MONITORING

Jacques NEGUER, Inga ZEITLIN, Nicky DAVIDOV
Israel Antiquities Authority, Jerusalem, Israel

Conservation of the fresco paintings, which decorate the podium wall of the Hippodrome of Caesarea and which, was later transformed into an Amphitheatre. The Amphitheatre - created around the middle of the 2nd century AD by cutting off part of the late 1st century BC Herodian structure - occupies the southern third (about 90 - 115 m length) of the original Hippodrome.

The paintings, discovered in 1993, during the archaeological excavations works directed by Dr. Yosef Porath( Director of the excavations of the Caesarea project, Israel Antiquities Authority), represent a unique example of this type of decorated surfaces, featuring several superimposed decorative schemes. These include animals depicted against a foliate background - the earliest and most extensive of the surviving Amphitheatre schemes - as well as more conventional paneled ornaments and other decorative schemes.

At present, more than 80m(the high vary from 0.8 to1.05m) of paintings have been uncovered and stabilized on the eastern and southern walls; a large section of the southern podium wall has been left unexcavated, and the Western Wall almost is entirely destroyed. Up to five (or perhaps more) successive, but discontinuous layers of painting still remain in relatively good state; considering the short period time during which the Amphitheatre was in use (from the mid-2nd century until some time in the 3rd century), this seems to indicate a rather frequent repair and maintenance of the decorated surfaces of the podium walls.

Since its origin, in fact, the environmental conditions of the monument must have been adverse to its conservation, as the seashore is only a few meters away from the Western Wall.

The most environmental decay factors are water (from rainfall, condensation and capillary transport), thermal stresses, wind erosion, water-soluble salts from marine spray and bio-deterioration.

The Graphic Documentation - Specific Problems

At the beginning of the project, the existence of the fresco on the whole surface was not as obvious as it now. The visible surface indicated only the presence of some traces of color and fragments of paint between many layers of plaster. Because this first on the base-map was traced the outline of the plaster and with the progress of the cleaning the fresco design was added with different color. The condition report was completed in 1998. The intervention report will be completed in September 2000 with the end of the project.

We used the archaeological topography grid of Caesarea to situate the base-maps, but we added (marked directly on the wall) more precise measurements for every meter of the fresco.

The condition report was performed using a standardized legend for identifying the problems with a color code for tracing the areas with specific problems on to the base-map. An English Glossary was created by one of the conservators and used for the condition report.

During the two-year process of discovery (involving excavations by the conservators, cleaning and consolidation) we realized how complicated this project is and how fast and unpredictable the deterioration process evolves.

The monitoring process

In order to achieve maximum understanding and control of the deterioration process (and factors), we began to use daily monitoring reports based on the graphic documentation, photography and personal diary. All evidence of damage was recorded on the condition report maps.

Later, when we began to use the automatic monitoring systems, the graphic documentation was connected to the photography monitoring and the remainder of the data collected. We used the same method during the conservation of another fresco - The Saints (the process of documentation was not digital). As it wasn't possible to control the microclimate in the building, it was decided to lift the fresco and transfer it on new supports for museum exhibition.

Design of the monitoring system

The Monitoring system of the Hippodrome fresco was built with the grateful help experts from ICCROM, Istituto Centrale del Restauro, Rome; Courtauld Institute of Art, London; and The National Research Council of Canada.

Visual monitoring - on daily basis: the Hippodrome wall was divided in three areas with conservator responsible for the monitoring. Every day a diary is fulfilled with notes for the observed problems. The observation is marked manually on the corresponding base- map and after this digitized.

Photo-monitoring - on monthly basis: from fixed points rectify photography with color scale is done.

Microbiological growth monitoring - on monthly basis: visits and observation by microbiologist (identification tests if necessary).

Monitoring station - automatic registration of Conductivity (salt content), External and Internal (inside the wall) Temperature and Relative Humidity.

Aerosols monitoring - weekly basis: salt testing of exposed glass samples [10 to 10cm].

Salt testing of the rainwater - will be done this winter for tree months with two Aerosol traps.

Laser scanning - for future precise monitoring of the surface one section of the wall painting was scanned by the team of the National Research Council - Canada.