Last time, we covered the basics of simple block-style moldmaking. While this technique is versatile and can produce very good results, it’s often not the best solution for molding complex or larger parts. The Halo Needler prop has many parts both complex and large, so we’ll need to look into other methods. But first, a little show off of the completed master sculpts all sitting pretty. Now I just need to make copies of everything!
I’m going to use the upper casing as the test mule here for showcasing a technique called “brush-on” moldmaking. The basic premise is gradually building up layers of silicone onto a part until the desired mold thickness is achieved. It’s a bit more complicated than just slathering some rubber on though, so let’s take a look at the individual steps.
First off, you need to determine if your master part will need to be molded in sections; and if so, where should the seam line be positioned. There is a significant amount of spatial organization to consider - most notably where will seam lines be the easiest to conceal and clean up later - but also things like how easily the parts will be to de-mold and how the mold will be disassembled and reassembled after use. For this upper casing, I chose to follow the lower seam line around the base of the part, then follow this hard edge line up the front. Any seam lines will be easy to sand off in these areas, and the resulting silicone mold parts will be easy to remove from the cast part. I also added a section of ¾” PVC conduit to act as a pour spout. This area will be covered up by another part after assembly, so we don’t have to worry about losing any detail here. Non-sulfur clay is used to create the parting seam, and small indentations (registration keys, as we learned last time!) are marked into the clay.