PP Crop marks curling

Although I have never seen something like this happen to my plates, I owuld go back to the basics, are the negatives OK, do you have sufficient vacuum? The exposure is bound to be the problem, are all the lights working? Try a piece of plate material at 5 minutes exposure just to totally rule out exposure.

Is the material old? The plate material requires greater exposure as it ages.

Sounds like a drying problem. Are your letting them air dry? Are they drying in a machine or in front of a fan?

What do you use to get the water off once you wash out the plate?

Another possibility to check is that the shoulder of the image is sloped properly rather than straight or even undercut. If you are exposing with a diffuse light source you could be getting undercut, and while it would not be critical for larger areas it would cause a thin line like that to have too little support. Are you using a point light source like an arc light in a platemaker?

Bob

Bob:

It is the diffuse light source which is required to for a good shoulders in platemaking. That is why the commercial production units use flourescent tubes very close to the film/plate sandwich. The diffuse light spreads out and forms the properly angled shoulders during exposure. A point source light will produce a line without sufficient support.

It does appear to me that too little exposure is most likely the culprit in this case.

JHenry

Although I have only worked with steel-backed plates, I thought some plastic backed plates used a back exposure to strengthen the base of the image.
With steel-backed plates I sometimes mask and give very fine lines a supplementary exposure.

Two things. Make sure your water is clean, and that the plates do not sit in the water longer than they should.

My .25 crops will peel, or fall off if they are in water too long.
As long as the water is clean, and I take them out at the correct time, they are fine.