Experiment 24: Gallium & Coins

A while ago, I carved a template pirate booty coin from some thin plywood using my woodcarving knife.  Recently, I got gallium metal (wahoo!), so I decided to make a mold for the wooden template.  I used plaster of paris and just poured it over the coin in a cardboard tube.  After it had dried, I pried the wood coin out.  It broke the mold a bit, so I had to do surgery with epoxy and superglue.  Then, I melted the gallium in a double-boiler setup over my hotplate.  I have found that the gallium tends to get a layer of slag on top if it is submerged in water.  The gallium cast very easily when molten and stayed molten... and stayed... and stayed.  Turns out, gallium has a (very strong) tendency to supercool, which means that the liquid will cool to below its melting point of 85°F and still be liquid.  This property can be great, but it is very annoying if your gallium coin never freezes.  To remedy the problem, I added a crystal of solid gallium.  This seed crystal jumpstarted the freezing process and in a reasonable amount of time, the gallium froze.  When tried to remove it from the clutches (notice foreshadowing) of the mold, the mold flatly refused to let go.  In the end, the mold broke completely and the gallium pirate booty coin turned out great!  I am very pleased with how the design turned out.  Sadly, the coin met its end in a hot car on a sunny summer day (it was "experimentation"), but I plan to resurrect the pirate booty coins by making a new mold and being more careful.