Greenwood said:
don't think it is correct to say that
Sauron specifically made the seven for the
dwarves or specifically to make them greedy.
Almost certainly not; what would have been the point in doing so? If he wanted to control the Dwarves, instilling more greed in them would have more likely turned them all the more
against Sauron (or '
Annatar', hah what a joke).
But I see no implication that the Seven would have given invisibility. Here is my take on the matter:
The One Ring. Its task was to emphasize the inherent power of the
Maia weilding it. If one of lesser stature than a Maia wore it, as a side effect that person would be rendered invisible. This, as I see it, was because of
the Ring's innate nature of possibly granting the wearer extended sight of the Unseen world, in addition to emphasizing the other powers of the Maia.
The Nine. They were completely sullied and under the influence of the One Ring; their task was to enslave the
Men wearing them, to bend them under the will of the maker of
the One (not wielder, maker). Because these Nine rather obviously had a very similar quality of enhancing existing skills, it too had the possibility (probably side-effect) to render their wearers invisible; only the capacity of the Nine was not as great as that of the One, and so even a non-Ainuric being could learn to control his invisibility while wearing one of the Nine (as the
Nazgûl did, and were then turned over time into wraiths).
The Seven. These too were sullied, and had the same task as the Nine did; but because of the remarkable hardihood of the
Naugrim which
Aulë had instilled in them, Sauron's sorceries did not adversely affect the Dwarves. Their lust and maybe luck in finding treasures was most probably increased (Cf. the Seven Hordes), but the main task of the Ring (enslaving the Dwarves) and its side-effect (invisibility) was not achieved (which was why Sauron was so angry). I believe that if, say, a Man would have come across one of the Seven, it would have rendered him invisible in addition to strengthening his lust and luck for treasure.
This is just my take on the matter, upheld by opinions gathered from the texts.
