If there were any famous dark blades in history, I have been unable to find any. Barring the possibility that some historical or ceremonial blade may have been unfinished or made of a particularly dark variety of Damascus steel, searching for historic black blades has been a fruitless exercise for me. The best fictional reference I have been able to come up was to a black blade (also sometimes called the Shade Blade inspired by a black sword called StormBringer, from a fictional series by Michael Moorcock. Interestingly, this StormBringer, and variants thereof, has made it’s way in to numerous computer games, and was, in at least one of them (according to this Wikipedia entry), made “the most powerful magical weapon in the game.” Not surprising, since it would most likely be the rarest weapon in the whole of videogamedom as well… : P
But in all fairness however, I can see why medieval sword makers and swordsmen might not want a black sword. From all accounts, the polishing process made the average medieval sword a better weapon. It was easier to clean, much more aesthetically pleasing, and probably a little lighter too, since the polishing removed a layer of material from the surface of the blade.
In any case, one of my hopes for this blog is that I may eventually gain sufficient exposure to some true professional blade historians who may actually have some insight into the existence of historical black or dark blades. I consider myself fortunate to be live in an age where the technology exists to make functional and durable black swords, even if it requires special steels or artificial finishes… : )