Second Blacksmith research

[Touchpad Warrior]

Is the 1k crowns a one time thing, meaning you pay that and unlock the second research forever or do I have to pay it eveytime I want another research to be made at the same time?

 

[Touchpad Warrior]

And by blacksmith I mean Armory

 

[aquawind]

Pay once and have the 2nd upgrade slot unlocked permanently.