[Keeper of Dol Guldur]

About the elven hroa, or that of an experienced Maia, I do not know if Tom Bombadil can be considered Maia, but he is certainly not an elf. So great was his mastery over himself and his own spirit, that when he put the one ring onto his finger, it turned invisible! And when Frodo put the ring on afterward, Tom could still see him! Another interesting note is that the three elven rings were unseen by all eyes, until either the bearer chose to show it or a suspicious person with a scrutinous eye searched. Nobody had any idea that Galadriel had a ring, until she showed it to Frodo, and the same would go for Gandalf and Lord Elrond. It was stated somewhere that the other sixteen rings, those given to men and dwarves, did indeed have the power to turn the wearers invisible. Whether or not the weaker rings (weaker than the one) could be controlled, and the bearers could chose to become invisible, is unknown. But Tom Bombadil certainly supports this theory of how the invisibility of the one ring works.