I took the sculpted red gemstone for Shalamayne's hilt and created a silicon mold so I can cast gems in translucent red resin. I used Tap Plastic's RTV silicon, it was much more viscous than I expected, next time I'll need to use more rigid mixing containers.
I built the mold using the top of a drink cup and the lid of an old container. I used hotglue to seal the cup to the lid, then a dab of hot glue to secure the gem in nearly in the center.
For my first attempt at a mold I think it turned out pretty well. There was a little leakage around the edge of the gem, so the very bottom edge of the gem will be uneven, but that part will be hidden when the gem is incorporated into the sword.