Color change in prints

Tatiana Falcon <tatia12 [at] hotmail__com> writes

>A museography company has called our lab to see if we can explain
>why some posters designed for an interior exhibit are changing in
>color after three weeks of exposure.
>
>They tell me that the technique used for these prints is the same
>they have been using in diverse exhibitions over the last 4 years,
>and this is the first time that a change of hue appears after a few
>weeks.
>...
>The painting is applied on the reverse side of the substrate and
>then is glued with Scotch high strength adhesive to a glass, so the
>ink is actually trapped between the polycarbonate sheet and the
>glass support.
>
>The prints have changed in color and from the print tests I've seen
>it seems as if the red dyes are the ones fading more promptly.
>
>The museum (in Acapulco, Mexico) says that their exhibition halls
>are controlled, so there seems to be no drastic changes in
>temperature and humidity, and their light resources have uv filters.
>I am wondering if the salinity of the environment could be affecting
>the inks, yet as I said earlier, the printable area of the posters
>are isolated. On the other hand, the print tests archived in Mexico
>City have not changed in color at all. Has anyone heard of a
>similar reaction, and have you determined why?

One thing I can think of offhand would be that if the prints were
sealed before the ink was allowed to fully dry, there might be an
environment of high humidity between the polycarbonate and the
glass. Some modern synthetic inks used in ink jet printing
(particularly the magenta ones) are known to migrate in high RH
conditions, as shown by Andrew Robb (see his article on this: The
effect of relative humidity on ink jet prints. In Conference
proceedings: Preservation and conservation issues related to digital
printing, 26-27 October 2000. London: Institute of Physics, 2001.)

If this were the case, you might not be witnessing the "fading" of
the red dyes, but rather their migration. On the other hand, many
modern inks are not susceptible to this problem. This being said, it
is still advised by manufacturers to allow ink jet prints to dry
thoroughly before they are put away or used.

One other thought: you mentioned an adhesive used for adhering
polycarbonate to glass. I am assuming that it is used over the whole
area of the image? If so, keep in mind that manufacturers are apt to
change the recipes for their products without notice to the users,
and often without changing the brand name or product number either.
An addition of any substance, for example a humectant or
plasticizer, may have been responsible for attacking the magenta
inks or making it more mobile. When you start looking at modern
materials from this point of view, anything is possible! In my
experience there are often so many variables that it can get very
hard nowadays to get repeatable results.

Martin Juergens
Photograph Conservator
Schmilinskystr. 19
20099 Hamburg, Germany
+49 40 2800 4785


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                  Conservation DistList Instance 15:75
                   Distributed: Tuesday, May 7, 2002
                       Message Id: cdl-15-75-006
                                  ***