How to Make a Mold for Cast Metal

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Molds are helpful when casting duplicate metal pieces. They greatly reduce the amount of work required to cast metal and are ideal for creating numerous identical sculptures, figurines and pieces of jewelry. The process of making a mold can be difficult and time consuming. However, the mold will prove invaluable to the duplication process later on.

Things You'll Need

  • Clay
  • Pallet board
  • Model to be duplicated
  • Clay working tools
  • Small funnel
  • Plastic-coated electrical wire
  • Foam board
  • Hot glue gun
  • Plastic wrap
  • Measuring cup
  • Release agent
  • Mold making rubber
  • Roll the clay on the pallet board thickly enough to press half of your sculpture, or other model, into.

  • Press the sculpture halfway into the clay, so that half of the model is pressed within the clay and the other half is sticking up out of the clay. A mold for the other half of the model will be constructed later.

  • Use clay working tools to level off the clay around the model, and press it in to fit the model's contours.

  • Press a funnel-shaped object into the clay to preserve a funnel or opening in the mold. The funnel should lead directly to the model, as this is how the metal will be poured into the mold. Also press plastic-coated electrical wire into the clay to preserve air channels leading to narrow or high points of the model, so that metal will be able to flow to those places within the mold and not be blocked by air pockets.

  • Cut the clay away in straight lines approximately ¾-inch from the model. Make sure you cut directly against the top of the funnel, as it must be on the edge of the mold so you can pour the metal.

  • Construct a foam board wall around the remaining clay that is ½-inch higher than the highest point of your model. Press clay into any gaps between the wall and the clay you have already prepared. Hot glue the bottom of the wall to the pallet board.

  • Place a piece of plastic wrap over the top of the model, and pour water on top of the plastic wrap with a measuring cup. Note how much water it takes to fill the space to the top of the foam board, as this will let you know how much rubber to mix.

  • Remove the water and plastic wrap from the model, and coat the model and the clay with a release agent. This will keep the rubber from sticking to the model or the clay.

  • Mix and pour the rubber onto the model to prepare the first half of your mold, filling it to the top of the foam board.

  • Allow the rubber to cure by allowing it to sit undisturbed for approximately 24 hours.

  • Remove the foam board wall, the funnel, the wires and the clay from the rubber to reveal the first half your mold.

  • Repeat the above steps to create the second half of your mold, using the opposite side of your model.

    As an alternate method, at the end of Step 10 turn the first half of the mold over and remove every bit of clay. With funnel and wires in place and walls reassembled, apply a release agent to the surface of the rubber of the first half of the mold (and to the surface of the model), and pour the rubber for the second half of your mold onto the first, which would insure a better fit for the two halves of the mold.

Tips & Warnings

  • Purchase a release agent and mold-making rubber at hardware stores or online.
  • Pour the rubber into the molds slowly and let it slowly rise to prevent air bubbles from getting trapped in the rubber and deforming your cast piece.

References

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