Digital BW, The Print

OK so I struggled with the topic heading!  I am interesting in creating an effect similar to that 
used by Nick Brandt in some of his images (see  www.nickbrandt.com ).  A good example is 
his Rhino mother and baby" image.  I am not worried about the external border effect but 
rather the liquid-like effect he has used internally close to the border, as if the film plate has 
been damaged by a chemical spill. (See the top centre edge of the image I mentioned.  Also 
see his "Lion Portrait" image.)  I have used the external edge effects in the past (using 
Photographic Edges 6) but have not been able to figure out the internal edge effect.  (I hope 
this makes sense.)  I was thinking of getting some old plate scans but have no idea where to 
find some.  I was even thinking about buying some water colour paint and painting on the my 
scanner glass but thought that this would not end up being realistic.  Any ideas or help 
appreciated.

Steve