Hard to Fathom..

[Gorthol]

"The chief power (of all the rings alike) was the prevention or slowing of decay (i.e. `change' viewed as a regrettable thing), the preservation of what is desired or loved, or its semblance -this is more or less an Elvish motive. But also they enhanced the natural powers of a possessor - thus approaching `magic', a motive easily corruptible into evil, a lust for domination. And finally they had other powers, more directly derived from Sauron...such as rendering invisible the material body, and making things of the invisible world visible." [5]

It's to be found in several places that they did confere invisibility.

So where are we now with our Dwarfking wearing one of the Seven:

* He's greedy as hell.
* He's quick to lose temper.
* He's got a lust for domination of others.

* He's got unending life, will not fade to the shadow world cause he's too solid.
* He can't be dominated by others, nor can anyone read his heart through the ring he wears.
* He's got a ring with a capability of enhancing his natural powers. Which makes him even more kingly.
* His ring will slow the passage of time and preserve beauty.
* He can *at will* become invisble, see the invisible world and all there in, and return whenever he wants to.

Well, I give you a greedy dwarf who wants to dominate others, and lives forever, and can be invisble even when fighting, that's a helluva killer machine.