Put a transparent, waterproof, layer between the wet negative and the dry rc paper. Thin polyacetate film should do. If you need a vey lage sheet, use greased tracing paper. Chris http://www.chris-image.co.uk http://www.chrisscrazyideas.co.uk http://www.chrisssoftwareshop.co.uk -----Original Message----- From: owner-photoforum@listserver.isc.rit.edu [mailto:owner-photoforum@listserver.isc.rit.edu]On Behalf Of Guy Glorieux Sent: 04 June 2002 17:23 To: List for Photo/Imaging Educators - Professionals - Students Subject: Printing the Giant Pinhole Negative: A Technical Question Hi all, Printing the giant pinhole paper negative is proving to be a much greater challenge than we ever anticipated and new issues keep surfacing along the way. The basic problem we have to solve negative is the following: how do we make a contact print of a 12.5 x 8.5 feet paper negative with substantial over- exposure in the center and substantial vignetting at the edges. This has raised much more complicated questions than just preparing the basic room set-up for the exposure and calculating pinhole size, f/stop and exposure time to create the negative. This weekend, we thought we had solved every problem along the way and we went ahead with doing the final print. But we've encountered one more problem in the form of a weird chemical reaction when printing the wet paper negative onto wet unexposed RC paper after squeegeeing the two together, emulsion to emulsion. The paper had lost about 1 full stop in sensitivity (compared with the tests we had done just before using the dry paper negative over dry unexposed paper strips) and the positive had unseemly strains and stains all over. The water of the tank in which we had dipped the unexposed paper and the negative had also turned yellowish (I don't think that faulty washing of the paper negative is a factor). After much head scratching and testing, it seems that the solution might be to pre-wash the unexposed paper for about 30 minutes but I'd like to know more about what it is in the unexposed paper that might be responsible for this weird reaction. The paper we are using is Ilford Multigrade IV RC DeLuxe (Pearl). Ilford says that the paper does not have developer in the emulsion. This kind of chemical reaction is something I haven't heard of before and I haven't encountered this before in my own printing from paper negatives. But when doing tests yesterday with standard size paper, I found that this can happen if the unexposed paper is left wet for several minutes before exposure and processing, as if some kind of chemical reaction was taking place on the emulsion before it even reached the developper. Any thoughts or suggestions are most welcome. Cheers, Guy
