Track molding and casting
This post shows the tank track mold making and casting processes. I got this right through a bit of trial and error…
In the first image, you can see the primed & varnished tank tracks covered in a thinned silicone caulk mixture. I use about a 30:70 mixture of lighter fluid mixed with Type I silicone caulk. I apply this in a thin-ish layer, just so it brushes over details easily.
(This is the reason for first priming the master model, then applying varnish: the primer seals the piece, so that the varnish has a sealed surface to smooth over. Without the varnish, the silicone grabs onto the rough surface of the primed master; without the primer, the varnish sinks into the surface and again the silicone grabs onto the rough surface of the master - you end up with your master embedded in very hard to remove silicone)
After the thinned silicone has dried (about an hour or so), I apply a thicker layer of silicone, which I prepare by dunking silicone caulk into a container filled with water and some dishwashing liquid. I massage the silicone in the water for about 2 minutes, trying to expose all of the silicone to the water (the soap is just there to make sure the silicone doesn't stick to my hands). I then take the silicone and apply it on top of the dried silicone, so that the mold will have some volume. You can see this in the second image.
This can be left to dry, preferably overnight, before making the first cast. I do this in a Hirst-arts-fashion, by pouring some casting plaster into the mold, scraping the excess off, and then letting it dry for a bit. You can see this in the 3rd image. The plaster I use is called Skullduggery Perfect Cast, but you can probably use any kind of plaster or dental stone for it.
The 4th and 5th images shows the results of the cast: perfect little tank tracks. They are not super strong, but I will be gluing them onto the surface I made in the tread hulls, so it all turns out pretty good.