A guildmate showed me this event and I don't know the reason, what to reply to her.
She had a new chaos gem and tried to forge it somewhere. Epic Water protection, +X% to Balanced heroes, +14 whirlwind damage.
That gem (not forged yet) was allowed to be forged on any defensive item except one, Flamebound Armor (Vargulis, 2 slots, +80 res / +15 fire res / -25 water res).
Of those 2 slots, one is filled with: Rare Earth protection, -X to +Y defense, +X% to Defensive heroes.
Literally, the page doesn't allow her to forge that water protection gem there.
We excluded it could be because of Flamebound Armor negative water resistance, since the Flamebound Helm would accept it.
Is it because she tried to match Earth + Water? I thought Water+Fire and Earth+Wind wasn't allowed.
Is it because one gem has Def. hero boost, and the other gem has Balanced hero boost?
And on the future, how can we find a rule to understand when forging a couple/triplet of gems isn't allowed, BEFORE we start forging gems?
Thank you in advance for any useful reply.
(She will, of course, forge it somewhere else, but she - and then I - doesn't understand the reason)