Turn my black cast iron doormat to the Rustic brown look

[9ad]

I have a decorative cast iron door mat which has been blackened. I want to remove the black and let the the door mat turn to the weathered rustic brown look.
Does anyone know if this is possible?

Pic here of what i mean:
http://www.strweb.co.uk/howard/doormat.jpg

 

[foxhole]

Its just rusty, wire brush and let the weather do the rest.

 

[TheVictorian]

But then you'll be wiping your feet on a rusty mat and walking brown rust into the house....