I believe it might be very difficult to get light to pass through anything opaque. Opal glass both "flashed" and true opal will work between a light source, over the negative and paper. I have used a white opalized plastic material from Home Depot for B&W diffusion. Worked, but not as good as an old fashioned sheet of Kodak's Opal glass. Might try a large PPG (Pittsburg Plate Glass) dealer.


Charlie........................................
I kind of wonder why you need a diffused light for contact printing?