Molding Material

• One of the best materials for making molds to cast replicas of sculptures, toys, natural materials, mechanical parts or any items for reproduction is a latex rubber compound. A rubber mold allows for the capturing of fine detail, and the flexibility of the mold allows for release of undercut areas and forms in-the-round. There are many commercial molding products available, but in the author's experience, some of the best results are achieved using Rub-R-Mold flexible molding compound.
  
  

Settiing up Container for Mold

• Sculpture to be molded
  
  Place the item you wish to create a mold from on a smooth, clean, non-absorbent surface such as glass, ceramic or plastic. In the example pictured here, a small sculpture with a flat base is used. Add an extra layer of clay underneath the item as a spacer to allow for extra room in the mold, to ensure that the mold will be completely filled, allowing for shrinkage.
  
  

The Container Wall

• Mold-container wall
  
  Create a container around the item using oil-base or polymer clay. Form a long, flat strip of clay of sufficient height to rise at least one-quarter inch above the highest part of the item. Place the clay strip around the item in an elliptical shape and join and seal the ends. Allow at least one-quarter inch of space between the container wall and the item's surface. Ensure that the bottom edge of the container is adhered to the glass or plastic base, firmly sealed to prevent any leakage of the molding compound from the container.
  
  

Mixing Components

• Molding compound
  
  Mix the two components of the Rub-R-Mold. Use the chart supplied with the instructions to calculate the relative quantities to mix together for the volume you will need to fill the clay container and cover the item you are using to create the mold.
  
  

Pouring the Mold Mixture

• Pour the mixed compound in a smooth, narrow and steady stream from one end or side of the mold. Fill the mold slowly and and allow the mixture to flow around the item, filling in crevices and details without creating bubbles on the surface. Vibrate the container by tapping periodically on the glass, ceramic or plastic base to help dislodge any bubbles on the surface of the item or in the mixture. When the item is completely covered, allow the compound to congeal according to the manufacturer's timescale, which varies by the volume of the mixture.
  
  

• Remove the clay container walls and carefully lift up the mold. Check that the mixture has fully cured to a firm but flexible consistency. Gently remove the item by flexing and stretching the mold. In cases where there is a deep undercut or partially surrounded projection of the item, it is sometimes necessary to make a small incision in the wall of the mold to free that part of the item. However, care should be taken not to pierce all the way through the mold wall when making the small incisions.
  
  

• Wash the mold with warm, soapy water inside and out to remove any film or residue. Rinse thoroughly and allow the mold to air-dry. Inspect the mold carefully. If it is free of any residue, and completely dry, the mold will be ready for pouring castings. Wax, plaster of paris, cement and casting resins are common materials used in casting. Follow the manufacturer's recommendations for materials that are compatible with the molding compound. Refer to the links in the resource section below for an online supplier of molding materials.