Printing the Giant Pinhole Negative: A Technical Question

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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


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