Casting

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.

Pouring plaster over the clay prototype to make the mold. Note, the bottom half of the mold is already done.

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.

Finished mold

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.

Epoxy cast (colored intrinsically with oil paint) of the bedbug foreleg

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.

Cast of the thorax and abdomen

Thorax and abdomen together

 

Advertisements
This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s