How do you unlock the ability to upgrade weapon gems?
I've seen the ability to merge together older gems into upgraded ones in several reviews but haven't unlocked this in the game yet. I'm sure I'll find it soon enough, but if it's hidden in some semi-obscure side quest it would be nice to know so I can unlock it earlier rather than later.
Solution 1:
It happens automatically after you get to a certain point in the story. Just a little past 40% completion when doing all the side missions. (trying to avoid spoilers)