Not really reread it,
First Mihawk was asking Zoro if He broke his Sword, then Mihawk said If u infused Haki with it, it wouldn't be broken which means CoA. Then saying Every Weapon can turned into Black Blade like Mine without mentioning Haki or CoA, which had a vague meanings. Either it can be mean turned temporarily or Permanently.
To me Basic CoA or even Master CoA only capable to maintain the Black Blade esque temporarily. We've seen it on multiple Top Tiers.
Plus if its only CoA Haki, then Shouldn't Top Tiers like Roger WB etc had their weapon become Black Blade?