Light contamination of the stored screens can also affect screen sensitivity. To check your screen storage lighting just place a coated screen on the floor before you go home, put a few coins on the screen and leave the lights on overnight. Wash it out in the morning. If the coin's circles fall out first then you have some light contamination that will add up over time and pre flash your screens making details hard to wash out. Also wash out of exposed screens should be in a light safe area. To test this take a 5 gallon bucket of water into the light safe exposing area and develop the image with wet sponges. Sometimes this helps fine details that can get flashed during wash out. (I have had many companies complain that the emulsion is bad when the development is done outside! Even in shade, reflected light and blue sky have enough UV to expose emulsion.)
The other issue with diazo is heat. Above 80 degrees, diazo starts to cook and dark harden. So stored screens are really affected by high summer temps. Anything in the 90-100 degree range is going to cook the coated screen in about a week. You will notice saw toothing and excessive pressure needed to wash out. SBQ and pure photopolymers are unaffected by heat, and can be stored in temps up to 104. As long as you are coating and shooting diazo screens within a couple of days in high heat conditions you are fine.
The one other key area I am seeing is overcoating. Just because one emulsion can be coated 3:2, 2:2 doesn't apply to all emulsions. High solids content, high viscosity emulsions like SP1400, T9, HVP need only 1:1 dull or 1:2 sharp, or 1:1 sharp on really fine meshes. Too much EOM affects details. Great for spot opacity, but typically I look for 6-7% EOM for halftones, 10-15% EOM for spot color.
Al
