Did Gandalf make a mistake at Isengard ?

[Inziladun]

Originally Posted by Formendacil

Although the basic point here that Inziladun and {b]Ibrin[/b] are making is to the effect that the palantír did not play a deliberative role in Gandalf's actions, I think it's incorrect to say that he did not know a palantír was in Saruman's possession.

The Orthanc-stone, after all, had always been at Isengard. Unlike the stones of Arnor, it was never moved due to enemy advances, and unlike Osgiliath and Minas Ithil, Orthanc was never taken by an enemy army--though, if my memory serves (and it IS hazy), the garrison did become strongly Dunlendish at some point, and resist Rohirric influence.

If Gandalf was so certain of Saruman possessing the Stone, why would that not have been his first assumption of the manner in which Saruman and Sauron communicated?

There was some link between Isengard and Mordor, which I have not yet fathomed. How they exchanged news I am not sure; but they did so.

TT The Palantír

Surely, if Gandalf had been fully aware of the Orthanc-stone, it would not have taken Pippin's experience on Dol Baren for him to recognize what the Stone was.
Unlike Saruman, Gandalf's mind did not have a special affinity for artifacts of power, and I can see how the palantíri would have eluded his attention. It certainly appears to me that the event on Dol Baren took him completely by surprise.