It appears that turning back time is possible, given an artful touch and the right technology. We see the proof above our heads as we gaze at the Sistine Chapel frescoes, which now appear much as they did in 1512 when Michelangelo laid down his trowel and brushes. But because they are clean for the first time in centuries, the ceiling's masterworks are prey to the 20th-century dangers Michelangelo couldn't even contemplate. Fortunately, those conserving the frescoes have.
When the skin of dull brown animal glue was rinsed away, revealing the frescoes' lively colors, Vatican officials realized the process of decline would be repeated unless the atmosphere within the chapel's vault could be controlled.
Oily soot was no longer a problem, but the frescoes now would be exposed to particulates from automotive exhaust and aggressive airborne chemical pollutants found in most urban environments. The greatest potential damage, however, could be caused by condensation of moisture on the frescoes' surface and rapid changes in temperature and humidity as throngs of pilgrims and tourists passed through the chapel. With two million people a year visiting the chapel, it is as if everyone in Vienna or Phoenix were passing through, bringing with them tons of moisture to be controlled.
Temperature and air flow studies in the chapel's vault show a geyser of warm moist air erupting toward the ceiling each time visitors enter the space in the morning. This warm air then spreads across the ceiling, cools and descends along the walls. In the process it deposits dirt and can leave behind its moisture if the ceiling's surface temperature is lower than that of the air. Moisture left behind on the frescoes' surface increases the changes for harmful chemical reactions, the formation of moulds or the deposition of salts as the plaster absorbs and then gives off moisture.
This is the paradox at work within the Sistine Chapel: Michelangelo's frescoes, especially after their cleansing, are creations to be shred with the world, yet the thousands gazing upward are the greatest threat to the Renaissance works. The goal, therefore, of the Carrier climate control system now operating in the chapel is to allow visitors by negating the effects of the moisture, heat and dirt they introduce into the atmosphere.
To surround the frescoes with atmospheric stability, the relative humidity of the air bathing the chapel's upper walls and ceiling will be kept at 55% ((5%) year 'round. Relative humidity is the most important single variable, because large swings would permit the porous ceiling plaster to "inhale" and "exhale" water vapor. This flow of water vapor into and out of the plaster could cause deterioration.
The air temperature also must be stabilized, but will be allowed to drift gradually as the seasons change from 25C ((1(C) in the winter. This will minimize the overall temperature differences across the walls and ceiling, reducing thermal stress and keeping any dirt from being attracted to the frescoes' surface.
The choices of these "setpoints" also will insure that the dewpoint (the temperature at which moisture condenses out of the air) will always be several degrees below the surface temperature of the frescoes to prevent moisture accumulation.
The system supplying the environmental stability craved by the frescoes is a collection of individual elements - water chillers, air handlers, pumps, valves, cooling towers - that are tied together by an electronic, computer-based control network that allows separate pieces of equipment to communicate with each other and respond to temperature and humidity information being gathered by sensors within the chapel. An organic comparison is often made: The sensors are the system's eyes and ears; the individual elements are its vital organs; the control system its brain and nervous system.
Since there are better things to look at within the chapel, the 92 sensors (40 of them for redundancy's sake) that continually monitor air temperature, dewpoint and wall and ceiling surface temperatures are virtually invisible. The 26 kilometers of control wiring connecting the sensors to the system's computer-based controls also are hard to detect.
Two computer terminals, one sitting on a table in the Vatican's power station a five-minute walk away and the other residing with the Vatican's restoration scientists, merely allow humans to "talk" to the system and get information from it. The actual orchestration of the air conditioning system's separate elements, based on information being received from the sensors, is handled by microprocessor-based electronic controls distributed throughout the system.
If sensors in the chapel indicate the humidity is rising during a tourist-filled Roman summer day, the electronic control for the air handling unit determines that moisture must be removed from the air by cooling it, since cooler air carries less moisture.
That control signals its counterpart near a Delchi Carrier water chiller, located two floors below the chapel, to begin producing cold water. Other controls on the circuit open valves and start pumps that send the water through pipes on the outside of the chapel's south wall to the air-handling unit manufactured by Carrier France. Outdoor air pulled into the air handler passes over pipes containing the cold water and is dehumidified. The temperature of the dehumidified air is then readjusted to the proper setting by an independent control circuit.
During the winter months, when there are fewer visitors, moisture must be added to the air being pulled in from outside the chapel. The process is reversed as the electronic controls signal the chiller to stop operation and instead open valves that bring hot water from the Vatican's boilers to heating coils in the air handler. The heated air, which now can hold more moisture, passes through an air washer whose high-pressure water nozzles add the needed humidity.
Besides being heated and cooled or humidified and dehumidified, the outdoor air pulled into the air handler is pre-filtered to remove dust and other "larger" particulates. It then passes through a chemical filter to remove gaseous pollutants the air washer missed; and then through a final filer that removes particles like bacteria, pollen or fly ash that are as small as .1 micron or 1/10,000,000th of a meter. All are particles that will no longer get the chance to darken Michelangelo's work.
The air is then ducted up the chapel's outside wall and distributed to individual diffusers concealed carefully beneath the chapel's six south windows.
The diffusers were designed only after the chapel's interior air flow patterns were painstakingly modelled on computers in Carrier's Corporate Engineering laboratories in Syracuse, N.Y. The diffusers create two separate air flows within the chapel - a very low velocity flow over the surface of the frescoes, and a gentle "shower" of conditioned air over the occupants at floor level, effectively isolating the chapel's upper realms from earthly contamination.
Design and installation of the system were, in many ways, team efforts between Carrier and the Vatican's Office of Technical Services, whose employees know the building's intricacies better than anyone. Computer modeling of the Chapel's thermal behavior would have been impossible without the detailed drawings supplied by Vatican Technical Services. Technical Services' general management was the driving force in gaining approval for thousands of details that had to be resolved before the equipment could be installed without damaging the chapel's structural and cultural integrity. They also analyzed the system's capacity independently to make sure it would meet strict requirements.
The Carrier system required engineering expertise from Italy, France and the United Sates, but installing leading-edge technology in a 15th-century structure also required finesse. With solid masonry walls anywhere from 1.5 to three meters thick, installing sensors, ductwork and wiring without disturbing the aesthetic integrity of the chapel required the wisdom of Solomon and the patience of Job, one of whom was watching from a lunette.
The Sistine Chapel is much more than a gallery from the frescoes of Michelangelo, Botticelli, Ghirlandaio and others - it is a functioning chapel used for Vatican religious services. In today's Rome, it may be hard to imagine the quiet of a 16th-century mass in the chapel, with little else but footfalls and perhaps Palestrina's Stabat Mater resonating off the walls. But turning back time has required eliminating as many 20th-century sounds as possible.
Sound-absorbing material in the double-walled air handler muffles much of the sound of moving air and machinery before it reaches the chapel. Sound-deadening material in the diffusers' moveable vanes absorbs most of what remains. The chillers and air handler also are mounted on vibration dampers. And with air conditioning, the windows that once provided ventilation can remain closed to the city's noise and burden of dirt and fumes.
Even if the restorer's art and modern technology can turn time backwards, they can't stop it. So Michelangelo's frescoes must be watched carefully. Perhaps that is the Carrier system's final benefit: history. The electronic control system constantly gathers information that will allow scientists to closely track the chapel's micro-climate. When combined with memory banks full of physical data about the frescoes gathered before and during the restoration, scientists will be able to anticipate any problems that could once again threaten to dim the brilliance of Michelangelo.