I have found that some pens will work well for this type of technique and some don't. The Oil brushes can work as well if they are set with the bristles as far apart as possible. When I really get something that makes sense I'll post a tutorial for anyone who might be interested in trying this in Painter. It will most likely work well in Photoshop if the basic steps are followed.
Create an image and put it on a separate layer.
Add a second layer of all Black over that one and set the option to MULTIPLY.
The use either a scratch board tool or a pen to take away sections of the black layer.
You can reduce the opacity on the black layer so that you can see the image beneath.
Every once in a while I put the opacity on the black layer back to 100 % to check the effect.
The next experiment will have me creating the image first in scratch board (black layer first) and then painting it in watercolors.