from what i've seen at least,
iron artist is when artists offer (usually) 100 commissions slots :))

Iron Artist is basicly a way for artist to better themselves and gain a buck! Through that the pictures have to be monocrome or just one flat color! This allows you to promote yourself and get better at art itself ^^ And if you charge like 5$ a pop people will eat them up and more and more people will know about you!

Ahh yes and its usually 100 slots as well!

100 slots, $5 each ...

$500 for doing some drawings, can't complain in that :D