[Lalwendë]

The Osanwe-kenta should illuminate a lot about this question. It has a long note about the wself-arraying of the Ainur, and the main point is that the longer one of them takes on a hroa, the more of a 'habit' this becomes:

if a "spirit" (that is, not one of those embodied by creation) uses a hroa for the furtherance of its own personal purposes, or (still more) for the enjoyment of bodily faculties, it finds itself increasingly difficult to operate without the hroa.

It also specifically mentions Melkor and his quest:

to become Lord of the Incarnate, and of the great evils that he did in the visible body. Also he had disspiated his native powers in the control of his agents and servants, so that he became in the end, in himself and without their support, a weakened thing, consumed by hate and unable to restore himself from the state into which he had fallen.....So it was also with even some of his greatest servants, as in these later days we see:they became wedded to the forms of their evild deeds, and if these bodies wree taken from them or destroyed, they were nullified, until they had rebuilt a semblance of their former habitations, with which they could continue the evil courses in which they had become fixed. (Pengolodh here evidently refers to Sauron in particular...)

And this also applies to Sauron. We know that Sauron created the Ring when he was still 'hale' in his hroa, even beautiful in the form of Annatar; it was much later that his bodily form was harmed and he had to lie in hiding while he regained his strength or hroa. It seems that Sauron may have watched what happened to Melkor and learned a lesson, so he attempted to put some of his power into the Ring in order to maintain it.

Originally Posted by lmp

It should be pointed out that the Ring is, unless heated, unobtrusive, though made of gold. So it appears unextraordinary.

I wouldn't call any gold ring 'unobtrusive' as if you saw one lying on the ground or indeed fished one out of a river, then you would take it. Had he made a brass curtain ring then I think it would have gone unnoticed! However the question remains as to whether he did want it to go unnoticed? Of course, Gold was the metal into which Melkor had infused his power.

The other point arising from the Osanwe-kenta is to do with why Sauron made the Ring, and more to the point, why he helped make the other Rings. From the Sil there is evidence that the three Elven Rings (made in secret) made their bearers able to 'perceive' the One Ring, and we must presume this worked the other way too:

As soon as Sauron set the One Ring upon his finger they were aware of him; and they knew him, and perceived that he would be the master of them, and of all that they wrought. Then in anger and fear they took off their rings.

So this reveals something of the relationship between the Rings, and Osanwe-kenta makes it fall into place as being linked to sanwe. And the bearers of the Three must presumably have had to exercise considerable unwill in preventing Sauron (while he bore the One Ring, at least) from intruding on their thoughts.

Note now that Melkor, due to the right of the incarnate to utilise unwill, i.e. to close their minds to interrogation by others through use of sanwe, was unable to enter every mind. Some he did enter as they did not choose to use their unwill, but others remained shut. In Osanwe-kenta we are told that instead, he used language to enter these minds. Language, the skill which in many (most?) cases made the use of sanwe redundant.

in Valinor Melkor used the Quenya with such mastery that all the Eldar were amazed, for his use could not bettered, scarce equalled even, by the poets and the loremasters.

And what is that special feature of the One Ring? The words, the Black Speech, written in Tengwar, which are only revealed by Fire. A spell of sanwe, written in words, mastered with fire? The Ring Of Words indeed!