Color change in prints

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 materials involved are the following:

    Substrate: Polycarbonate sheets

    Ink: Encad GS plus, the manufacturer gives us the following
    composition

        1.  Magenta dye 500 ml.
                Diethylene glycol (CAS No. 111-46-6)
                Triethanolamine (CAS No. 102-71-6)
                Triethanolamine salt of metallised nickel dye

        2.  Cyan dye 500 ml.
                Diethylene glycol (CAS No. 111-46-6) Blue colorant

        3.  Yellow dye 500 m.
                Diethylene glycol (CAS No. 111-46-6) yellow dye

        4.  Black dye 500 ml.
                Diethylene glycol (CAS No. 111-46-6)
                Triethanolamine (102-71) black dye

    **** Moderator's comments: For general information on these inks
    see
    <URL:http://www.encad.com/Inks/Graphic-Standard-PLUS/index.html>

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?

Tatiana Falcon Alvarez
Laboratorio de Diagnostico de Obras de Arte
Instituto de Investigaciones Esteticas, UNAM
Circuito Mario de la Cueva s/n
Zona Cultural, Ciudad Universitaria
Mexico, 04510, D. F.
+52 5 56 22 73 20
+52 5 56 22 75 40-42 ext. 220 and 292
Fax: +52 5 56 65 47 40


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                  Conservation DistList Instance 15:74
                    Distributed: Friday, May 3, 2002
                       Message Id: cdl-15-74-019
                                  ***