We know that Gandalf was given Narya, the Ring of Fire (one of the Elven three) by Cirdan the shipwright. When Saruman imprisoned Gandalf, why did he not attempt to take the ring from him? It would seem logical because Saruman was hungry for power. Or did he not know that Gandalf possessed such a powerful ring?
We learn about Saruman's knowledge of Gandalf's possession of the ring in Unfinished Tales:
And the Grey Messenger [Gandalf] took the Ring, and kept it ever secret; yet the White Messenger [Saruman] (who was skilled to uncover all secrets) after a time became aware of this gift, and begrudged it, and it was the beginning of the hidden ill-will that he bore to the Grey, which afterwards became manifest.
We aren't told exactly how Gandalf conceals the ring, or when Saruman became aware of the gift.
It is possible that Saruman became aware of it after Gandalf escaped from his imprisonment, perhaps even after the Valar sent him back after fighting the Balrog, and so learnt of it too late to attempt to take it. However, that doesn't seem likely, since the knowledge was the "beginning of the hidden ill-will", and that presumably existed prior to the imprisonment (otherwise the beginning would have been the refusal to reveal the location of the One Ring).
So it seems fairly likely that he did have prior knowledge. The two most likely explanations for not taking it (or attempting to) are:
- Saruman was unable to take the ring, either because it was concealed somewhere other than on Gandalf's person (it is magic, and he is a wizard), or because Gandalf would have been able to prevent this. Although the (Jackson) movie shows a great magical battle between Saruman and Gandalf, this doesn't appear in the book - he is imprisoned in a much more mundane way, and doesn't resist (presumably because it would have been futile).
- Saruman was at this point fixated on the One Ring, and certain that Gandalf would eventually concede defeat (he believed there was no escape) and reveal its location. His fixation on the One, and confidence that he would soon possess it, blinded him to thoughts of Narya.
Probably because Saruman considered Gandalf's Ring useless to him. Elrond says of the Three Rings generally,
[T]hey were not made as weapons of war or conquest: that is not their power. Those who made them did not desire strength or domination ... but understanding, making, and healing, to preserve all things unstained.
from "The Council of Elrond" in "The Fellowship of the Ring"
At the time he gave it to him, Cirdan the Shipwright tells Gandalf about Narya specifically,
For this is the Ring of Fire, and with it you may rekindle hearts in a world that grows chill.
from "The Tale of the Years", Appendix B to "The Return of the King"
Cirdan's words suggest that Narya's most important power (or at least its power that would be most important to Gandalf) is an ability to awaken hope and the will to survive in the hopeless. No doubt its power was at work when Gandalf and the knights of Dol Amroth rallied the spirits of despairing Gondorians during the siege of Minas Tirith.
Saruman, as Middle-Earth's second greatest authority on the Rings of Power, would have known all this; and known, too, that the Three Rings of the Elves "endure no evil", as Gandalf says to Frodo. Perhaps this last consideration carried weight with him. His words to Gandalf
We can bide our time, ... deploring maybe evils done by the way, but approving the high and ultimate purpose: Knowledge, Rule, Order
from "The Council of Elrond" show that he is aware that he is doing evil, whether or not he still deceives himself that good is his ultimate aim.
Treebeard characterizes Saruman thus:
He is plotting to become a Power. He has a mind of metal and wheels; and he does not care for growing things, except as far as they serve him for the moment.
from "Treebeard" in "The Two Towers"
Saruman's attempt to desolate The Shire seems to bear out Treebeard's description. Making, healing, and understanding are not high on his priority list.
In any case, at the time Saruman captured Gandalf he hoped for either of 2 outcomes: if Sauron triumphed, to use the power of his Voice to become the power behind Sauron's throne; or to use the One Ring to crush Sauron and become ruler of Middle Earth in his own right. Saruman knows that even with the Ring of Fire, Gandalf is no match for Sauron; he probably won't be either, so it can't help him defeat Sauron. Nor was it likely to help him manipulate Sauron; and in the event of Saruman becoming Sauron's servant, there would be a very real danger of Sauron discovering that his new adviser possessed one of the Three Rings -- with probable bad consequences for Saruman and his plans.
This is an old thread but I wanted put one more possibility out there that doesn't seem to have been considered.
