Enchantingly different - must be the ingredients!
This is so unusual in its characters, plot, incredible saga of Severus becoming a smith, and above all, the writing. I love your Slughorn, he's canonical but also so sweet, pathetic and a bit revolting in his self-indulgence, but also quite astute. And caring. As a Slytherin potions expert and Head of House might very well be. :-)
The language you use is as mythical as the Sword, and as strong and rich. This bit, for example:
His wispy face drifted into an expression of dull testudinal musing. "I've heard of this."
I love that word! Especially how it works in the rhythm of these sentences; compact then rolling into that orotund ending, followed by a single short sentence of four one-syllable words. AH! This is not just a story to be savored, but writing to be read and chewed on, sniffed and fondled. Thank you so much for this repast.