I've just discovered the thing, you can make any incarnate into any element, without even needing for surface. You need 1 point into certain spell school and a book for it i.e. any of conjurer and geo skill would result into poison infusion. 1AP cost, changing incarnate into posion with poison dart. I dont know how does it affect cooldowns as of yet but thats something.
Then if you want like acid incarnate you need Acid infusion book, made of Corrosive Spray and Summon Incarnate (not sure if it has to be summon but i have tested it with it).
E/ tested, works with any conjurer and probably any tier 2 book of the element. Created blessed ice infusion off Steam lance just now.
That is really cool. Great find. I was able to combine a Summon Incarnate with a lvl 1 Poison Dart book for a Poison Infusion Skillbook. It's 1 Memory and 1 AP to change the Incarnate's element to Poison. I'd wager this works with most elemental skillbooks.
This could be useful as changing the element grants another ability that is off-cooldown, and could also be used to change the damage type when swapping to a new enemy. I'd hate to have to allocate a point of memory towards every infusion element though.