Saruman didn't take the ring from Gandalf because he couldn't. In my mind it was always apparent that the trapping of Gandalf was a stalemate.
Saruman shows his hand here. He reveals his plans to Gandalf in the hopes of persuading Gandalf to his side. Why waste your energy on a nobody? Gandalf is a major player in the moving of the world. While Saruman may belittle or mock his efforts Saruman in no way under estimates Gandalf's influence. If Saruman could not persuade he certainly would have tried to destroy.
Saruman did not have power enough to destroy Gandalf. Indeed, Gandalf likely could have retreated, were not for Orthanc itself which allowed Saruman to trap and hold Gandalf. This was not defeat. Though more powerful, Saruman did not have sufficient means to put an end to the threat that Gandalf represented to all his plans.
Gandalf had sufficient power to protect himself and his possessions as alluded to in other answers concerning his staff.
Perhaps Gandalf had the foresight to leave his ring in Rivendell before visiting Saruman. He often acted on such insight without fully understanding why he was doing so at the time. For example, while he was still confiding in Saruman about many things, he instinctively avoided telling Saruman anything about his own dealings with the Rings of Power. (Even though he knew of Saruman's obsession).
Though the idea of Gandalf stashing Narya is probably logistically very difficult to reconcile.
Another possibility is that Gandalf was imprisoned with Narya, and Saruman had every intention of taking it from him, but was waiting for the right moment to do so. He knew Gandalf had the ability to deliver a much bigger prize, The One Ring, and was still hoping that he could bring Gandalf around to his side. Stripping Narya from Gandalf was less pressing, and could decrease the chances of gaining his cooperation.
I assumed only ring-bearers could see the rings of power, bar The One Ring which obviously could be seen by everyone (unless of course that's only because it wants to be seen), as displayed by Sam being unable to view Galadriel's Ring seeing only a star between her fingers whereas Frodo could. Whether Saruman being a wizard or because he had forged his own ring makes any difference I'm not too sure.
Narya would give Saruman no power that he would find useful. It's virtue is that of assisting others with strength of mind and courage and fortitude. Saruman's goals are the opposite. He doesn't injure only to realize his goal of mastery, but also for the sake of injury itself as he says openly and plainly when Gandalf and company meet him on the road after Treebeard releases him from Orthanc. With such goals, Narya would be useless, or perhaps even counterproductive.
The One Ring was created with the intent to control everyone bearing a ring of power. (That might not be its only power, but it's a goal.) At least that's how I interpret the inscription:
One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them
As Saruman's plan was clearly getting the One Ring, this made having any other ring of power almost useless to him. If Saruman got the One Ring, he could hope to use it to break Gandalf's will if and make him his slave if he still has the ring, or use someone else if Gandalf will have since given the ring to someone else.
Just to elaborate on @DaveGorman as I coincidently found some information in the LotR wiki - Saruman could not have seen Narya because he was not in possession of the One Ring (emphasis mine):
These rings are invisible instead of making the wearer invisible. Galadriel revealed her possession of one of the rings to Frodo while he was in Lothlórien after he saw her ring. This is because of his possession of the One Ring. Later, while traveling down the River Anduin, Frodo spoke of it to Aragorn, who admonished him not to speak of it outside of Lórien.
As @TonyMeyer already pointed out, Saruman was aware of Gandalf's possession of Narya but it was possible he wouldn't have been able to view it.
The Three Rings seemed to have been crafted to help counteract the effects of the curse pronounced by Mandos during the Flight of the Noldor from Valinor. After all, the wearers of the Three had elected to stay in Middle Earth after the War of Wrath. As noted above, Saruman had no use for the powers of Narya.
It is likely that Saruman still had hopes of converting Gandalf to his side as stated by someone in previous post. Taking the ring by force could well have been counterproductive to in this, and besides, having Gandalf as his prisoner was paramount to having the ring anyway. He could afford to bide his time even if the ring could have added to his power in someway. Also, as someone has all ready stated, it might not be that easy to take by force. Given all that and the nature of the rings power, Gandalf as an ally would probably have been a much greater asset than just the ring itself, so it is unlikely he would just give up without putting a lot more effort into that. The ring would always be there should he fail.