I have been making photopolymer letterpress plates using my vacuum screen printing exposure until with much success. I have one question though…
Would it be possible to expose two plates at once, wash one out and then wash the other one out, or do you need to immediately wash out after exposure or could you wait 5-10 minutes?
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This should not be a problem. To save a lot of time I will gang similar thickness steel-backed and polyester-backed plates for exposure but then wash them out separately (steel or polyester) because of the configuration of my machine. Main thing I suppose is keeping the exposed plates away from ambient light prior to washout.
Gerald-interestingly enough, a plate I exposed then left 1 hr for lunch was better than one immediately developed/processed-same batch of plates, but also maybe better because first warmed up the lights…….anyways, doing a back lit test on B94F Miraclon a la MacDermid web site-useful place….best w.
Always warm up the lamps first. It is the only way to get consistant exposures.
Perhaps the during the time laps a curring or harding took place with the image similar to a post exposure after developing?
I’ve left plates for two days before washing them out with no problem. Just keep them in the dark a few hours will do no harm. Not sure how long you can leave them ultimately, but I used to do this all time. I would gang like 6-7 small plates at a time. Just don’t let them get splashed while you are washing the others - letting water sit on plates that haven’t been post exposed can cause the polymer to curl off the backing.
I’d think that warming up the lamps is good practice but I am not sure how valid it is. Of far more importance I suspect would be warming up the entire operation before you proceed: including bath, machine, raw stock… especially during the winter months. I note that in routine daily operations the bath temp will consistently drop with the first plate and not quite recover. Well, I suppose it might if one was willing to wait around.
There is a bit of latitude in the processing of photopolymer plates. If there were not, DIY operations would not be fruitful.