The rock shard you imbued should be powerful enough to break the runic magic binding my brothers.
Take it with you and find the runed giants walking north along the Eastwind Shore. Unleash the power stored in the stone and observe the results.
If it works, the runed giants should return to their senses and stop obeying the iron dwarves. If the stone fails to work, the giants may attack in a weakened state. But, what choice do we have? If we do not try, they will remain enslaved without hope.
So it's an uncertain thing? I wish it was not a matter of chance, but at least we're on the right path. Without your help, this wouldn't have ever been possible. Should you learn any more about the machinations of the iron dwarves and their plans toward the children of stone, seek us out and we will hear you, <name>.