The top shell of Tracer’s pistol is my favorite element of her gun. i don’t know what it is about it, but it’s the piece that puzzled me the most leading up to this project, and I’ve run through the process of building it over and over in my head. 3D printing made constructing the for much easier, but there’s still the issue of casting it in resin. I originally thought I could use the same two-part mold approach I’ve been using for many of the components, so I gave that a shot.

I tried dividing the mold down the middle. The advantage here would be that any seam line would be hidden under the pieces that make up the sight on the top of the gun. In the photo above you can see that the through-holes are taped off with clear packing tape so the part didn’t get trapped inside the silicone. Unfortunately, after pouting both halves I went to rescue the part and found that the complex geometry of the shape made it impossible to extract without destroying the mold. So I did some research learned about the squish mold approach.

The car body in the example above has a lot of similarities to the geometry of the top shell component of Tracer’s gun. It’s symmetrical down the middle, but there are various compound curves, through-holes, and overall has a “shell” like quality. Creating a squish mold would allow me to isolate complexities like the ventilation holes to the top half, while isolating the complex geometry to the bottom half.

The first step was to create a base that isolated the top and bottom elements. I did this with clay but forgot to take a picture of it, but here’s the equivalent shape in silicone:





Again, clear tape acts as a thin barrier behind the through-holes to keep them isolated to the top half of the mold. This was the hard part, and took some careful planning and some imagination as I pictured how the silicone would be poured over the part while allowing the cast piece to be safely removed. Here you can see the resulting two halves of the mold:

The setup for this was more time consuming than a one-part mold, but this method has its benefits. For one, since you’re squeezing out excess resin through the bottom, there aren’t seam lines in the traditional sense. Also there’s no need for a pouring spout because you pour resin in before putting the two halves together. The process is a little messy:

Somehow, it worked on the first try. I’m so thrilled with the result. It feels incredibly satisfying to hold this complex form in my hands in the final material (and close to the final color!).