It also removes scratches that may be in the glass of your contact printing frame. When I first started contact printing my 4x5 negaitves, I was using the ceiling light in my small 1/2 bathroom as my light source and used the diffusion screens I described above to control the amount of light. But then I switched to a 7 watt light source about 3 feet above the toilet seat top and eliminated the diffusion screens ... and started getting scratches in all my prints... surprisingly all in the same place, yet I couldn't find any scratches on the negatives. Thats when it dawned on me that the diffusion screen layers on top of the frame were eliminating the scratches in the glass.
Originally Posted by JBrunner