Examining wall paintings

Wall paintings in the convent of Muestair (Switzerland) are about to
come loose from the support and must be preserved in situ: (1) the
painted Romanesque plaster (12th Century) which is superimposed on
the painted Carolingian plaster (9th century) in the convent church,
(2) the Pre-romanesque painting (10th century) covered by a
multi-layered thick limewash in the Holy-cross chapel.

Our task is to reveal the present state and its evolution as
accurately and non-invasively as possible in order to understand
which processes are going on, why and how fast they develop. This
requires accurate and reproducible techniques which should
complement and replace the traditional technique by gently knocking
the wall and listening at the sound, as it is practiced by
experienced restorers until now. Most interesting results come from
laser techniques with acoustical excitation of the wall surface.

My questions are:

    1.  How risky is this method for delicate surfaces? By which
        means and criteria can the "safe" excitation be defined?

    2.  How could a supposed long term displacement of specific
        areas be registered, simultaneously and analogously e.g. to
        the climatic evolution? This would require a sort of sensors
        which are capable to measure displacements with an accuracy
        of 0.1 - 1 mm perpendicular to the surface, and this
        continuously.

    3.  Are there further suggestions to approach and solve the
    problem?

Dr. Konrad Zehnder
Institut fuer Denkmalpflege ETHZ
Forschungsstelle Technologie und Konservierung
Hardturmstrasse 181, CH-8005 Zuerich
+41 1 272 1874
Fax: +41 1 272 1965

                                  ***
                  Conservation DistList Instance 12:86
                   Distributed: Monday, May 10, 1999
                       Message Id: cdl-12-86-022
                                  ***