I can't believe I didn't think of this before

[BigJMoney]

If you wanted to have an ability that affected the conversion of gems to gems, I think that it could be done like this: "Fire Alchemy" or "Nature Alchemy", etc. Basically, it would mean when converting to or from the specific type of gem and astral pearls, you get a 1:1 ratio. Not all gem types in the game would necessarily need an alchemy ability, either, if it doesn't seem thematic. Using Dominions II as a water mark, I don't know what nations could use an ability like this, though. You'd think Ulm could use it, but it doesn't seem thematic. Not unless you gave the Master Alchemist Fire Alchemy and Earth Alchemy.

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