@CaptainKid:
We don't know if it's advanced, because if it was so great why did non of the WB commanders use it?
Probably because Oda didn't want to confuse readers at the time by convoluting the war trying to detail the mechanics of Haki? Remember, Rayleigh said that Busoshoku Haki is an invisible armor worn on the body. If Hardening is just a visual cue for basic Haki then I have a few questions for you:
1. When Tashigi charged Law why wasn't her sword black?
2. When Smoker was clashing with Law why wasn't the Jitte black? If he wasn't using Haki Law would have cut through it like butter.
3. Why weren't Luffy's hands black while holding onto Caesar and Tashigi(in Smokers body) bodies?
4. Why wasn't Tashigi's sword black when she cut Monet?
5. Why wasn't Law's sword black when he cut through Vergo?
6. Why wasn't Doflamingo's hand black when he had Smoker pinned to the ground?
7. Why wasn't Boo's axe black?
Because Hardening is an advanced application of the skill. Unless you believe Oda would make that many, fairly significant, artistic hiccups in the span of 50 or so chapters.