Bad film

How do I tell if the film (Neg.s) is bad before I make a photo-poly plate? I made a poly plate today and it would not wash out all the way. Checked the film(as far as I could tell it looked fine) changed wash time, changed the water, checked water temp. and even tried washing it by hand. Made two plates from same film both the same. I had our art dept. make another neg. and it washed out fine. I can only assume it was the neg. It will get expensive if I have to do this often. Any suggestions would be greatly appreciated.

Log in to reply   4 replies so far

does the art department have a densitometer? when you hold the original (bad) neg up to the light can you see through the black? if so, the neg isn’t dense enough and you’ll definitely have issues making a plate.

Film may look fine on the light table, but hold it up to a brighter light source, like the fluorescent tubes overhead, and if you can see anything through the non-image areas, the film is not dense enough for a photopolymer relief plate, even if it will work for the thinner emulsions of offset and silkscreen work.

One simple method as parallel_imp indicates is to hold the negative up to a light source/lamp. If you move your finger behind the negative and can see the shadow of it move through the black background areas, the negative is not dense enough.

Thanks parallel_imp we have off set presses and they have not had problems with negs. I will check all my negs with your method. Thank you !