This thread is devoted to techniques for making rubber molds and casting duplicates in resin. I have used this technique for many projects and find that it is ideal for situations where you want either multiple copies of any object or you want a more durable item than that which was created originally. The final resin product is relatively strong (if large enough) and is completely weather proof.
Rubber molds can be of two varieties. The first is a simple 1-part mold where one face receives the molded form and the other side is flat. The second type is a 2-part mold where the mold is made up of 2 halves and the resin is poured through a hole and the resulting item has molded surfaces on all sides. The example that I will use (because it is one where I photographed the process) is the Casey Jr. rolling stock.
Casey Jr. Rolling Stock
The rolling stock of the Casey Jr. Circus Train at Disneyland (not as seen in Dumbo) has highly sculpted relief on the sides. I decided to form the sculptures out of Sculpey polymer clay and then cast the sides in resin with a 1-part rubber mold. First, I drew plans that were sized to allow the new cars to ride on Hartland short flat cars. I then printed out the drawing of the sides of the cars and glued them onto an acrylic backing that could be placed in the oven. The clay was applied to the drawing using photographs as a guide. Another Burnslander, Rob Fendler, used this same approach and achieved some remarkable results. Hat's off to you Rob. My sculptures were not nearly as clean, but I did what I could.
The Sculpey was then baked and the hardened clay was then sanded to try and smooth out rough spots. These pieces were then glued to a car side and the side was placed in a foam core box which was easily made with hot melt glue. The car side is now ready to have a mold made of it. The rubber is a 2-part silicone which was purchased online at micromark.com. The item and the mold box are first “painted” with a clear mold release agent. The rubber is them mixed in a one-to-one ratio and poured slowly (to avoid air bubbles) into the box. Be sure that the box is sitting on a level surface.
Once the rubber has cured, about 4 hours, I usually tear the sides of the mold box off so that I can delicately remove the mold from the original. Experience will teach you how certain sculpted forms can produce a rubber mold. If you have thin little crevices in your original, the rubber will usually tear once it gets too thin in the crevice. This can lead to unevenness in portions of the work which may or may not be desirable.
Now that you have a mold, all you do is mix up some 2-part resin and pour it in! The resin comes in 2 speeds. The quick setting 300 series is great if you want to knock out lots of simple pieces in 1-part molds. The slower setting 600 series is more appropriate if you have to slowly pour the mixture into a small hole in a 2-part mold as the quick setting variety will start to thicken before it gets into the mold.
Add some brass rods, sheet acrylic, tiny wood tunings and paint and you've got Casey Jr.!
If anyone is interested, I can discuss 2-part molds, but I think I’ve gone on long enough here.