http://youtu.be/M9kD9hjv9FQ?list=PLBtVQjMo9-s4dNzVqrx-aWp8c5EFtKRuo
This is a useful tutorial series from Will Salley about how to make digital negatives.
It is for albumen prints, but the process is the same for polymer photogravures, cyanotypes, etc.
The entire series is worth watching.
And here is a link to my post about how to make your own step wedge.
http://artandwater.blogspot.com/2014/03/make-your-own-11-step-wedge-for-digital.html
