I have been busy making molds and casting the bedbug model. I am trying to make it translucent since they are translucent in real life. This kind of casting comes with more complexity than when you can cast opaquely. I like to use plaster molds with clear epoxy because I can work on the mold before I cast to get it just right. In the case of the bedbug, there are sections on each of the segments that are shiny smooth. I did my best to make the clay prototype very smooth, but it always has imperfections. If I make the mold in silicone rubber, those imperfections will forever be in the cast or I’d have to grind and sand the cast. Instead, with a plaster mold, I can grind and sand the mold to get the kind of shiny smoothness I want. There may be some finish work on the cast, but less.
Just a note on the plaster molds, I use FGR plaster which was developed for inclusion of fiberglas. For the mold, I use it without fiberglas because it it a very hard plaster. Sometimes molding plaster like you get at Home Depot or Lowe’s does not work as well to give a fine, hard mold surface.
To prepare the plaster for casting, I first dry the mold completely. Then, I rub in a layer of bowling alley wax to seal it and help with the release. I buff it so all residue is removed, and then I apply a layer of vaseline. The vaseline, I have to control very carefully because I need the release, but I don’t want ridges of vaseline to be picked up in the cast-especially when I want the cast to be very smooth.
I then mix my epoxy. On the small casts like the legs, I have been using 5 minute epoxy. 5 minute epoxy will yellow over time, but in this case, that color won’t dramatically change the brownish color of the bedbug. When I get to the head louse, I will try to use a clear, non-yellowing casting material. I add a small amount of oil paint into the epoxy as I mix the 2 parts together. Not too much paint is needed to keep it translucent. I started by brushing the epoxy into the mold, putting the 2 halves of the mold together, and rotating it in my hand until it set up. I got variable results with this method, so I have started to cast each half separately and glue them together later.
I just pulled the first half of the abdomen from the mold today and it looks good. This larger cast, I did with a West System epoxy. The West System needs a different pigment than oil paint (a resin based pigment). It takes about 2 hours to set up, but I try to kick it faster by working under a heat gun (and in a fume hood with a respirator!) The epoxy cast was somewhat thin, so I backed it up with a thin layer of fiberglass. This still gives me the kind of translucency I want. I brought out the cast of the thorax and was pleased to see they fit well together.