I mean, it's pretty simple.

Blood drops from Nords, Imperials, and Redguards (at the moment, it's very basic and more than one blood may drop), and this blood can be smelted into iron ingots.

Uniques aren't properly support at the moment.  Message me here, on reddit at /u/Shanix, and at shanixmgz@gmail.com if I fucked up.