I recently made some props for a local theatre group that was producing a musical version of "The Legend of Zelda: The Ocarina of Time." One of the key props from all the Zelda series are the "rupees", a gemstone used primarily to purchase items within the game. The theatre group wanted a red, green and blue one for their performance. I needed to come up with a way to make them cheaply and precisely, because the group wanted their props to be as accurate to the game as possible.
I thought about casting them, but casting translucent items is costly, messy, difficult and hazardous. I thought about cutting out individual pieces of plastic and gluing them together, but that would be time-consuming and would be difficult to make the seams look good.
I had a flash of inspiration when I thought about vacuum forming. I could easily cut a piece of wood to look like half of the gem, vacuum form two halves, then glue them together. This would also make it dead simple to repeat for all three rupees, making each of them match.
Step 1: Making the Form
In vacuum forming, you heat a sheet of plastic until it is completely flexible, then stretch it over some kind of form, and vacuum all the air out so the plastic sucks in tight against that form. When the plastic cools, it retains the shape of the form. I wrote an Instructable about the homemade vacuum former
I was using.
To make the rupee form, I used a piece of oak I had in stock. I wanted something hard that I could get clean lines on. I cut the shape out using my table saw, then set the blade at an angle to cut the bevels into the edges. It only required very minor sanding to clean it up.
Step 2: Vacuum Forming the Halves
I bought some fairly thin acrylic (Plexiglas) at Hobby Lobby. After vacuum forming it over the wooden form, I carefully cut it out with my Olfa knife, leaving the piece you see below.
Because I was making three rupees, I needed six of these pieces.
Step 3: Painting
Before gluing the halves together, I painted the insides. Painting the insides made it impossible for the paint to wear away while being handled by the actors. It also allowed the outside to remain smooth.
For the green one below, I tried watering down acrylic paint and applying it to the inside. It worked, but it was difficult to spread it evenly and it kept wanting to bead up. For the blue and red rupees, I switched to spray paint and just lightly dusted the insides to give them the right color while retaining their translucency.
Step 4: Gluing
To glue them together, I used a solvent-based clear adhesive that works on plastic. The particular brand was "Amazing Goop", which has a bit of thickness and body to it; this was helpful because the edges didn't match up completely, so there were some intermittent gaps around the circumference. Acrylic can also be glued with model airplane glue and super glue.