Making the Mold

  1. Design the model.  You can use a found object or design a prototype from clay or plaster.    
  2. Prepare the mold.  

Determine how the model will be cast and the number of parts for the mold.

Use cottle boards to create a retaining wall for the plaster.  

“Size” the mold with several layers of mold soap.  

Fill all seams with clay to prevent seepage 

  1. Calculate the amount of plaster needed.  

First, find the volume of the model and the volume of the mold.  

Then subtract the volume of the model from the volume of the mold.  

Convert that number from cubic inches to number of quarts needed by dividing by 80.  Cu. in. ÷ 80 = number of quarts of water.  

Use the chart on the back to find the amount of plaster.    

  1. Add the plaster to the water

Use room temperature water and sift the plaster into the water. 

DO NOT MIX YET  Allow the plaster to soak into the water for 5 minutes.

Mix for 2 to 3 minutes, with a drill or by hand.  

Tap the bucket to get all the bubbles to rise to the surface, scoop them off or spray with alcohol.      

  1. The plaster is ready to pour when you drag your finger across the surface and a faint trail is left behind.  
  1. Pour plaster slowly.  Try not to splash.  Do not pour the plaster directly on the mold because it can cause an indent on a clay model.  
  2. Tap the table to get all the bubbles to rise to the surface.
  3. Allow the mold to sit for at least an hour before removing the cottle boards. 
  4. Clean up the mold.

Use a surform and sandpaper to soften edges.  

Use vinegar to remove mold soap.    

  1. Wait until the mold is dry before casting.  Do not apply heat to the mold.  This can cause the mold to become soft and crumble.     

References:

  • Arbuckle, Linda, http://lindaarbuckle.com/handouts/plaster.pdf
  • Frith, Donald, Mold Making for Ceramics. Iola, WA: Krause Publications, 1985.
  • Gringhuis, Karen, and Val Cushing. Cushing's Handbook: A Compilation of Papers Concerning Glazes, Glaze Calculation & Formulation, Clay Bodies, Raw Materials with Clay Body, Slip and Glaze Formulas, Firing, Pottery Making Tips and Other Useful Information. Alfred, N.Y: The author, 1994. 
  • Laguna Clay, How to Make and adjust casting slip.  http://www.lagunaclay.com/support/art-of-slipmaking.php
  • Martin, Andrew, and Andrew Martin. The Essential Guide to Mold Making & Slip Casting. New York: Lark Books, 2006. 
  • Skee, Stanley, and Charles Chaney. Plaster Mold and Model Making. New York: Van Nostrand Reinhold, 1973. 
  • Wardell, Sasha. Slipcasting. Ceramics handbook. London: A. & C. Black, 2007.