Faded photograph prints

I am a Restorer of Fine Art in Johanesburg, South Africa. One of my
clients is a wildlife painter and photographer and has recently
encountered the following problem:

   "I have been printing photographic prints using an HP designjet
    5500 printer with standard dye inks. I print onto Hahne Muhle
    photorag paper. The prints are essentially tinted black and
    white (sepia type)--printed in 4 colour CMYK. I started running
    prints about 4 months ago. One of the first prints that I ran
    has turned green. It is the only one out of the initial 30 that
    this has happened to so I thought that it must have been left in
    the sun or mistreated somehow. I have now however had reports of
    3 others that this is happening to. It appears to be individual
    prints out of runs, not complete runs. Any ideas as to why this
    may be happening?"


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                  Conservation DistList Instance 20:31
                Distributed: Saturday, December 9, 2006
                       Message Id: cdl-20-31-021
                                  ***