After hours progressing through Industial Revolution (IR), I hit a wall starting at Mk3 level items because electrum is required. IR provides no way to alloy the needed electrum, though I believe the IR Solid Infuser can be used to do it in other mod packs. There is no IR recipe for electrum in REI. The only recipe to alloy electrum in this whole mod pack is using Modern Industrialization (MI) mixers, so you have to start that mod just to continue with IR. I can’t believe this was intentional?

TR also runs into an issue with needing MI. MI is the central tech mod of the pack

You can use Create heated mixing, or the TR machine to get electrum though. click the > icon at the top of the tabs in REI when looking at ingot recipes