I did try to do molds myself some time ago in school and could never really get a nice working one. I think it's an art to cut rubber molds correctly. This one is actually a pretty simple ring shape and not that hard to cut. In comparison some molds I got for my Mermaid rings are awesome with all those undercuts and multi-part pieces. Nowadays I send my masters out to get a professional cut mold. Those work so much better when I do the wax injection. It also saves me from all those bloody cuts in my fingers from the cutting scalpel. If any one cares and want to try it out on their own, here is a pretty good description on how to make molds.
Here the master model and some wax copies from the mold with the injection and casting sprues on them. The master has to be larger than the final intended ring and setting to allow for shrinkage. This pink rubber has less shrinkage that normal rubber (about 2% vs. 8%) but also during the casting there is shrinkage from the wax to the final cast metal.
This mold will help me to speed up the Tetra ring making for the 10 mm stones. I still have to adjust the settings slightly for some of the stones. There are always slight differences in the trillion shaped stones I got. Some stones have a bit rounder sides or rounded or pointy tips or even deeper or shallower cuts. But adjusting the setting is so much faster after having the main shape already there. Then all else I do is sizing the band in wax correctly and send it out to the caster. I try to avoid sizing and soldering in metal and usually cast every ring to the intended ring size.
Here are a few new Amethyst colors I recently got in darker shades. For the smaller stones and fancy cuts I will still have to hand carve each ring separately and cant use the wax models from the mold.