Right now, the melting crucible has three tiers:
2000K
2500K
4000K

For my pack, I would ideally like these to be at 1300 (bronze age), 1750 (iron age) and 4000 (steel age)

You think we could get a config option for those cutoffs?

I'll make a PR for this myself, I just need to look into how to dynamically show the correct number in the tooltip.