior walls are coated. Roll it around until it stops sloshing inside. If you seem to have too much, just pour extra plaster out into the trash.

15. Leave to dry for several days. Do not store in a plastic bag. Do not attempt to remove sculpture without instructions.