This maybe a stab in the dark but have you tried (presuming you are using Photoshop)
Filter>sketch>notepaper ?
you do need to mess with the sliders ( foreground black, background white)
you could do two seperate settings over two layers and use a mask to get one overall picture
i used the settings 31, 0, 2
to get this
then ( you do get grey ) darkened
with a bit more time and patience could probably get a better effect than this !
Palms