Can I ask questions on this SE regarding things such as gem tumbling, cabbing, and faceting here along with concepts such as gem "fire"? I'm guessing not, at least to the first, because that's more of an artistic concept rather than a science based concept. But other people's thoughts would be appreciated.
I think questions on rock cutting and gem cutting for artistic or industrial purposes is off topic for Earth Science stack exchange. Some aspects may be on-topic, such as scientific aspects of rock formation and how this affects hardness and other properties relevant for artists. But there is currently no Stack Exchange site where the artistic or industrial aspects are on-topic.
Potentially, you could propose to broaden the scope of the proposed Metal working site to include working on rocks and gems. Unfortunately, that proposal appears to move rather slowly so it doesn't appear too likely it's going ahead (with or without broadened scope).