Board Thread:Theories and Speculation/@comment-25283946-20150203145352/@comment-17623-20150204120302

Theory Amaterasu is Fire Release as stated as far back as Databook 1 or 2. Amaterasu being special is black fire that is not able to be manipulated post cast normally. The caster can't make Amaterasu do stuff after setting something on fire and another Fire Release user cannot use it after the fact. The reason why it is black and unmanipulatable is because it also has Yin Release (or whichever one Uchiha seem to get naturally). I base this on the fact that Yin seem to make @*$* black, as seen with Sasuke's Black Chidori when he was hopped up on Hagoromo Juice.

Blaze Release is Fire Release + Yin Release designed specifically to manipulate Amaterasu. Because apparently Yin and Yang Release don't work like everything else and may or may not mix like the others, the two natures technically don't create something new, which goes back to a very old statement I made regarding this "Kishimoto made a new nature to manipulate an existing nature." and in a way he did; this new nature is a nature but not a nature. It manipulates the unmanipulatable by virtue of mixing the two natures to get a result, but the result itself is not necessarily a new nature.