Resources:

• Douglass and Sturgess (888) ART-STUF
  D&S carries a wide range of prop building materials. At a minimum, you need RTV Silicon to make the molds, universal mold release and two-part odorless urethane resin. Other recommended items include Ultracal 30 for making mother molds, both wax- and water-based clay, naptha solvent to clean the parts after they've been cast, and various bronzing powders.
• Silpak, Inc. (909) 595-6191
  Another good source for silicone rubber and urethane resin casting materials.
• The Prop Builder's Molding and Casting Handbook, Thurston James
  The sequel to James's The Theater Props Handbook, this is the second book in the author's crafts trilogy. Properties master of the UCLA theater department, James provides concise, step-by-step instructions on molding and casting procedures using some 30 different materials from papier mache to the new rubber materials. Some 450 illustrations enhance the text.
• Davis Dental Supply Co. (818) 983-0030
  Dental acrylic comes in a fine white powder that dissolves when a monomer liquid is applied. It dries into a very hard, translucent plastic that is extremely tough and durable. A bit pricey but great for reinforcing hidden seams for added strength.

Specialized Tools:

• Electronic Scale
  Useful for weighing correct amounts of resin. You'll want a scale that's accurate to the nearest gram. If you mix smaller amounts then a scale that's accurate to a tenth of a gram is better but also more expensive. As a general rule the more accurate the scale the less total weight it can measure.
• Vacuum Pump and Chamber
  Used for degassing the silicon rubber. Vacuum pumps are rated in terms of draw (how hard a vacuum it can pull, expressed in inches of mercury) and CFM (how quickly it can pull a vacuum). The pump doesn't have to pull quickly but it does need to pull at least 27" in order to degass the rubber. After the rubber and catalyst is mixed, the rubber is placed in a vacuum chamber for degassing. During this process the rubber will expand to twice its original volume so make sure it's in a large enough container. The rubber will expand and look like it's boiling. After the "boiling" ends the rubber is sufficiently degassed and can be poured over your part. If the part is not hollow, you can degass the rubber a second time after pouring it over the part. This helps eliminate any air bubbles trapped next to the part when pouring the rubber.
• Air Compressor and Pressure Pot
  Used to minimize air bubbles in cast parts. You can only do this if you've degassed the rubber mold. After pouring resin into the mold, place it into a pressure pot and pressurize to 50-60 psi until the resin hardens. You can use a spray gun paint pot for small molds.

Urethane resin has been a godsend to prop builders everywhere. Poured into silicon rubber molds, its low initial viscocity enables it to reproduce details smaller than 0.001" wide. Pictured here are two urethane mausers--one right after it was pulled from the mold and the other after it's been painted and transformed into a Star Wars blaster.