Backing board

Patricia Smithen <patricia.smithen [at] tate__org__uk> writes

>Has anyone out there tested, used or seen any transparent, rigid
>material that might be suitable for use as a backing board for a
>painting?  I would like to try a number of materials before I decide
>if any are practical for use at our institution.

Here at the ICN (The Netherlands Institute for Cultural Heritage) we
have been studying and testing backboard protections for canvas
paintings for 3 years now.

Our study aimed to understand the effect of a backboard protection
on the RH in the region enclosed between the canvas and the
backboard material. We have identified the 3 parameters which governs
the microclimate in this system: the permeability of the canvas (and
other eventual sources of leakages like holes or open corners), the
total amount of hygroscopic material enclosed in the system (the
canvas, the wooden stretcher, etc.) and the speed of release of
moisture by the hygroscopic materials (the wood, for example,
although providing a large amount of hygroscopic material releases
moisture slowly therefore it has a limited buffering effect for the
RH).

We have developed a physical- mathematical model which combines
these parameters and predict the RH response of backboard protections
and  tested our model with dummy paintings in a climate room.

Among the different materials tested, we used a transparent rigid
polycarbonate resin material called Lexan and produced by General
Electric Plastics which can be of interest for you. In dutch it is
called Kanaal Plaat and it is currently used by Jorgen Wadum at the
Mauritshuis, Den Haag.

We also tested a backboard construction developed by Sarah
Staniforth at the National Trust made of  Melinex, which is
transparent but not rigid as you wish.

We will present our results in a paper and a talk at the Icom
conference in Lyon in the Preventive Conservation Session and a
paper has been accepted by Studies in Conservation and it will be
published in the last issue of this year or the first of next year.

We hope these results can give a quantitative basis to the choice if
applying or not (and how) backboard protections. Do not hesitate to
contact us for more details,

Giovanna Di Pietro and Frank Ligterink
ICN- Netherlands Institute of Cultural Heritage, Amsterdam
G. Metsustraat 8, 1071 KA Amsterdam
+31 20 3054710 775
Fax: +31 20 3054700

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                  Conservation DistList Instance 13:13
                 Distributed: Tuesday, August 10, 1999
                       Message Id: cdl-13-13-001
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