[Healeys] Non Healey rusty question

[Mike Brouillette]

Guys,

        I have a Non Healey rusty question?  I am looking to take an old 
pickup truck tailgate and use it as a wallhanger piece.  It has some rust, 
and great aged paint.  What I would like to do is convert the rust but leave 
the paint as it is, so when you look at the piece closely, it shows the edge 
going from converted rust to paint without the look of repainted or 
primered, just the blackish converted rust.

  Anyone have any suggestions on what product might give me that effect?

Thanks in advance,
Mike Brouillette
59 BT7