Plaster molds are a handy tool in mass producing ceramics.
Plaster molds are used when you want to produce numerous castings of a single object when crafting ceramics. A mold, depending on the object you're trying to duplicate, can be intimidating to make on your own. Once you learn the basics of making a plaster mold, you can make your own molds in a short amount of time but it often takes a few attempts before you get the hang of it.
Instructions
1. Draw the parting line (where you'll divide the model in half) on the object you want to mold using a fine tip marker.
2. Sink the object into water based modeling clay up to the parting line and extend the clay out one inch from the widest parts of the object.
3. Smooth the clay around the object using a putty knife and let it dry to a leathery texture.
4. Apply two thin coats of shellac over the object and the clay around it.
5. Wait 20 minutes for the shellac to dry. Dust a light coating of talcum powder over the entire surface.
6. Brush a smooth coating of parting agent over the object and clay surface.
7. Nail four boards (about 8 inches by 12 inches) together to form a bottomless box. The edges of the box should not be flush so that you can separate them later.
8. Place the box on a flat surface and pack clay strips into the overlapping seams of the box to prevent the plaster from leaking out.
9. Place your object, (in the clay) flat side down, in the center of the box and mark the height of the object with a marker on the inside of one of your boards. Mark a second line about half that distance higher.
10. Mix your plaster in a bucket according to the label directions. The plaster will begin to set in about 10 to 15 minutes, so mix quickly. Wear a dust mask to avoid inhaling plaster dust.
11. Pour the plaster into the box, filling up to the second mark you made. Leave it to harden for at least 30 minutes.
12. Knock the boards apart with a hammer. Turn the plaster mold over to lift the clay from the model object and plaster.
13. Clean off the shellac from the plaster half of your mold using alcohol.
14. Repeat steps 2 to 6 but flip the object over this time so the opposite side is face up in the clay.
15. Repeat steps 7 to 13 to cast the other half of the mold.
16. Remove the model object from the plaster. Clean away plaster particles and any shellac using alcohol.
17.Carve small round depressions (keys) into the upper surface of each mold using the rounded end of a spatula. The depressions should mirror each other when the molds are placed together.
18. Carve the pour hole (carved opening in mold to pour ceramic or porcelain into), which can be in one or both halves of the mold, using a round file.
19. Bevel the outer edges of the mold and the edges of the parting lines using a rough round file to prevent chipping.
20. Allow the mold halves to dry for 4 to 5 days before using.
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