It might be beyond your coding ability to implement, but can you re-use/add modified gem tumbler code to this mod so that the player can use lathes to cut gems (since that's sort of how it's done in real life)? That is only a 1 to 1 exchange, so it shouldn't have as many issues as trying to convert nuggets into ingots (although the wire extruder code in beta could probably also be adapted to accomplish the same thing converting multiple nuggets into a single ingot; however, it's still in beta, so not worth it anyways until beta transitions to vanilla).