Deterioration of polyurethane sculptural relief panels

At the CCA we have recently acquired 14 relief panels by Jim Dine
that were made between 1976 and 1984 to decorate the walls of a
hotel.  They vary in size from about 18 x 24 inches to about 24 x 45
inches. The panels bear all kinds of motifs (including fruit, corn
on the cob, and building tools such as pliers and hammers) in very
high relief.  The motifs appear to be life-size so perhaps they were
cast from moulds made from the real things.  According to the
previous owners the panels are made of polyurethane.  (I hope to
have the plastic analysed to see if that description is accurate.)
They are painted white but, as cracks are now opening up in them, we
can see the ochre-coloured plastic interior.  On each panel the
moulded plastic components are distributed across the surface of an
approximately 3/8 inch thick layer of the same plastic which is, in
turn, laid down on a 1/2 inch thick wood or plywood panel, also
painted white.  I don't know if there are any other materials hidden
by the paint layer.

We received these panels one year ago.  They arrived in Dec. 2002 by
truck from Chicago, where they'd been stored for about 20 years in a
warehouse without climate control.  They arrived wrapped
individually in plastic and packed in cardboard boxes, and they may
have been wrapped this way for many years.  According to a brief
condition report written last July there were at that time a few
cracks around the edges of some panels--nothing dramatically wrong.
But on December 20 2001 a curator noticed them in the climate
controlled vault(68 deg F, 44 %RH) where they have sat, unwrapped,
on shelves, since their arrival, and saw that 4 of the friezes have
experienced what looks like severe shrinkage of the plastic layer:
wide, v-shaped cracks have opened up at the edges, the 3/8 inch
thick layer of plastic which covers the wood panel is beginning to
curl up and pull away from the wood, and where I assume the wood and
plastic layer once met at the edge there is now a gap of about 1/8
inch, the plastic layer having shrunk to a smaller overall dimension
than the wood panel.

Among the remaining 10 panels, several show the beginnings of small
edge cracks and very slight separation between the wood and plastic
layers, and a few show only hair-line cracks between the wood and
plastic layers.

On Dec. 20, when I learned about this problem, I mapped all the
cracks and gaps on the one side of each panel to which we have
access.  Today I compared the length and width of the cracks and
gaps with my maps and don't see any changes.  I will continue to
follow their progress in coming weeks.

Here are my questions:

    1.  Has anyone reading the distlist seen similar friezes by Jim
        Dine?  If so, have they experienced any similar conservation
        problems?

    2.  What could be going wrong?  Could the change of environment
        be causing the problem?  It seems strange that these were
        stored for 20 years in a warehouse where the climate
        fluctuated throughout the year, and now that they are in a
        stable environment they are starting to deteriorate.  Maybe
        this is not a dimensional response to a new environment:
        could something have triggered the chemical degradation of
        the plastic, or could the plastic simply have passed its
        "life expectancy" in, coincidentally, the same year that we
        acquired them?

    3.  Should I take any emergency measures right now to slow down
        their deterioration?  Should I wrap them in plastic with an
        RH indicator inside and outside the package to see if they
        themselves are damper or dryer than the environment, and to
        try to slow their adjustment to our environment, in case RH
        is a factor?  Or, if degradation of the plastic is the
        cause, could that just make them stew in their own vapours
        and deteriorate faster.  These panels are very heavy, and I
        hesitate to have them wrapped in plastic unnecessarily since
        I don't want them to be damaged during handling.

    4.  Any suggestions for their long-term preservation?

Any ideas would be appreciated.

Karen Potje


                                  ***
                  Conservation DistList Instance 15:48
                  Distributed: Monday, January 7, 2002
                       Message Id: cdl-15-48-010
                                  ***