Ah yes!

The horns! So, let me explain:
If he is well and truly steamed, it means he’s less likely to be focusing on how his physical shape is manifesting, and more likely that he’s revert back to his raw Maia shape– this is mostly a conceit I use for the purposes of distinguishing what he looks like in a “fair” or human/elven form and the way he looks as a spirit; there’s no particular reason for him to stay in humanoid shape except that A) I like to draw him that way, and B) it’s probably habit for him to look human at this point, since it’s been trillions of years since he was a being of pure energy and spirit.
In my ‘verse, his unmodified Maia shape looks something like this:


The “horns” or head ornaments are sort of how I distinguish Aulë’s Maiar from the Maiar of other Valar. Again, mostly an artistic conceit of mine. XD
This will be easier to showcase once I… uh…. actually draw some more Maiar >__>;; WHICH WILL BE SOON, ACTUALLY.
Here’s Curumo being his usual ingratiating self:

And another, nameless, female Maia:

Later, in the Third Age after he loses his “fair” body in the fall of Numenor, his spirit manifests itself in a very loose, smoky, spectral way that resembles this original form, but more corrupted:


(And missing a finger, naturally).

WOW OKAY THAT WAS PROBABLY A WAY MORE LONGWINDED REPLY THAN YOU WANTED, HUH? :’D ANYWAY, THOSE ARE THE HORNS!
