Painting installed on marble wall

Carol Clausen <carol_clausen<-a t->occshost< . >nlm< . >nih< . >gov> writes:

>We are thinking of hanging a framed painting (oil on canvas) on a
>marble panel. The marble slab is an outside wall . . .  In winter the
>marble is much colder to the touch than is the ordinary wall and is,
>I believe, somewhat hygroscopic, so humidity fluctuations are
>probably much greater in its immediate vicinity. I am concerned
>about the effect on the painting of both the fluctuations and the
>difference between the temperature and humidity on its back and its
>front. Are my concerns justified? Would some sort of barrier between
>the marble and the back of the painting provide enough protection?

Yes, your concerns are justified.  For example, we have seen
significant degradation of the interior mortar on thick (about 18")
exterior masonry walls directly behind objects hung on walls for
long periods of time. We have good reason to believe that the
degradation results from high relative humidity in this small zone,
caused by the reduced air circulation and resulting depressed
temperature.  The same mechanism will subject your relatively
fragile easel painting to adverse climate and to severe climate
differences between its face and back.  We believe that the best
prevention is to ensure good convective circulation behind the
painting by keeping the painting well clear of the wall with small
stand-offs.   We have not studied the details of flow, and almost
certainly the standoff distance should increase somewhat with object
size; for a painting say 48" square we believe, 1" clear should be
adequate.  To avoid radiative cooling of the painting's reverse if
the wall is extremely cold, you could apply a reflective shield or
insulator on the wall behind the painting.  Steps would have to be
taken to ensure that condensation either does not occur behind such
a shield, or that such condensation does not cause problems.

G.W. Adams
Cunningham-Adams

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                  Conservation DistList Instance 11:49
                Distributed: Wednesday, December 3, 1997
                       Message Id: cdl-11-49-001
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