- The new micro-climatic control unit (CTA) for visitor access. Reasons and realisation
Gianfranco Martinoni

THE NEW MICRO-CLIMATIC CONTROL UNIT FOR VISITOR ACCESS. 
REASONS AND REALISATION 
In the late 1970s, the first rigorous survey conducted by experts from the Central Institute for Restoration focused on all the problems relating to safeguarding Giotto’s frescoes, following on from the alarm signals that the then-superintendent, Valcanover, had launched in 1970 to the whole world, pointing out that one of the main causes of the deterioration of Giotto’s masterworks in the Arena Chapel was the high level of atmospheric pollution in Padua city centre. 
The project for the conservation of Giotto’s frescoes in Padua stands out as a clear example of how priority has to be given to improving the environment before tackling any type of thorough restoration on the works in question. 
The project, which the mayor of Padua, Zanonato, referred to in the introduction, can be taken as reference model for saving a monument with such complex features as the Scrovegni Chapel. 
As of today, the various study and research activities have been aimed at making the Chapel environment suitable for the conservation of the wall paintings. Many of these actions have already been carried out and the whole project will be completed during the year.
 
Operations already carried out include:
 
1) special double-glazing of the windows with Saint-Gobain glass, combined with a filtering film to reduce ultraviolet and infrared radiation, and improving their closure and insulation by means of new window frames on the outside; 

2) Insulation of the whole roof combined with a new water-proof covering layer, as well as opening up the ventilation holes in the vaulting; 

3) Replacement of 500-watt incandescent light bulbs with cooler 150-watt bulbs (of the halogen type) to prevent harmful micro-turbulence near the frescoed walls; 

4) Start of restoration on the Chapel walls beginning on the inner wall of the facade with the scene of the Last Judgement – the one most seriously damaged both physically and chemically by the process of sulphation affecting the mortar pointing, as well as by the deterioration of the brickwork; 

5) restricting the number of visitors to fifty every twenty minutes. 

One of the most important operations still has to be carried out –  in other words, closure and insulation of the main door in the facade.  It has been shown that large quantities of dust and pollutants come in via this door, and that, especially in the summer, it acts as source of heat (since it faces south-west) badly affecting the frescoes on the nearest walls, especially the Last Judgement where a thermal imbalance is set up with a temperature gradient of about two degrees per linear metre. This situation of marked thermal instability, combined with variations due to the presence of visitors, seemed to be one of the main causes behind the alteration of the paint film, since it creates daily cycles of absorption and evaporation on the walls, up to two-thirds of their height. 
Amongst the solutions put forward, the closure of this door is the most opportune, and is in line with a policy of passive action. This clearly means re-opening the door in the side wall which previously led to the Scrovegni Palazzo, thereby reinstating an element of the original architectural design, and making possible the link with the microclimatic control and filter unit (CTA). This unit, with dimensions of approximately 8 x 8 x 3 metres, will allow a limited number of visitors into the Chapel at a time (not more than 25 every 20 minutes). By means of a double door system, it will ensure that the exterior and the Chapel’s interior are isolated from one another, thereby limiting the quantity of pollutants and the setting up of thermal imbalance within the Chapel.  At the same time, its ventilation and air-conditioning equipment will ensure that visitors entering the Chapel are in a stable state of temperature and humidity (a similar system has already been adopted for people visiting Leonardo da Vinci’s Last Supper in Milan). The unit has been placed along the north-east wall of the Chapel, beside the Sacristy, creating a new route into the Chapel from the nearby Civic Museum, through the Arena public park and gardens. 
Once the unit is in action, the microclimate as well as the physical and chemical conditions inside the Chapel will be continuously monitored to keep a check on the benefits that the new system has produced.
Comparison of previous values with the present ones will provide a complete picture of the improved environmental conditions, thus ensuring protection for Giotto’s frescoes from now on, and enabling maintenance and restoration work to be carried out under almost ideal conditions.

GIAN FRANCO MARTINONI, Padua City Council