Try patches of pva glue and then drip super-glue onto it. Then wash with a black ink.
The results look something like this:
http://www.dakkadakka.com/dakkaforum/posts/list/548188.page
I saw a thread on here about a guy showing the same technique (thats where i got the idea from), his thread should be on here if you do a bit of digging
Hope this helps buddy.